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winter months, growth is reduced as evidenced by presence of only ver;' 3.nail
shoots.
Temperature, Salinity, Sediments
Continuous temperature recordings taken at the Virginia Institute of
Marine Science provided more detailed information on temperature patterns
during the course of this study (Fig. 16). Although temperature in the
shallows may fluctuate during the day, temperatures taken at the sampling
sites during routine sampling, as well as from other sub-projects (e.g. the
seed germination experiments), revealed very similar trends as that provided
by the permanent recording equipment.
Minimal water temperatures occurred in January or February in all three
years with lowest recorded temperatures approaching 1°C. Temperatures in the
shallows where the grasses occurred probably were close to 0°C or less
because of the fact that these areas had ice coverage during the winter
period.
Maximal summer temperatures were reached in July or August with
temperatures reaching 29°C in each year. Temperatures between the summer
maxima and the winter minimum were also similar for 1978, 1979 and 1980.
Continuous salinity measurements were not available from VIMS. However,
salinity samples taken routinely during the study period indicated salinities
at all three sites for the biomass sampling to be quite similar. Salinities
were always lowest in the spring and highest in the late summer or fall.
Salinity range in 1979 was 12.4 to 19.0 °/oo, while in 1980 it was 15.8 to
24.5 °/oo. The latter half of 1980 was extremely dry, with little runoff
from land, accounting for the higher salinities recorded that year.
Sediments at the five sites consisted primarily of sand with lesser
percentages of silt and clay (Table 10). The Guinea Marsh inshore site,
which is more protected as well as being fronted by the large, expansive
grass flats has more silt and clay than the other sites. The quiet water
conditions here would allow finer sediments to accumulate. Median grain size
ranged from 2.4 0 at the Browns Bay site to 3.1 0 at the Guinea Marsh inshore
area
DISCUSSION
Despite some differences that existed among the sampling sites for the
measured parameters, several trends were evident from the data. One very
interesting aspect was that there were large differences between years for
both maximum and minimum values (Tables 11 and 12) of parameters such as
shoot standing crop, shoot density and number of reproductive shoots. The
standing crop of vegetative shoots was always highest in the June-July period
at all sites while minimal values for standing crop occurred during the fall
or winter months in both years. However, the standing crop of Zostera. marina
during the June-July period in 1980 was higher compared to 1979 at all sites.
The fact that all sites showed this trend suggests that possibly the grass
47
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Browns Bay
Sand Silt & Clay Median (Mdfl)
June, 1980 88.5 11.5 2.4
Nov., 1980 85.0 15.0 2.5
Guinea Marsh
Offshore 86.4 13.6 2.6
Inshore 77.3 22.7 3.1
Vaucluse Shores
Zostera 91.5 8.5 2.8
Mixed 92.2 7.8 2.9
TABLE 10. PERCENT SAND AND SILT AND CLAY IN SEDIMENTS COLLECTED FROM THE
STUDY SITES AND MEDIAN GRAIN SIZE (PHI UNITS, 0, where 0 = - Iog2 ram). j
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TABLE 11. MAXIMUM AND MINIMUM VALUES FOR SHOOT AND ROOT-RHIZOME STAK51NT CROP FOR
ALL SITES (MONTHS IN PARENTHESIS ARE FOR WHEN THE VALUE WAS RECORDED)
SOME SITES WERE NOT SAMPLED FOR THE ENTIRE YEAR (DATA FROM TABLES 2,3,
'», 5 and 7).
Browns Bay
1978
1979
1980
Guinea Marsh
Offshore
1978
1979
1980
Guinea Marsh
Inshore
I9-»9
1980
Vaucluse Shores
Zostera
1978
1979
1980
Vaucluse Shores
Mixed
1979
1980
Shoot Standing
Max.
161 (July)
173(June)
158(Aug.)
336 (June)
397 (July)
291 (June)
4 12 (July)
161 (July)
230(July)
138(July)
161 (July)
Crop (g/m ) Root-Rhizome Standing Crop (g/n )
Min. Max. Min.
23 (Oct.)
9 (Sept) 11 (March)
A8 (March)
57 (Oct.)
70(Nov.) 3/.(March)
33 (March)
9(0ct.)
2 (Jan.)
28(Sept.)
12 (March)
54 (March)
37 (May)
52(Jan.)
155(July)
206 (June)
105 (June)
130(June,July)
155(June)
61 (June)
121 (July)
130(Dec.)
121(Aprll)
112(July)
130(Feb.)
6(0ct.)
15(Sept)
48 (March)
10(0ct.)
42 (Nov.)
88(?eb.)
3(Nov.)
KJan.)
12(Dec.)
61 (Sept.)
103(Feb.)
20(May)
52(Jan.)
8 (March)
lO(March)
6 (March)
50
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beds may be responding to some external environmental control for biomass
production (e.g. temperature) or even a biological control mechanism [e.g.
waterfowl interactions (Jupp and Spence, 1977)] that affects all grass beds,
and which can vary from year to year.
Root-rhizome standing crop followed similar trends as the shoot standing
crop except for some variation at the Vaucluse Shore sites.
The pattern of growth as expressed in shoot denisty was different than
the shoot standing crop. Lowest density of shoots occurred in the late
sunnier to early fall period, while highest density occurred in the spring and
early summer period. Appearance and growth of new shoots were not observed
to occur after mid-August which coincides with the defoliation period when
older leaves and shoots slough off after water temperatures peaked between 25
and 30 °C. New shoots were first observed after the sunnier dieback around the
end of September and early October as evidenced by the appearance of new,
small (<5cm) shoots. New shoots appeared to be constantly produced
throughout the winter and spring as confirmed by visual examination of the
biomass samples during processing and the plots of the size frequency
histograms. The large production of new shoots in the fall and winter
resulted in this period having very high shoot densities compared with the
early summer period prior to the defoliation of the older leaves. The
reduction in shoot density from the spring to the early summer period may be
a result of a self shading mechanism or temperature stress. Although data
are not available, it is possible that as leaves rapidly elongate in the
spring, sufficient light may not reach the sediment surface where the new
shoots would be found, especially in very dense beds, to allow these new
shoots to grow.
The mean length of the shoots showed a distinct trend for all sites.
Leaf elongation began around March and continued through the June-July period
where the mean length was always longest (Zostera marina at the Vaucluse
Shores mixed site reached peak length in May but this may be a result of
temperatures rising faster in this shallower area compared to the deeper
Zostera site, thus causing "L. marina to grow faster here). Leaf length
decreased from mid-summer to March us a result of loss of longer older leaves
aad shoots in the late summer along with the increased production of new,
smaller shoots in the late fall and winter period. This was evident in the
frequency diagrams of the different size class categories which always showed
a large percentage of small shoots in the March period.
The contribution of seedlings and subsequent seedling growth in Zostera
marina beds can be highly variable because of differential seed recruitment
which is dependent upon not only seed production within a particular area but
possible seed dispersal from other areas. The number of reproductive shoots
in a particular area can be highly variable from year to year. The number of
seedlings observed at the Guinea Marsh inshore area was high. This could be
the result of either limited dispersal of seeds produced in this area (the
site was semi-protr:ted in a small embayment) or a large dispersal of seeds
washed into this area from the adjacent area. This large number of seedlings
was the cause for this area to revegetate as rapidly as it dia (new shoot
production from old rhiaome stock was small at this site compared to the
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other sites (Table 4, Fig. 4). Despite the shorter mean length of shoots in
1980 compared to 1979, the large increase in the number of shoots in 1980
over 1979 resulted in the greater shoot biomass in 1980.
Zostera marina in the Chesapoake Bay exhibits distinct seasonal trends
in its growth cycle as observed from all the data collected from the
different sites. Growth does occur in terms of new shoot production in all
months except from mid-July to mid- to late September. Because of high
summer temperatures in these shallow areas where Z_. marina grows (up to
29°C), growth stops with no new shoot production occurring with the plants.
In the early fall as temperatures decline to between 20-25°C, new shoot
production from the existing vegetative stock begins and continues through
the late spring period. Seed germination (see section on seed germination
aspects) begins in late October and continues through, at least, April and
possibly early May. Growth of seedlings is rapid especially for the period
from March to May. Because of new shoot production, shoot density increases
in the fall and remains high until June and July. The smaller, new shoots
depresses the mean length until March, when, as the temperatures begin to
increase above 5-10°C, rapid growth causes mean length and thus shoot biomass
to increase. The period of sexual reproduction occurs from approximately
mid- to late February until early June, when all seed have been released.
The trends described above for jSpslera marina in the Bay parallel those
described in other studies of Bay Z. marina populations (March, 1970, 1973;
Orth and Heck, 1980). Data for other Z_. marina beds on the East Coast of the
United States are limited but are available for North Carolina and Long
Island Sound. In North Carolina (Dillon, 1971; Penhale, 1977) "L. marina
growth and defoliation is shifted by about one month before those events that
occur in the Bay while in Long Island Sound (Burkholder and Doheny, 1968)
growth occurs approximately one month later than in the Bay. Because of the
latitudinal separation of all three sites, we suggest that temperature is a
very important factor for regulating the growth of Z. marina and that the
shift in growth of Z_. marina proceeding northward appears to be directly
related to water temperatures, rising earlier in North Carolina and later in
Long Island Sound. Although temperature is an important factor, we also
agree with Jacobs and Pierson (1981) that irradiance also varies with
latitude, and that this may have subtle effects on the phenology. Bachman
and Barilotti (1976) concluded that irradiance was important for flowering.
However, before conclusions, on the ultimate factors that affect growth,
further experimentaion is necessary for elucidation of what influence both
temperature and irradiance have on the seasonal growth cycle.
Comparison of seasonal trends in standing stock of Zostera marina in the
Bay and that in Japan indicate close similarity in patterns for shoot density
and standing crop of leaves and roots and rhizomes (Mukai et al., 1979, 198C;
Aioi, 1980; Aioi et al., 1980). This would be expected because of the
similarity in latitude (37° for Chesapake Bay, 35° for study site in Japan)
and similarity in water temperature patterns, although water temperatures in
the Bay are colder in the winter months (0°C for Bay, 10°C for Japan).
However, the Japanese rsearchers felt that insolation was the critical factor
rather than temperature although Aiai et al. (1980) suggested temperature may
be essential for differentiation of generative organs.
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The data presented here adds to the basic knowledge on the biology of
Zostera marina in the Chesapeake Bay. Despite these contributions,
significant questions remained unanswered: What is the relative contribution
of temperature and irradiance to che growth cycle? How do sediment nutrients
change seasonally and what is their affect on seagrass production? What is
the relative contribution of epiphytes, both macro and micro, sediment flora
and seagrass to the total productivity of the system? Is Zostera marina
nutrient limited in the Bay? What are the factors that allow "I* marina and
Ruppia maritima to coexist in tne shallow water but not in deeper water? How
do annual changes in runoff affect light quality and quantity at different
vegecated sites. How do annual changes in iiradiance affect vegetative and
reproductive growth? What controls maximum stancing crop in an area? Does a
vegetated area ever become totally senescent so ss to result in a total die
back in one year as we observed at a Guinea Marsh site? How important is
seed recruitment and germination to the ultimate maintenance of the existing
bed? These represent some of the significant areas where future research
lies.
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REFERENCES |]
11
Aioi, K. 1980. Seasonal changes in the standing crop of eelgrass (Zostera
marina L.) in Odawa Bay, Central Japan. Aquat. Bot. 8:343-354.
Aioi, K., H. Mukai, I. Koike, M. Ohtsu, and A. Hattori. 1980. Growth and
organic production of eelgrass (Zostera marina L.) in temperate waters
of the Pacific Coast of Japan. II. Growth analysis in winter. Aquat.
Bot. ]0:175-182.
Andorson, R. R. and R. T. Macomber. 1980. Distribution of submersed
vascular plants, Chesapeake Bay, Maryland. Final Report, USEPA, i
Chesapeake Bay Program Grant No. R805977. 117 pp. |
Burkholder, P. R. and T. E. Doheny. 1965. The biology of eelgrass. Lament
Geol. Observatory No. 1227. 120 pp.
Dillon, C. R. 1971. A comparative study of the primary productivity of
estuarine phytoplankton and macrobenthic plants. Ph.D. Thesis. Univ.
North Carolina, Chapel Hill. 119 pp.
Folk, R. L. 1961. Petrology of sedimentary rocks. Hemphill's, Austin
Texas. 154 pp.
den Hartog, C. 1970. The seagrasses of the world. Verhandel, Afd. Naturk.
Kominklyke, Ked. Akad. Van Werenscl. Tweede Reeks. Dul. 59, No. 1.
275 pp.
Jacobs, R. P. W. M. 1979. Distribution and aspects of the production and
biomass of eelgrass, Zostera marina L., at Roscoff, France. Aquat. Bot.
7:151-172.
Jacobs, R. P. W. M. and E. S. Pierson. 1981. Phenology of reproductive
shoots of eelgrass, Zostera marina L., at Roscoff (France). Aquat. Bot.
10:45-60.
Jupp, B. P. and D. H. N. Spence. 1977. Limitations of macrophytes in a
eutrophic lake, Loch Leven. II. Wave action, sediments and waterfowl
grazing. J. Ecol. 65:431-446.
Marsh, G. A. 1970. A seasonal study of Zostera epibiota in the York River,
Virginia. Ph.D. Thesis. College of William and Mary, Williamsburg, Va.
155 pp.
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Harsh, G. A. 1973. The Zostera epifaunal community in the York River,
Virginia. Chesapeake Sci. 14:87-97,
Marsh, G. A. 1976. Ecology of the gastropod epifauna of eelgrass in a
Virginia estuary. Chesapeake Sci. 17:182-187.
McRoy, C. P. 1966. Standing stock and ecology of eelgrass in Izembek
Lagoon, Alaska. M.S. Thesis. Univ. Washington, Seattle. 138 pp.
McRoy, C. P. 1969. Eelgrass under Arctic winter ice. Nature 224:818-819.
Mukai, H., K. Aioi, and Y. Ishida. 1980. Distribution and biomass of
eelgrass (Zostera marina L.) and other seagrasses in Odawa Bay, Central
Japan. Aquat. Bot. 8:337-342.
Mukai, H., K. Aioi, I. Toike, H. lizumi, M. Ohtsu and A. Hattori. 1979.
Growth and organic production of eelgrass (Zostera marJna L.) in
temperate waters of the Pacific Coast of Japan. I. Growth analysis in
spring-summer. Aquat. Bot. 7:47-56.
Orth, R. J. 1973. Benthic infauna of eelgrass, Zostera marina beds.
Chesapeake Sci. 14:258-269.
Orth, R. J. 1977. The importance of sediment stability in seagrass
communities. Pp. 281-300 jin_ B. C. Coull (ed.), Ecology of Marine
Benthos. Univ. South Carolina Press, Columbia.
Orth R. J. and K. L. Heck, Jr., 1980. Structural components of eelgrass
(Zostera marina) meadows in the Lower Chesapeake Bay-Fishes. Estuaries
3": 278-288"
Orth, R. J., K. A. Moore and H. Gordon, 1979. Distribution and abundance of
submerged aquatic vegetation in the lower Chesapeake Bay, Virginia.
USEPA Final Report, Chesapeake Bay Program. EPA-600/8-79-029/SAV 1.
Phillips, R. C. 1972. Ecological life history of Zostera marina L.
(eelgrass) in Puget Sound, Washington. Ph.D. Thesis. Univ. Washington,
Seattle. 154 pp.
Phillips, R. C. 1974. Temperate grass flats. Pp. 244-299 ji£ H. T. Odum, B.
J. Copeland and E. A. McMahan (eds.), Coastal ecological systems of the
United States, Vol. 2, Conserv. Found., Washington D.C.
Setchell, W. A. 1929. Morphological and phenological notes on Zostera
marina L. Univ. California Publ. Bot. 14:389-452.
Thayer, G. M., P. A. Wolfe and R. B. Williams. 1975. The impact of man on
seagrass ecosystems. Amer. Scient. 63:288-29C.
Wood, W. J. F., W. E. Odum and J. C. Zieman, 1969. Influence of seagrasses
on the productivity of coastal lagoons. Lagunas Costeras, un Simposio.
Mem. Simp. Intern. Lagunas Costera. UNAM-UNESCO pp. 495-502.
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W. **»«l'-"«*PB', trnt'-at
CHAPTER 2
ANTHESIS AND SEED PRODUCTION IN ZOETERA MARINA L. (EE'.GRASS)
FROM THE CHESAPEAKE BAY*
by
G. M. Silberhorn
R. J. Orth
and
K. A. Moore
I
• • *Accepted for publication in Aquatic Botany.
Contribution No. 1068 from the Virginia Institute of Marine Science, College
of William and Mary.
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ABSTRACT
Anthesis and seed production in Zostera marina were studied in three
areas of the Chesapeake Bay from January to June i960. Spadix primordia with
distinguishable anthers and pistils were first observed in February when
water temperature was 2°C. Development of the reproductive shoots in the
field continued after February as water temperature rose, with the first
evidence of pollen release in mid-April (water temperature 14.3*0). Stigmata
loss was first observed in samples taken in late April at two of the areas as
water temperatures averaged above 16eC. Pollination was complete at all
locations by 19 May and anthers were no longer present. Few reproductive
shoots were found on 3-5 June and seed release was assumed to be complete by
this time (water temperature 25*C). The density of flowering shoots ranged
from 11 to 19Z of the total number of shoots, producing an estimated 8127
seeds us" .
Comparison of flowering events with other areas along a latitudinal
gradient from North Carolina to Canada indicated that reproductive events
occurred earlier in the most southern locations and at successively later
dates with increasing latitude.
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1
INTRODUCTION
Anthesis and seed production are two critical stages in the life cycle
of seagrasses. Despite the ultimate importance of flowering in seagrasses,
few studies have described, in detail, these processes and the factors that
initiate it. Most notable for the species Zostera marina L. are those
studies by Churchill and Riner (1978), DeCock (1980, 1981a, 1981b, 1981c) and
Jacobs and Pierson (1981). DeCock conducted extensive laboratory studies on
"L. mar inf. populations collected frota the Netherlands and compared this with
field plants while Churchill and Riner (1978) have presented a detailed
account of anthesis and seed production in North America "L. marina
populations. Except for the Churchill and Riner (1978) study, these aspects
have been only briefly reported on in a few other papers for North American
Z. marina populations (Setchell, 1929; Taylor, 1957; McRoy, 1970; Dillon,
1971; Phillips, 1972; Keddy and Patriquin, 1978).
The objectives of our work were to describe the timin6 of the events in
the flowering process for lower Chesapeake Bay Zostera marina beds and to
compare this information with data available for other locations along the
east coast of the United States. The nature of flowering of North American
populations and those of European counterparts are also compared.
STUDY SITES, MATERIALS AND METHODS
Zostera marina was collected from three locations in the lower
Chesapeake Bay in 1980 to ascertain rhe timing of the flowering events (Fig.
1). Site 1 was located in the Mobjack Bay near Browns Bay. The dominant
vegetation at this site is Z_, marina although it co-occurs with Ruppia
maritima (widgeon grass). The vegetation in this area is found in a 400 m
wide bed parallel to the shoreline. There are approximately 41 ha of bottom
covered with vegetation in the immediate vicinity of this site (Otth et al.,
1979). The sampling location was at a water depth of 0.5 m MLW (mean low
water).
Site 2 was located at the mouth of the York River adjacent to the Guinea
Marshes in a monospecific stand of Z_. marina. This, area is an expansive
shoal (<1.5 m MLW) which is almost entirely vegetated by 2^. marina. There
are approximately 309 ha of bottom covered by Z. marina in and adjacent to
this site (Orth et al., 1979). Depth of water at the sampling location was
approximately 0.75 m (MLW).
Site 3 was located on the western side of the Eastern Shore of Virginia
in an area called Vaucluse Shores, This area is dominated by _R. maritiiaa in
the very shallow water (0.3 m - MLW), "L. marina in the deepe^ water
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Fig. 1. Location of the three study sites (1,2,3) in the Chesapeake Bay.
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(>1.0 m MLW) and a mixture of the two grasses at intermediate depths. The
vegetation at this site is found between the shoreline and an offshore
sandbar, located 500-700 m from shore. There are 211 ha of bottom covered by
vegetation in this area (Orth et al., 1979). The sampling location was in
the deeper, Z_. marina portion where a water depth was approximately 1 m
(MLW).
Weekly collections of individual shoots were made beginning 18 January
1980 at each of the sites to ascertain the beginning of the flowering period.
Afterwards, replicate samples of 0.033 m^ were taken using a large,
plexiglass corer. The entire core of leaves, roots and rhizomes were placed
in a coarse mesh bag, rinsed free of sediments and placed in a bucket of
water for later analysis. Water temperatures were either taken at the sites
or were obtained from a nearby recording station. Samples were brought to
the laboratory and vegetative and reproductive (generative) shoots! were
separated, counted and recorded. Spadices were dissected from the shoots
their position hierarchy noted (terminal rhipidium, rhipidia branches 3,2,1)
similar to that defined by DeCock (1981). Selected spadices were preserved
in 70% EtOH for further examination. The length of each spadix and number
per rhipidium and shoot were determined. Anthers and pistils were counted
and size range measurements within each spadix were recorded.
RESULTS
No reproductive shoots were observed at the sampling sites until 14
February 1980. Shoots from the Guinea Marshes (site 2) and Eastern Shore
(site 3) contained spadices which ranged from 0.5-3.5 cm long. Anthers were
in a primordial stage of development, but could be clearly distinguished as
they had obtained their characteristic elongated, elliptical shape (Fig. 2a).
The size of the largest ones (4-5 mm) were comparable to anthers collected as
late as May. In contrast, pistils were quite immature with many as yet
undeveloped. They ranged in size from 0.2-0.8 mm and appeared to be round
and bun-like with no differentiation of ovule, style or stigmata. Water
temperature readings were 3.0°C for each of the sites. Data on the mean
numbers of rhipidium, spadices, pistils, pollens sacs and percent of
fertilized embryos for all the sampling dates at the three sites are
presented in Table 1. During February and March the reproductive shoots
generally contained only one rhipidium with one or two spadices per
rhipidium. The ratio of pollen sacs to pistils within the spadices during
February was greater than 2:1, reflecting the undeveloped state of the
pistils, assuming one pistil will develop with each two pollen sacs in the
spadices.
Development of the reproductive shoots in the field continued after
Feburary as water temperature increased, with the first evidence of pollen
release observed in samples taken on 10 April from site 3. The average water
temperature was 14.3'C. By this time, the pistils were fully differentiated
into ovule, style and bifurcated stigmata (Fig, 2b) and some were in erection
stage as described by DeCock (1980). In these samples, maximum anther length
was 6 mm and maximum pistil length was 5 mm. Among the uamples taken during
March and early April the ratio of pollen sacs to pistils was approximately
61
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2:1 reflecting more developed nature of the spadicas. Although the mean
number of spadices per shoot was still less than 2 on the 10 April sampling
date, additional spadices had developed since March. These were generally
smaller in size than the existing spathes resulting in a lower mean number of
pollen sacs and pistils per spadice. Along the rhipida the spadices were
observed to develop acropetally with decreasing size spathes with increasing
branch number as described by Churchill and Riner (1978).
Stig-nata loss was first observed in samples taken on 21 April at sites 1
and 2 when water temperatures averaged 16.2°C. The scar tissue at the point
of abscission appeared to be reddish brown with the abscission zone located
in a slightly swollen area of the style immediately subtending the bifurcated
stigj-.jta. The abscissed pistils ranged from 3.7-5.2 mm long. Of the 101
spadicas observed, pollen sacs were missing in 14, an indication that
pollination had begun. The presence for the firbt time of fertilized embryos
also marked this event. Rapid growth of the reproductive shoots was evident
by this time with increases in the numbers of rhipidia per shoot to an
average of nearly three. New rhipidia developed basepetally and each new
rhipidium consisted of a decreasing number of spadices as compared to the
more terminal rhipidia on the shoot. Of the three sites it appeared that
site 3, along the Eastern Shore of the Bay, may have been delayed one to two
weeks in reaching a developmental stage similar to the western shore sites.
Pollination was complete at all locations by 19 May. Anthers were
almost totally absent as evidenced in Table 1. All that regained in the
spadices were embryos at various stages of d elopmert (striations of the
seed coat would be detected) and degeneratin , unfertilized pistils (Fig. 2c).
A few seeds had dehisced as evidenced by perio.arp vestiges (Fig. 2d). Most
rapid embryo development and corresponding pollen sac dehiscence occurred
between 21 April and 21 May at sites 1 and 2, and between 2-28 May at site 3.
By 28 May, it was apparent that the fruiting process was at full maturity at
all the sites. Water temperatures ranged from 20-21°C during this period.
The characteristic markings on the seed coat were obvious and the pericarp of
many of the fruits were bursting. Nonviable degenerating pistilc were nearly
gone and a small number of seeds had been released. The maximum percent of
fertilized embryos observed prior to seed release was 59 at sites 1 and 2,
and 87 at site 3 (Table 1). Although the mean number of rhipidium per shoot
at maximum development in May exceeded rhree for each of the sites, a range
in sizes was observed throughout the bads. Many shoots still consisted of
only one rhipidium while the maximum observed was four.
An attempt was made to collect material on 3 June at sites 1 and 2 and
on 5 June at site 3. Water temperature was 15°C at this time. However,
there was a widespread deterioration of reproductive shoots. Entire shoots
were floating at the surface, many of them lacking spadices. Those still
rooted had deteriorated as well. The spadices that were present had only a
few seeds and seed release was considered essentially complete. Because of
these conditions no collections or data were taken.
The maximum density of reproductive shoots collected from each of the
sites ranged from 303-424 per m2 or 11-19X of the total number of shoots
(vegetative and reproductive). The mean length of the reproductive shoots
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TILS PER SPADICE
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ranged from 20.7 cm at the Browns Bay site, to 33.6 cm at the Vaucluse Shores
site. Assuming that the mean of 68% of the ovaries which had developed into
fertilized embryos by late May (Table 1) equaled the percent of seeds
produced, populations of Zostera marina from th<; three study sites produced
an average of 23 seeds per shoot. Using a mean density of 353 reproductive
shoots m~2, an average of fc!27 seeds m~^ were produced in the Chesapeake Bay
Z. marina beds.
DISCUSSION
Since Setchell's (1929) classical work on the phenology of Zostera
marina and his emphasis on the importance of temperature as a controlling
mechanism for the different stages in the life cycle of Z^. marina, numerous
workers have compared their phenological data from various localities to
either corroborate or refute the original hypothesis (Tutin, 1938; McRoy,
1970; Phillips, 1972; Felger and McRoy, 1975; Harrison and Mann, 1975;
Churchill and Riner, 1978; DeCock, 1980; Jacobs and Pierson, 1981). In
addition to temperature, irradiance has been implicated as an important
factor especially as it relates to floral induction (Backman and Barilotti,
1976; Churchill and Riner, 1978).
The data from our study document the successive development of the
flowering process. Initial observations of the immature flowerss were
obtained in February when water temperatures were 3°C. Completion of the
flowering process when mature seeds are released was observed in late
May-early June when water temperatures were 23-25°C.
Our data corroborated much of the detailed information on flowering of
Zostera marina in New York by Churchill and Riner (1978) although some slight
differences exist. Data sets from our study and Churchill and Riner's
conform, in some respects, to Setchell's (1929) original temperature
hypothesis. Setchell suggested that 15°C was the temperature required for
anthecis. In the Chesapeake Bay Z_. marina beds, anthesis was observed when
temperatures were nearly 15°C while in New York populations, anthesis started
shortly after the water temperature had exceeded 15°C. Setchell as well as
Tutin (1938) also suggested that above 20°C, flowers and immature fruits die
and slough off the plant. In the Chesapeake Bay, water temperatures were
over 20°C for one week before the peak of seed production (10-28 May) with
temperatures reaching 23-25°C during the peak of seed production. In New
York anthesis occurred primarily while the water temperature fluctuated
between 20-21°C. Due to inherent variation in populations of a species along
gradients of either depth or latitude, that the differences observed here and
in New York may not be significantly different. However, differences between
North American west coast populations (e.g. Puget Sound where water
temperatures do not exceed 15°C and flowering occurs at 8-9°C (Phillips,
1972), and east coast populations are undoubtedly significant. This latter
contrast suggests either temperature adaptation of west coast species or thj
effect of other factors in floral development.
In our study, we found that the period from initiation of pollen release
to initial seed development and release was 28-30 d. These results are
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similar to the findings of Churchill and Riner (1978) for New York
populations. DeCock (1980) also noted a similar length of time for pollen
release to seed development, for populations of Zostera marina in the
Netherlands.
The generative shoots of Zostera marina populations studied along the
east coast of the U.S. develop in a distinctly different pattern than that
reported for European populations. There is basepetal development of
rhipidia along the shoot as compared to acropetal and synchronous development
found in France (Jacobs and Pierson, 1981) and the Netherlands (DeCock,
198la), respectively. The size of the generative shoot as well as both the
number of spadices and rhipidia is also less along the east coast of the U.S.
Although a number of factors including the availability of nutrients and
depth (Jacobs and Pierson, 1981) may affect the growth of the shoots,
certainly the prolonged periods of favorable summertime water temperatures
(maximum water temperature does not exceed 15°C) observed in the European
studies is an important factor to consider.
A distinct flowering period combined with the rapid dehiscence of seeds
observed in our Chesapeake Bay populations is similar to that observed by
Churchill and Riner (1978) for the New York area. In our study, for example,
pollination occurred during a three to four week period from mid-April to
mid-May. Again, the European studies show distinctly different results with
DeCock (1981a) and Jacobs and Pierson (1981) recording prolonged flowering
periods.
The question of what ultimately terminates the flowering process has
been alluded to in a number of recent papers. Both DeCock (1981a) and
Churchill end Riner (1973) speculated that nutrient stress nay play an
important part in the cessation of flowering. Churchill and Riner (1978)
indicated that because of the 20-21°C water temperatures observed during
anthesis in their study site it was unlikely that flowering was terminated by
unfavorable water temperatures. We submit however that their observations as
well as ours suggest that in many areas the Zostera marina populations have
adapted to different temperature regimes so that flowering may occur at
higher limits than the 20*C originally proposed by Setchell (1929). We feel
this adaptation could be a particularly important feature in those areas
where water temperatures reach or exceed 30*C during the summer. In a
similar manner, Z_. marina populations have been shown to flower in areas
where water temperatures never exceed 20°C, suggesting an adaptation to
flower at lower maxima (Phillips, 1972; Harrison and Mann, 1975; Jacobs and
Pierson, 1981).
Because of the importance of temperature in the life cycle of Zostera
marina especially the reproductive aspects, latitudinal comparisons of
populations should show a progression of stages in the reproductive cycle
(e.g. anthesis or seed release) as one moves aouth. This was initially
suggested by Setchell (1929) and later confirmed for the European coast [see
Table III, Jacobs and Pierson (1981)]. In addition to the Churchill and
Riner (1978) data for New York, we examined the available data for North
Carolina (the southern limit of Z_. marina on the east coast of North America)
(Dillon, 1971) and for a Nova Scotian population (Keddy and Patriguin,
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1978). We compared events such as first appearance spadix primordia and
occurrence of anthesis and mature fruits were noted for each of these areas
and the Chesapeake Bay (Fig. 3). The greatest uncertainty in the comparison
is associated with observation of the spadix primordia since this
determination depends on the frequency of collections and the detail of
examinations of each shoot (Dillon did not report on this aspect in his
study). Based on the data for these four studies, each reproductive event is
reported to have occurred earliest in the most southern location and at
successively later dates at more northern sites.
An important question arising from figure 3 is how does the length of
the flowering period and the rate at which water temperature increases affect
rhipidium and spadix production? We hypothesize that the longer more
favorable water temperatures prevail, and the slower the rise of ambient
water temperature to summertime maxima, the greater the production of i
rhipidia and spadices should be. Although data are not available for all of ]
the sites in Fig. 3, Churchill and Riner (1978) do report an average of 7.6
spadices per shoot in New York, which is greater than the averages reported
here. Jacobs and Pierson (1981) report an average of 20 spadices per shoot
for a Zostera marina population in Roscoff, France where water temperatures,
averaging 9-15 C, appear to provide a prolonged, favorable environment for
flower production.
Although temperature is an important factor in the timing of the
reproductive sequence, irradiance may also be important. Backman and
Barilotti (1976), based on the results of their light reduction experiments,
suggested the importance of irradiance for flowering while Jacobs and Pierson
(1981) noted that irradiance varies with latitude. We suggest that it may
share in the timing of Z. marina reproduction. Further experimentation is
necessary for elucidation of the relative influence both parameters have on
flowering.
In addition to the geographical comparisons of the timing of the
flowering processes, these same studies have also compared gross
morphological characteristics such as length of flowering shoots, number of
flowering shoots m~^, number of seeds produced, etc. (Setchell, 1929; Tutin,
1938; McRoy, 1970; Felger and McRoy, 1975; Churchill and Riner, 1978; Keddy
and I'atriquin, 1978; Jacobs and Pierson, 1981). Care must be exercised in
these comparisons. Morphological characteristics may vary within an area in
response to depth, irradiance, nutrients and temperature. Within site
variances may therefore actually be greater than between site variances when
comparisons are made over latitudinal and longitudinal gradients. Indeed,
differences even within one location can vary greatly from one year to the
next, thus further complicating comparisons of data sets from short duration
studies (one yr or less) and longer cerm studies. We collected information
on the phenology of Zostera marina over a 30-month period at the three sites
described here and at several other sites (Orth et al., 1981). Significant
differences were found between years for number, length and biomass of
reproductive shoots at the study sites, although the timing of flowering
events were similar each year.
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It was interesting to note that at the Vaucluse Shores site in 1979,
samples taken along the edge of the grass bed, which was being covered by a
migrating sand bar (Orth, et a!., 1979), had 26% of the shoots reproductive
as compared to 2% and 3% at two nearby sites of similar depths not impacted
by the sand bar. This large number of reproductive shoots was observed again
in 1980 as well as at another site where sand was also covering the leading
edge of the bed. The seagrass bed could be responding to stress (coverage by
sand) by producing more reproductive shoots and thus more seeds.
In sumnary, the reproductive events of Chesapeake Bay Zostera marina
populations appear to parallel events described from other study sites.
Evidence from our study and other sites along the east coast of North America
supports a latitudinal gradient hypothesis based on temperature. However,
the importance of irradiance is unstudied and should be a topic for future
work. A laboratory approach similar to DeCock's work (1980, 1981a, 1981b,
1981c) certainly suggests this technique as the best and most reliable for
examination of the individual and/or combined influences of temperature and
irradiance on this aspect of Z_. marina's life cycle. We feel that only
through a more thorough and rigorous experimental test of these determinants
will these hypothesis be accepted or rejected.
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REFERENCES
Backman, T. W. and Barilotti, D. C. 1976. Irradiance reduction:
Effects on standing crops of the eelgrass Zostera marina in a coastal
lagoon. Mar. Biol., 34:33-40.
Churchill, A. C. and Riner, M. I. 1978. Anthesis and seed production in
Zostera marina L. from Great South Bay, New York, U.S.A. Aquat. Bot.,
4:83-93.
DeCock, A. W. A. M. 1980. Flowering, pollination and fruiting in Zostera
marina L. Aquat. Bot., 9:201-220.
DeCock, A. W. A. M. 1981 a. Development of the flowering shoot of Zostera
marina L. under controlled conditions in comparison to the development
in two different natural habitats in The Netherlands. Aquat. Bot.,
10:99-113.
DeCock, A. W. A. M. 1981b. Influence of light and dark on flowering in
Zostera marina L. under laboratory conditions. Aquat. Bot., 10:115-123.
DeCock, A.W. A. M. 1981c. Influence of temperature and variations in
temperature of flowering in Zostera marina L. under laboratoy
conditions. Aquat. Bot., 10:125-131.
Dillon, C. R. 1971. A comparative study of the primary productivity of
estuarine phytoplankton and macrobenthic plants. Ph.D. Dissertation, U.
of North Carolina. University Microfilms Ann Arbor, Mich. 112 pp.
Felger, R. S. and McRoy, C. P. 1975. Seagrasses as potential food plants.
Pp. 62-74. j.n_ G. Fred Somers (ed.), Seed bearing halophytes as food
plants. Proc. of a conference at the University of Delaware. NOAA
Office of Sea Grant, Dept. of Commerce (Grant No. 2-35223).
Harrison, P. G. and Mann, K. H. 1975. Chemical changes during the seasonal
cycle of growth and decay in eelgrass (Zostera marina) on the Atlantic
Coast of Canada. J. Fish. Res. Bd., Canada, .2:615-621.
Jacobs, R. P. W. M. and Pierson, E. S. 1981. Phenology of reproductive
shoots of eelgrass, Zostera marina L., at Roscoff (France). Aquat.
Bot., 10:45-60.
Keddy, C. J. and Pacriquin, D. G. 1978. An annual form of eelgrass in Nova
Scotia. Aquat. Bot., 5:163-170.
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McRoy, C. P. 1970. On the biology of eelgrass in Alaska.
tation, University of Alaska, Fairbanks. 159 pp.
Ph.D. Disser-
Orth, R. J., Moore, K. A. and Gordon, H. H. 1979. Distribution and
abundance of submerged aquatic vegetation in lower Chesapeake Bay,
Virginia. U.S. E.P.A. Chesapeake Bay Program. Final Report
EPA-600/8-79-029/SAV1. 199 pp.
Orth, R. J., Moore, K. A., Roberts, M. H. and Silberhorn, G. M. 1981. The
biology and propagation of eelgrass, Zostera marina, in the Chesapeake
Bay, Virginia. Final Draft Report. U.S. E.P.A. Chesapeake Bay Program,
Grant No. R805953. 207 pp.
Phillips, R. C. 1972. The ecological life history of Zostera marina
L. (eelgrass) in Puget Sound, Washington. Ph.D. Dissertation,
University of Washington, Seattle, Wash. 154 pp.
Setchell, W. A. 1929. Morphological and phenological notes on Zostera
marina L. Univ. Calif., Berkeley, Publ. Bot., 14:389-452.
Taylor, A. R. A. 1957. Studies on the development of Zostera marina L.
II. Germination and needling development. Canadian J. Bot., 35:681-695.
Tutin, T. G. 1938. The autecology of Zostera marina L. in relation to its
wasting disease. NewPhytol., 37:50-71.
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CHAPTER 3
SEED GERMINATION AND SEEDLING GROWTH OF
ZOSTERA MARINA L.(EELGRASS) IN THE CHESAPEAKE BAY*
by
Robert J. Orth
a--d
Kenneth A. Moore
*Accepted for publication in Aquatic Botany.
Contribution No. 1047 from the Virginia Institute of Marine Science, College
of William and Mary
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ABSTRACT
Seed germination and seedling growth of Zostera marina L. were monitored
in the Chesapeake Bay in 1979 and 1980. Harvested seeds were placed in small
acrylic tubes at several sites representing the salinity range of Z_. marina
distribution. Seed germi.iation was first observed to occur first in late
September and continue through May with peaks in the fall and spring. The
majority of seeds that germinated (66%) did so between December and March
when water temperatures ranged from 0-10°C. There was no correlation between
sites (different salinity regimes) ana frequency of germination rates
indicating that salinity was not a major factor in the germination process in
this study. Additional information on seed germination was available for
seeds collected in 1977 and 1980 and subsequently monitored for germination
at only one site. These data were similar to germination frequency recorded
in 1979-1980.
Seedling growth was measured from individuals collected from an existing
Zostera narira bed. Seedlings were collected from November through May at
which time we could no longer distinguish seedlings from existing vegetative
stock. Growth was characterized by increased length of the primary shoot,
number of leaves per shoot and numbers of shoots per plant. Seedling growth
was initially slow during the winter months (water temperature j< 10*C) but
rapidly increased in the spring (temperatures > 10°C). The size range of the
harvested seedlings indicated that seed germination in the field probably
occurred from October through April, corroborating evidence from the seed
germination experiments.
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INTRODUCTION
One of the most significant events in the life cycle of seagrasses is
the production of seeds. Seed production, and those events related to this
process such as flowering, seed release, dispersal, seed germination and
subsequent growth of the seedling serve not only as a means of maintaining
genetic diversity but also as an important dispersal mechanism. Indeed,
dispersal of seeds to an unvegetated area may be the only significant
mechanism by which the area can become vegetated. Despite these important
functions, there is little information on seed germination in seagrasses and
the role that seeds play not only in the maintenance of existing beds but !
also in the recruitment and re-establishment of new seagrass aveas as
compared to vegetative reproduction.
Observations and quantitative studies on the biology of Zostera marina \
L. (eelgrass) in many different areas of the world indicate that Z. iaa> ina
undergoes a distinct sexual reproductive phase with the formation of seeds
and eventual seed release being the last stages of the flowering process _,,
(Setchell, 1929; Taylor, 1957; Churchill and Riner, 1978; Keddy and
Patriquin, 1978). De Cock (1980), in particular, provided a very detailed
account of the flowering and fruiting of Z_. marina in the Netherlands.
Although there was relatively little known about the fate of the seeds and
the seed germination process, previous studies have indicated that, in >..,...
general, germination of ^2. marina occurred at lower temperatures (5-15°C) \.-'
under both light or dark conditions and was higher at lower salinities - v
(10 °/oo) than at higher salinities (30 °/oo). In ddilion, there was v
apparently no dormant period between seed release a-1 seed germination --'"
(Setchell, 1929; Tutin, 1938; Addy, 1947; Arasaki, 1950; Phillips, 1972;
Orth, 1976; and Churchill, unpublished).
Zostera marina is the dominant seagrass in the i .esapeake Bay and, until
recently, was abundant in many of the shoal areas cf le Bay and its
tributaries (Orth, 1976; Orth and Moore, 1981a, b). L spite its past
abundance, relatively little was known on the biology of Z_. marina in the
Bay. Since 1978, a large scale, multidisciplinary research program has been
underway on the biology and functional ecology of Z_. marina in the Bay. One
aspect of this research, which is reported here, involved assessing the
timing of seed germination and seedling growth of Z_. marina under natural -,/
field conditions. The seed germination process has important implications in •'
the Bay because of the potential use of seeds and seedlings for the
re-establishment of recently denuded areas.
Study Sites
Eight sites within and adjacent to the Chesapeake Bay were used during
this study for seed germination experiments (Fig. 1). Five sites were
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MUMFORT ISLAND
CLAY BANK
GLOUCESTER POINT
VAUCLUSE SHORES
WACHAPREAGUE
BROWNS BAY
GUINEA MARSH
ALLENS ISLAND
Fig. 1. Location of field sites used for the seed germination experiments.
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located in the York River, proceeding from the nnuth of the York River at the
Guinea Marsh site, to Clay Bank, the most upriver limit where Zostera marina
formerly occurred. Additional sites were located in Mobjack Bay (Browns Bay)
and on the bayside (Vaucluse Shores) of Virginia's Eastern Shore. Table 1
shows the salinity ranges for each of the sites.
The Guinea Marsh, Browns Bay and Vaucluse Shores sites contained dense
beds of Zostera inarina, with R_up_pJ_£ maritirca (widgeon grass) also
co-occurring at the Browns Bay and Vaucluse Shore sites. Aliens Island was
very sparsely vegetated while the Gloucester Point, Mumfort Island, and Clay
Bank sites were unvegetated. The latter three sites and the Aliens Island
site were densely vegetated with Z_. marina in 1973 but the vegetation
subsequently declined in 1973 and 1974 (Orth et al., 1979). "L. marina has
not been present at the Wachapreague site during the recent past although
there is evidence of its presence prior to the wasting disease in the 1930"s
in the shallows behind the barrier islands near Wachapreague (Orth and Moore,
1981a, b). The Gloucester Point site was used for additional seed germinaton
experiments conducted in 1977-78 and 1980-81.
MATERIALS AND METHODS
Seed Collection
Mature seeds, determined by direct observation of developing embryos in
reproductive shoots of field populations of Zostera marina and vital staining
with tetrazoliurn red, were collected from established Z_. marina beds in May
and June, 1979. The method of harvesting involved snorkeling over a Z_.
marina bed at low tide, removing a reproductive shoot with attached seeds at
its base and placing the shoots in a fine mesh collecting bag (0.5 mm mesh).
All reproductive shoots from a particular collecting location were
transferred to a single nylon mesh bag (0.5 ram mesh) and held in running
seawater at our laboratory to allow adequate time for decomposition of the
spathe and shoot and subsequent release of the seeds. All material in the
nylon bag was washed thoroughly through a 2 mm mesh sieve to separate seeds
from most of the other material. Seeds passed through this screen but were
retained on a 1 mm mesh sieve. Seeds from each collection were then placed
in open, 4 liter containers and held in a running seawater tank until
initiation of the germination experiments.
Seeds were collected from three locations in the lower Bay at successive
intervals; the mouth of the York River off the Guinea Marshes (May 22, 30 and
June 12), Browns Bay (Kay 14 and 22); and Vaucluse Shores (May 23S 31 and
June 7) (Fig. 1). Repeated collections from the sites were made in an
attempt to maximize the harvesting of mature seeds. In further discussion of
these collections, they will be subsequently referred to in the following
notation: Guinea Marsh - GM1, 2, and 3 for each successive collection;
Browns Bay - BB1 and 2; Vaucluse Shores - VSl, 2, and 3.
Seed viability of each collection was tested using the vital stain
tetrazolium red (2.3, 5-triphenyl-2H-tetrazolium chloride) (Churchill and
Riner, 1978). Fifty seeds from each collection were placed in a 0.5%
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TABLE 1. SALINITY RANGE FOR EACH OF THE SITES USED DURING THE FIELD
SEED GERMINATION EXPERIMENTS.
Site
Wachapreague
Vauciuse Shores
Browns Bay
Guinea Marsh
Aliens Island
Gloucester Point
Mumfort Island
Clay Bank
77
Salinity o/oo
25-32
15-24
15-20
15-20
15-20
14-18
12-18
8-15
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solution of the stain. Seeds that exhibited a distinct pink staining of the
cotyledon and upper hypocotyl region after 48 hrs. were considered viable.
Seeds were collected at the Browns Bay Zostera marina bed in May of 1977
and 1980 in the above manner, placed in open 4 liter containers and held in a
running seawater tank at ambient temperature. These collections will be
referred to subsequently as BB 1977 and BB 1980.
Field Germination Tests
Replicate lots of 200 seeds from each designated collection in 1979 were
placed in small acrylic tubes (15 cm long, 2 cm inside diameter). Seeds from
the following collections were used in the field germination test: VS2, VS3,
GM2 and GM3. Perforated plastic caps were placed at each end of the tubes to
prevent seeds from washing out; these caps allowed some water exchange with
the surrounding medium. The tubes were anchored approximately 5 cm above the
sediment surface in water depths of 0.1 to 0.3 m at mean low water fMLW).
Tubes were never exposed at low tide. We chose this method of monitoring
seed germination as compared to examining large volumes of sediment for
germinated seeds in established beds of Zostera marina for several reasons.
First, it gave us the ability to use a large number of seeds in a small area.
Secondly, it allowed us to repeatedly observe each lot of seeds and to
determine within a relatively short period of time (2 weeks or less) when
these seeds germinate, and thirdly, it allowed us to observe germination
rates in areas with no existing vegetation. Table 2 shows the distribution
of the replicate seed lots from the different seed collection periods and the
time each tube was placed at the specific location. At the Gloucester Point
area, in addition to seeds being located in shallow water, replicate lots of
seeds were placed at a second, deeper water area (3 m, MLW).
The seeds in the core tubes at each site were checked at approximately
two week intervals for germination. At each sampling period, the tubes were
processed immediately on location by placing the contents of each core in a
small enamel pan with adequete water and examining the material carefully for
germinated seeds. The criterion for successful germination was an extension
of the cotyledon from the seed case. Seeds that had germinated were removed
from the pan, placed in a holding jar and when returned to the laboratory
wer-j located in a running seawater tank. All remaining ungerminated seeds
were carefully placed back in the tubes which were then reanchored. No more
than 30 minutes elapsed during the sampling procedure.
Seeds from the BB1 and VS1 seed collections were placed in 4 liter jars
helJ in aquaria with running seawater at our laboratory (also located at
Gloucester Point) and monitored for seed germination. Seeds collected in
1977 and 1980 were also monitored at our laboratory similar to the BBl and
VS1 collections.
Seedling Growth
In order to estimate seedling growth of seeds that had germinated in
established beds of Zostera taarina, monthly samples were taken at the Guinea
Marsh area from November 18, 1979, to May 19, 1930, for seedlings. Random
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TABLE 2. STATION LOCATIONS FOR THE SEED GERMINATION TEST AND DATES WHEN SEED TUBES
WERE PLACED AT EACH LOCATION FOR EACH SEED COLLECTION (WHERE TWO DATES
OCCUR FOR A COLLECTION, ONE REPLICATE WAS PLACED ON THE FIRST DATE, THE
OTHER REPLICATE ON THE SECOND DATE).
Browns
Guinea
Aliens
Bay
Marsh
Island
Gloucester Pt.
VS2
•"•(Aug.
•"•(Aug.
•"•(Aug.
++(Aug.
15)
15)
15)*
15)
VS3
++(Aug.
++(Aug.
++(Aug.
++(Aug.
GM2
9)
6)
6)*
7)
++(Aug.
++(Aug.
++(Aug.
++(Aug.
9
6
6
7
,15)°
,15)
,15)*
,15)
GM3
+(Aug.
+(Aug.
+(Aug.
+(Aug.
9)
6)
6)*
7)
shallow
Gloucester Pt.
deep
Mumfort Island
Clay Bank
Vaucluse Shores
Wachapreague
++(Aug. 14) -M-(Aug. 14) -n-CAug. 14)
+(Aug. 7)
++(Aug. 15) -M-(Aug. 7) -M-(Aug. 7,15)
•M-(Aug. 24) ++)Aug. 10) ++(Aug. 10)
++(Aug. 22) +-i-(Jul. 23) -n-Uul. 23, Aug. 2) +(Jul. 23)
•M-(Aug. 27) ++(Aug. 27) ++(Aug. 27)
+ - represents one core tube of 200 eelgrass seeds
* - the entire set of core tubes at this site was lost immediately after being placed
in the field. Additional core tubes with seeds were set out on Sept. 7. Since
there were no remaining seeds from the GM3 collection, this could not be
replaced.
- one seed tube from this collection was lost at the initiation of the experiment
and replaced on Sept. 4.
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samples of sediment with seedlings and older shoots were collected from the
bed and carefully washed free of sediment. Seedlings were identified by the
presence of the seed coat which usually was still attached to the primary
root, or if the seed was absent, by a sccrpioid base, indicative of an older
seedling (Setchell, 1929). After the May samples, however, growth of these
seedlinjs had become so vigorous that seedlings could not be distinguished
from the previously established vegetative stock. Twenty-five seedlings from
each monthly collection were measured for maximum length of the primary leaf
(measured from base of cotyledon sheath to tip of primary shoot), number of
shoots per seedling and total number of leaves per seedling.
RESULTS
Seed Germination
Monthly and cumulative seed germination data at each of the eight sites
(nine collections) are shown in Fig. 2 (seeds from the VS2 collection did not
germinate and were not included in these calculations). Water temperature
data, superimposed on each graph, were obtained from a continuous temperature
recorder located at Gloucester Point. This provided a more accurate
representation of temperature variation in the region than spot measurements
obtained at each sampling site. These temperature data were used for all
sites except Wachapreague, where continuous temperature data recorded from
this site were used.
In most cases, the germinating seeds had reached a stage where there was
extension of the cotyledon and basal hypocotyl froa the seed coat, with
various lengths of elongation of the cotyledon. Some individuals had marked
extension of the plumule from the cotyledon sheath. No significant
development of root hairs on the basal hypocotyl were observed.
Data for seeds germinated (percent and cumulative percent) in the 4
liter jars held in running water for the BBl, VSl, BB-1977, and BB-1980
collections are shown in Figure 3 along with temperature patterns for the
seed gemination period.
Seeds from the BB2 and CMl collections in addition to VS2 produced no
germinated seeds and were not included in the analysis. Seeds from the GM2
collection had a low germination rate and these data were also not presented
here.
There was no significant correlation (p>0.05) between the percent
germination at the test locations and salinity (Fig. 2) (Spearman's rank
correlation test, rs, Siegal, 1956). Germination of seeds at Clay Bank
(38.6%) which is the upriver limit of Zostera marina growth and where
salinities ?veraged 12 °/oo is only slightly higher than seeds held at the
Uachapreague ('23.8%) area where salinities average 30 °/oo.
Seed germination in our experiments (including seeds collected in 1977
and 1980) occurred in every month except June, July and August, the three
months with highest water temperature. Seed germination was first observed
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\ -—Temperature /
GLOUCESTER POINT
Shallow
i i T i r
SONDJ FMAMJ
1979
1980
1979
1980
-20
-10
r-30
GLOUCESTER POINT
Deep
SONDJ FMAMJ
Fig. 2. Percent (bars) and cumulative percent (•—•) of seeds germinating each
month from September 1979 to June 1980, plotted against water temperature
(. .) for aj_i_ field sites.
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40-i
35-
30-
25-
20-
15-
10-
5-
0
VAUCLUSE SHORES
FLr,
40-
35-
30-
25-
20-
15-
10-
5-
0
BPOWNS BAY
SONDJFMAMJ
1979
I960
Fig. 2 (continued)
WACHAPREAGUE
Temperature
'J
-f—-\—i—i r
CLAY BANK
-r i—i—T—i—i r T i r
SONDJFMAMJ
1979
1980
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rlO
r30
1-20
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40-,
-30
SONDJFMAMJ
1979 1980
SONDJFMAMJ
1979 1980
Fig. 2 (continued)
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in a small proportion of the seeds in September and continued through May of
the following year. Seed germination in September and May were very low, and
at many sites no germination was recorded during these two months.
In the 1979 field test, tlie major period of seed germination occurred
between December 1 and March 31, when 66% cc the seeds germinated. Water
temperatures ranged from 0 to 10°C during chese four months. Every site
except Vaucluse Shores had the greatest number of seeds germinate in March
(37% of all germinated seeds). Forty-five percent of the total germinated
seeds were found through February when water temperatures reached a minimum
with the retaining 55% germinating after February as water temperatures
increased.
In the remaining two 1979 seed collections and 1977 and 1980 seed
collections from Browns Bay, the majority of the seeds that germinated did so
in the four month period between Dec. 1 and March 31 (BBl-66%; VSl-65%; BB
1977-90%; BB 1980-57%).
Two trends in the pattern of seed germination were observed. In the
first, germination increased initially in the late fall-early winter,
declined in mid to late winter and then increased again in the early spring
(Vaucluse Shores, Browns Bay, Clay Bank, Guinea Marsh, BB-1977, and BB-1980).
In the second, germination was low in the late fall-early winter period,
increased in the mid-winter period and reached a maximum during the early
spring (Wachapreague, Gloucester Point (both locations), Muinfort Island, and
BBl). The VS1 collection was different from all others as 7/% of the seeds
germinated between November and January. However, when data from all test
sites used in 1979 are combined, seed germination was constant through
February with March having the highest frequency (Fig. 2).
Seedling Development
Data on the number of leaves and shoots per seedling ind the lengths of
the primary shoots are given in Figure 4. The initial samples taken on
November 28 were most likely germinated in late October or early November,
since no seedlings were observed in the area or were present in samples taken
in mid-October or earlier. This first evidence of seedlings coincides with
the initial period of seed germination observed in our field experiments on
seed germination periodicity. By our last sampling date on May 19, the
seedlings were difficult to distinguish from vegetative shoots growing from
previously established rhizome stock. The lengths of the primary shoots of
the seedlings were very similar to the lengths of the vegetative shoots
measured for non-seedlings. By June the growth and intertwining of the
rhizomes of the seedlings and non-seedling made it impossible to separate one
from the other.
Seed germination appeared to be contributing additional seedlings to the
area from November to April. During November, 100% of the seedlings sampled
could be characterized as being of 8 cm or less in length with only one shoot
of two leaves with one primary and two adventitious roots. On the four
sampling dates from January to April, respectively, 35%, 35%, 20% and 16% of
the seedlings were of similar developmental stage. In November, 68% of the
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seedlings had their seed coats still attached to their primary roots. From
January to April, respectively, 481, 481, 242 and 02 of the seedlings were
similarly observed.
Growth of older seedlings was apparent throughout the winter period as
evidenced by the increasing size range with time of the data presented in
Figure 4. During April, for example, although newly sprouted seedlings were
still present, the largest seedlings had up to six shoots with over
twenty-five leaves. This was the result of possibly five months of growth.
DISCUSSION
In the Chesapeake Bay region, it is evident from both the seed
germination experiments and the pattern of seedling development that Zostera
marina seeds released during May and June begin germinating in the fall,
approximately four months later. In addition, this germination process
continues throughout the winter into the spring. It also appears that seeds
can germinate at least one year after release.
We suggest that the period between seed release and the onset of the
germination process in the field is a dormancy induced by high water
temperatures. We found virtually no germination when temperatures were above
20*C. Germination was first noted in the fall when temperatures dropped
below this level and ended in the spring when temperatures rose again to this
point. Germination was most rapid between 5 and 10*C. Our hypothesis is
supported by *~he results of a seed germination experiment conducted in 1977
(unpublished data). Seeds held in 20*C water from September to May never
germinated and eventually rotted while 70% of seeds held in seawater
subjected to ambient water temperatures germinated during this same period
(see Fig. 3, BB-1977 collection).
Additional evidence for the lack of an inherent dormant period other
than that induced by high temperatures is available from data on the pattern
of seed germination in Zostera marina beds along the east coast of the United
States. Data from Addy (1947) and Churchill and Riner (1978) and Churchill
(unpublished) indicated that there is a decreasing time period between seed
release and seed germination with increasing latitude.
In New York (41*,40'N) where seeds are mature and released in July, one
month later than in the Chesapeake Bay (37*, 2.5'N) (Churchill and Riner,
1978; Churchill, unpublished; Silberhorn, et al., unpublished) seeds begin
germinating three months after release compared to four in the Bay. In
Massachusetts (43*, 40'N) where seeds are released in late July and August,
Addy (1947) observed seed germination in the early fall, with little or no
dormant period. Although data are not available on seed germination in North
Carolina JZ. marina beds, the most southern limit of Z. marina distribution on
Jthe east coast of the United States, we could expect a longer dormant period
; between seed release and seed germination. Seed germination would be
expected to begin later in the fall than that observed in the Chesapeake Bay
t" since lower temperatures would occur later than when recorded in the Bay.
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Jacobs and Pierson (1981) noted that flowering in European Zostera
marina beds occurred later in more northern latitudes. Based on these
observations and data from the East Coast of the United States presented
here, we predict that in European Z_. marina beds the period between seed
release and initial seed germination would decrease with increasing latitude.
Our suggestion that water temperature is the primary variable affecting
seed germination is corroborated by data from Long Ieland Sound (Churchill,
unpublished) and additional evidence from the Chesapeake Bay (Orth, 1976).
Others, however, have suggested that low salinity is a factor controlling
germination (Arasaki, 1950; Phillips, 1972; Lamounette, 1977). Their
conclusions are not confirmed by our field experiments where we found no
salinity effect among our sites representing the range of salinities where
Zostera marina has grown or is growing in the Bay (10-25 °/oo). However,
under natural field conditions, the seed germination process probably
represents an integration of a number of variables that may act
synergistically or antagonistically. Thus, salinity effects may not be
expressed with seeds germinating in the field.
The results reported here contrast with earlier work of Orth (J976) and
Churchill (unpublished) where seed germination was reported to occur
primarily in the fall. There may be other yet unidentified factors that
could influence the timing of seed germination, as well as inherent
differences between different populations of Zostera marina, which may be a
result of adaptations to local conditions. It is obvious from the above that
only through a more detailed and extensive experimental program studying
various combinations of factors, will it be possible to define more
accurately the germination ecology of Z. marina (e.g. see Van Vierssen, 1982,
on the germination ecology of Zannichelia).
One of the problems we encountered with our seed germination wa?i the
lack of germination in some of the seed collections, e.g. VS2. This may be
related to our initial method of holding the reproductive shoots un';il seeds
are released. Those collections which produced small numbers of viable seeds
had large amounts of decomposing material packed in the mesh bags. There may
have been some factor that affected the viability of the seed in t'.iese bags,
especially while the shoots decomposed, as the largest seed collections had
the lowest germination rates. In order to avoid this potential pioblem, when
collecting reproductive shoots for seeds, we recommend placing them in open,
running water systems to allow for adequate water circulation and removing
the decomposing shoots soon after seed release.
The length of the primary shoots of the seedlings we observed on
November 28 gives an indication of the significant growth that occurs in
seedlings in the fall in the Chesapeake Bay region, as the average length was
6.1 cm. We also observed vegetative growth of new shoots from existing
rhizome stocks during the first part of October (Orth et al., 1981 \
Comparisons of plumule (i.e. shoot) lengths of seedlings from Long Island
(Churchill, unpublished) and the Chesapeake Bay indicates the more rapid
growth of the seedlings in the more southern Chesapeake Bay area as seedlings
were larger during comparable time periods. Although Churchill reports
little plumule growth between December and March, we observed an increasing
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number of seedlings with both secondary and tertiary shoots during this
period, many over 12 cm in length. Rapid growth in Chesapeake Bay seedlings
in the spring resulted in shoot lengths averaging 24 cm as compared to 13 cm
in Long Island for the same time period. Churchill does not present
temperatures data, but we assume that Zostera marina beds in the Bay will
experience slightly warmer temperatures than New York Z. marina beds during
this period. Setchell (1929) reported on seedling growtn for plants obtained
from Marin County, California from their germination in February through
October. Data on changes in leaf length and number of shoots were not
presented, but his figures depicting seedling growth were similar to our
observations.
Seed germination and the subsequent growth of seedlings can have
important implications in not only maintenance and persistence of the
existing bed, but also in the re-establishment of denuded areas.
Observations and direct sampling of a section of a Zostera marina bed at the
Guinea Marsh area indicated a substantial contribution to the regrowth of
this section fay seedlings compared to the production by existing vegetative
stock (Orth et al., 1981). In addition, observations of an unvegetated area
near an existing Z. marina bed at Aliens Island showed initial recruitment
was extensive and occurred primarily from seeds and subsequent rapid seedling
growth after germination. Denuded area? at more distant sites from vegetated
areas have not shown any evidence of revegttation, most likely because of the
lack of propagules reaching them.
Thus, it appears that the value of the reproductive process in
revegetation of denuded areas can be significant. However, the pattern, rate
of recovery and analysis of factors controlling this revegatation demand
further study.
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REFERENCES
Addy, C. E. 1947. Gemination of eelgrass seed. J. Wildl. Manag..
11:279.
Arasaki, M. 1950. Studies on the ecology of Zostera marina Zostera
nana. Bull. Jap. Soc. Fish., 16:70-76.
Churchill, A. C. and N. I. Riner. 1978. Anthesis and seed production
*n Zostera marina L. from Great South Bay, K»w York. Aquatic
Bot., 4:83-93.
De Cock, A. W. A. M. 1930. Flowering, pollination and fruiting in
Zostera marina L. Aquat. Bot., 9:201-220.
Jacobs, K. P. W. M. and E. S. Pierson. 1981. Phenology of
reproductive shoots of eelgrass, Zostera marina L., at Roscoff
(France). Aquatic Bot., 10:45-6Q~
Keddy, C. J. and D. G. Patriquin. 1973. An annual fora of eelgrass
in Nova Scotia. Aquatic Bot., 5:163-170.
Lamounette, R. 1977. A study of the germination and viability of
Zostera marina L. seeds. M.S. Thesis, Adelphi Univ., Garden
City, NY, 41 pp.
Orth, R. J. 1976. The demise and recovery of eelgrass, Zostera
marina in the Chesapeake Bay, Virginia. Aquatic Bot., 2:141-159.
Orth, R. J. and K. A. Moore. 1981a. Submerged aquatic vegetation in
the Chesapeake Bay: past, present and future. Proc. 46th North
American Wildlife and Natural Resource* Conference. Wildlife
Management Institute, Washington, D.C., pp. 271-283.
Orth, R. J. and K. A. Moore. 1981b. Distribution and abundance of
submerged aquatic vegetation in the Chesapeake Bay: a scientific
perspective. Virginia Institute of Marine Science, Special
Report in Applied Marina Science and Ocean Engineering No. 259.
42 pp.
Orth, R. J., K. A. Moore and H. H. Gordon. 1979. Distribution and
abundance of submerged aquatic vegetation in the lower Chesapeake
Bay, Virginia. U.S. EPA Final Report. Chesapeake Bay Program.
EPA-600/8-79-029/SAV 1. 219 pp.
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Orth, R. J., K. A. Moore, M. H. Roberts and G. M. Silberhorn. 1981.
The biology and propagation of eelgrass, Zostera marina in the
Chesapcike Bay, Virginia. Final Report, U.S. EPA Chesapeake Bay
Program, Grant No. K8059S3. 207 pp.
Phillips, R. C.. 1972. Ecological life history of Zostera marina L.
(eelgrass) in Puget Sound, Washington. Ph.D. Dissertation, Univ.
of Washington, Seattle, 154 p.
Setchell, W. A. 1929. Morphological and phenological notes on
Zostera marina L. Univ. Calif, Berkley, Publ. Bot., 14:369-/»52.
Siegal, S. 1956. Non-parametric statistics for the behavioral
sciences. McGraw-Hill, New York. 312 pp.
Taylor, A. R. A. 1957. Studies of the development of Zostera
marina L. II. Germination and seedling development. Canadian J.
Bot., 35:681-695.
Tut in, T. G. 1938. The autecology of Zostera marina in relation
to its wasting disease. New Phyt., 37:50-71.
V«n Vierssen, V. 1982. The ecology of communities dominated by
Zannichelia taxa in western Europe. I. Characterization and
antecology of the Zannichelia taxa. Aquat. Bot., 12:103-155.
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CHAPTER 4
TRANSPLANTATION OF ZOSTERA MARINA L. INTO RECENTLY DENUNDED AREAS*
by
Kenneth A. Moore
and
Robert J. Orth
* Results of fertilizer experiment at Aliens Island will be published in the
Proceedings of the Nineth Annual Conference on Wetlands Restoration and
Creation, Hilisborough Community College, Tampa, FL. May 20-21, 1982
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ABSTRACT
Zostera marina was transplanted to a total of five sites during 1979
and 1980 along the York and Rappahannock Rivers in areas which contained
extensive stands of submerged vegetation prior to 1973. The use of whole
plugs including sediments and rhizoaes had significantly greater success
than a method where shoots were woven into biodegradable mesh and placed
on the bottom. Cost per acre were estimated at $8,000 to $42,000 per acre
respectively for the two methods using 0.6 m spacing. Survival of the
transplants appeared directly related to site location with the most upriver
sites having the most rapid and severe failures. Transplants at the donor
site adjacent to the existing vegetation had excellent survival using the
plug method. Transplantation during the spring, summer and fall seasons,
demonstrated best long term survival during the fall, and poorest during
the summer. Regardless as to when planted all the transplanted vegetation
demonstrated the greatest rate of decline during the months of July and
August. This may be related to high water temperatures, increased turbidity
and epiphytic growth. Dieback began first in the most upriver locations.
The subsurface application of a slow release fertilizer at transplanting
time significantly increased both the survival and growth of the transplanted "" ~/-
vegetation. A quick release fertilizer had no significant effect. ^'
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INTRODUCTION
Zostera marina L. (eelgrass) is the dominant specie: of vegetation found
in the mesohaline, southern half of the Chesapeake Bay (Orth et al., 1979).
Along with a companion species Ruppia maritima (widgeon grass), this species
forms extensive meadows throughout many portions of the lower Bay shoreline
and its major tributaries (Orth et al., 1979). These ^. marina dominated
beds, as with other submerged grass systems throughout the world, ire
considered an important component of estuarine and coastal ecosystems
(Phillipf,, 1974a; McRoy and Helfferich, 1977; Thayer and Phillips, 1977;
Phillips and McRoy, 1980; Phillips, 1980a, 1980b).
In addition to their resource value, the physical presence of seagrass
beds helps to stabilize sediments and protect the adjacent shore lands from
erosive events (Ginsburg ar-d Lowenstam, 1958; Zieman, 1972; Eleuterius,
1975). The importance of a seagrass bed as a preventive mechanism for
substrate erosion has best been shown in areas where the seagrass bed was
removed. Wilson (1949) and Rasmussen (1973) describe shore conditions before
and after the Jemise of Zostera marina in the 1930's. Wilson (1949), working
in England, indicated a lowering of ground level of 2 feet or more due to the
erosion of the sand where the JJ. marina had died. A stone layer beneath the
original sand layer became exposed after the removal of grass and sand, and
was colonized by seaweed. Raomussen (1973), working in Denmark, showed that
beaches covered with Z. marina underwent similar changes. There was a
general lowering of the shore with exposure of a stone layer and coarser
sediments prevailing where fine sediments once dominated. The disappearance
of Posidonia beds in France due to pollution (Maggi, 1973) resulted in
extensive erosion of the bottom substrate and shoreline. A shel) layer which
was under the grass bed eventually became exposed and was washed shoreward.
There was a loss of 15 cm to 30 cm of sediment in an area in the York River,
Virginia, where "L_, marina was removed by cownosc ray activity (Orth, 1975).
Although submerged vegetation can in many cases absorb some extreme
environmental events such as hurricanes (Oppenheimer, 1963; Thomas et al.,
1961), they are susceptable to both natural and man made perturbations
(Duncan, 1933; Renn, 1936; Odura, 1963; Tha; er et al., 1975; Orth, 1975; Orth,
1976; Rasmussen, 1973, 1977; Phillips, 1980b). Increased utilization of the
coastal zone, especially in the United States, has led to increased demands
to be placed upon existing beds of submerged aquatic vegetation and
subsequently a desire to ameliorate or mitigate losses of vegetation where
possible.
In recent years there has been a resurgence of interest in
transplantation of seagrasses. Earliest documented efforts (Addy, 1947a,b)
were prompted by a desire to restore areas of Zostera marina that had been
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greatly reduced by the "wasting disease" phenomenon of the early 1930's
(Tutin, 1938). More recently efforts have been concentrated on transplanting
several dominant species of vegetation, Z. marina, Halodale wrightii,
Thalassia testudin-ja, and Syringodium f iliforuie. Studies have investigated
different procedures for transplanting and anchoring these seagrasses (Kelly
et nl., 1971; Phillips, 1972; van Breedveld, 1975; Thorhaug and Austin, 1976;
Phillips, 1974b; Phillips, 1980a,b), as well as attempting to mitigate actual
losses of vegetation caused by dredging and othei botton. disturbing
activities (van Breedveld, 1975; Robilliard and Porter, 1976; Churchill et
al., 1978; Phillips et al., 1978; Fonseca et al., 1979).
Although there have been a number of studies dealing with the
transplantation of marine grasses there nas been no recently reported work in
the lower Chesapeake bay region, especially in areas once dominated by
Zostera marina. A recent study of the distribution and abundance of
submerged vegetation in the lower half of the Chesapeake Bay and its
tributaries (Orth et al., 1979) has confirmed earlier observations (Orth and
Gordon, 1975; Orth 1976) that there has been a considerable decline in
vegetation in many areas since approximately 1973. Losses of vegetation have
been particularly severe within Virginia's tidal tributaries, especially the
York, Rappahannock and Potomac rivers where large beds dominated by Z. marina
that previously extended up to 30 km from the river's mouths are now
completely gone. This decline apparently occurred within a two year period
and at the initiation of this study in 1979 there appeared no evidence of
natural revegetation.
Because of the v&lue of the submerged grasses, and the lack of natural
revegetation of these denuded areas and interest by the public in
transplanting grasses into the barren areas, this project was proposed to
assess th<_ feasibility of transplanting wild plants of Zostera marina using
existing techniques in order to revegetate selected pilot areas within
Virginia's tidal rivers. Factors such as time of year of transplantation,
location and depth of sites, survival and growth of transplants, and effects
of fertilizers en success were to be investigated. In addition to its value
as a management tool, transplantation of "L_. marina into presently denuded
regions can provide insight into limiting factors controlling the natural
revegetation of thase areas and indicate whether the original declines mp.y
have been due to episodic or chronic conditions.
MATERIALS AND METHODS
Spring Transplanting Effort (1979)
The initial transplantation effort began in March 1979. The primary
goal of this effort was to test the feasibility of transplanting Zostera
marina in the Chespapeake Bay usin£ two methods for transplanting whole
plants" (Thorhaug and Austin, 1976; Addy, 1947; Phillips, 1974, 1980; Fonseca
and Kenworthy, 19V9). In the first method, developed by Fonseca and
Kenworthy (1979) and successfully utilized in a mechanically disturbed Z_.
marina area in North Carolina in the fall of 1978, whole plants were removed
by shovel from an established bed located at the Guinea Marsh area near the
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raouth of the York River in Virginia. The piarts were transported in water to
the lab where vegetative shoots with the associated sections of rhizomes were
separated from the reproductive shoots. The rhizomes with the attached
vegetative shoots were then woven into precut 20 cm x 20 cm squares of
biodegradable marsh paper (Koldgro manufactured by Gulf States Paper Corp.,
Alabama) at a density of approximately 10 shoots per square and stored in
running s.awaler until planted.
In the second method, 10 cm diameter plugs including whole plants, roots
and rhizomes and associated sediment to a deptu of 10-15 cm, were removed by
the use of plastic coring tubes from the same established grass bed. The
individual plugs were immediately placed in small plastic bags and stacked in
insulated plastic coolers for transportation to the transplant site. Wet
burlap was layered with the plugs to keep the Zostera marina shoots moist.
The transplant site selected co receive both the plugs and mats was
located in the Mumfort Island area of the York River (Fig. -.) approximately
13 km upstream from the river's mouth. This area was selected for the
following reasons: until 1973 it was the site of extensive eelgrass beds
(Orth et al., 1979) and was the location of intensive studies on the epifauna
and infauna of Zostera marina beds (March, 1970, 1973, 1976; Orth, 1973); the
area is presently devoid of Z_. marina (Orth et al., 1979); the site is
relatively isolated and mainimum human disturbance was expected.
At the Mumfort Island site a total of eight treatments were used in
transplanting (Table 1). Each treatment consisted of 42 mats or plugs of
Zostera arranged in a 6 x 7 array with two root (61 cm) centers (Fig. 2).
Two locations were selected within what had been determined by archival
aerial photography to be the previous bed outlines. The first was an inshore
area approximately 150 m from the largest island (depth, 0.5 m at MLW) and
the second an offshore area 300 m from the island (d»pth. 1.0 m at MLW).
These are representative of the depths at which Z_. marina is generally found
around the lower Chesapeake Bay (Orth et al., 1979). At each location the
four treatments consisted of two arrays of plugs and two of mats, one of each
method fertilized at planting with commercially available ammonium nitrate
(34-0-0) and one left unfertilized.
The plugs of Zostera marina were implanted by overlaying a large (10 x
12 ft) grid on the shallow bottom to locate the planting sites. Using a
coring tube, a 10 x 15 cm plug of sand from the unvegetated bottom was
removed at the appropriate 2 ft (61 cm) spacing, 25 g of fertilizer added
into the hole (for fertilizing treatments only) and the plug of Z_. marina
with roots and rhizomes and attached sediment inserted. Care was taken to
insure fhat the Z_. marina was planted at the correct depth. Each plug was
then marked with a small orange stake.
Each Z_. marina mat was placed on the bottom at the correct spacing and
anchored into the sediment with U-clips. In the fertilized treatments, 25 g
of fertilizer were spread over each of the mats. Finally, each mat was
marked with a small orange stake.
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GP- Gloucester Point
Ml- Mumfort Island
PI - Parrot Istor.d
GM- Gjinao Marsh
Al- Aliens Island
Fig. 1. Map of lower Chesapeake Bay showing locations of transplant sitet,.
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Fig. 2. 6x7 array of Zostera narina plugs.
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For coopf.rison of the time and effort needed for each of the methods
accurate records were maintained of che cian-houis required for transportation
to or from the sites. This included digging up the stock and obtaining the
cores, preparing the mats, and planting the mats and plugs. The transplanted
material was then c_alitatively observed for growth and survival of
transplants. Temperature, salinity and secchi disk measurements were
routinely made.
Suarner Transplanting Effort (1979)
A second transplanting effort was initiated in early June (Table 1). It
coincided with increasing water temperatures (15 to 20*C) and near maximum
standing stock of Zostera taarina. Based on results obtained from the spring
transplanting effort, several changes were made. First, only the plug method
of transplanting was undertaken. Second, in addition to the Mumfort Island
location four other sites received Z. gar ina transplants. Three of these
sites were located along the northern shoreline downriver from the Mumfort
Island area while one was located along the Rappahannock River. The first
additional site vas at the Cuinea Marsh area (Fig. 1) immediately adjacent to
where the donor plugs were obtained at the mouth of the York River. This
site consisted of a large patch of unvegetated sandy bottom surrounded by a
dense Z. marina bed. The second site was located approximately 5 km upriver,
and was adjacent to an area of Spartina alterniflora dominated marsh known as
Aliens Island. Until 1973 this shallow littoral area was heavily vegetated
with Z_. marina but today only « few isolated patches of grass remain adjacent
to the island's shoreline. A third area was located near the VIMS laboratory
at Gloucester Point approximately 5 km upstream from Aliens Island and 5 km
downstream from Mumfort Island. Here too, a dense bed of Z. marina recently
existed (1973) but today no vegetation is found. Approximately 2 km
downriver from Gloucester Point the most upstream patches of Z. marina are
currently found. A fourth transplanting site was located in the vicinity of
Psrrotts Island or. the Rappahannock River. As with the other sites it was
vegetated with Z. marina until the early 1970's, but today is devoid of
submerged aquatic vegetation.
At each of the four new transplanting sites only one depth zone was
planted. This was approximated 0.7 m below MLW and represented the median
depth at which Zostera marina is found around the lower Chesapeake Bay. Both
the 0.5 m and 1.0m below MLW zones were continued at the Mumfort Island
site.
Each of these six locations (two at the Mumfort site, one at each of the
rest) received two treatments of 6 x 7 arrays of Zostera marina plugs. One
treatment was fertilized with ammonium nitrate and one left unfertilized.
The plugs were transplanted in a manner identical to that described for the
spring transplanting effort. Growth or decay of transplants was followed by
monitoring percent survival of plugs as well as the numbers and lengths of
shoots in the surviving plugs. Temperature and salinity measurements were
made at each visit to the sites as were secchi disk readings when water
depths were greater than the secchi depth.
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Fall Transplanting Effort (1979)
A third transplanting effort was initiated in September and October 1979
(Table 1). This period was chosen to correspond to decreasing water
temperatures (25 to 20*C), and increasing water clarity (secchi 1.0 to
1.7 m). In addition, it occurred after the annual late summer period of
senescence of Zostera marina, which is characterized by high water
temperature, high turbidity (secchi 0.5 to 1.0 m) and heavy epiphytic growth
on the Z_. marina leaves.
Methods employed in this fall transplanting effort followed very closely
those utilized during the summer period. At one depth at each of five sites
(Guinea Marsh, Aliens Island, Gloucester Point, Mumfort Island, Parrott
River) two 6x7 arrays of Zostera marina plugs were transplanted. One
treatment was fertilized with ammonium nitrate and one was unfertilized. The
plugs were transplanted in a manner identical to that of the spring and
summer transplants and located immediately adjacent to the existing summer,
1979 arrays. Growth or decline of the transplants was followed by monitoring
percent survival of total number of plugs as well as the number and length of
turions in the surviving plugs. All five areas were transplanted in
mid-October, 1979. The Aliens Island site was transplanted with two
additional fertilized and unfertilized arrays in mid-September 1979 to
further investigate an optimum time for transplanting Z_. marina in this
region of the Chesapeake Bay. Temperature, salinity and secchi disk readings
were routinely obtained.
Spring Transplanting Effort (I960)
A fourth transplanting effort was initiated in April 1980 (Table 1).
This period was chosen for comparison with the spring 1979 transplanting
effort and corresponded with increasing water temperatures and rapid growth
of Zostera marina. All four sites along the York River (Guinea Marsh, Aliens
Island, Gloucester Point, Mumfort Island) were transplanted with
unfertilized, 6x7 arrays of "i. marir.a plugs at one depth (0.7 m) which were
placed adjacent to previously transplanted (Fall, 1979) arrays. The Parrotts
Island site on the Rappahannock River was omitted from this effort in order
to concentrate investigations on the range of sites available on the York.
As a result of the findings of the 1979 transplanting effort, th.- number
of fertilized transplants were reduced in spring 1980. However, to continue
the investigations of the effect of fertilizers on the survival and growth of
transplanted Zostera marina as well as to investigate the fate of these
fertilizers after application, several studies were initiated.
In March 1980 replicate sediment cores were obtained prior to
transplantation in the unvegetated bottom at each of the four transplant
sites along the York River (Guinea Marsh, Aliens Island, Gloucester Point,
Mumfort Island) as well as the vegetated donor site at the Guinea Marsh.
These cores were obtained to compare the donor and recipient sites for any
differences in existing sediment-nutrient regimes.
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The cores were obtained by use of 5.0 cm (2") O.D. plexiglass core tubes
50 cm in length which were graduated on the side in cm. The tubes were
forced into the botton. to a depth of approximately 30 cm in the center of the
plugs, plugged with a rubber stopper and pulled from the bottom with the core
tube containing the sediment vegetation (if present) and the overlying water.
The individual tubes were capped at the bottom and placed in a covered
container filled with ambient temperature seawater. Immediately after all
the samples were taken the core tubes were returned to the lab within 30
minutes for extraction.
Upon return to the laboratory an individual core tube was unplugged and
an aliquot of the overlying water extracted using a large hypodermic syringe
with an attached 0.4 y glass fiber filter in a filter holder. The filter was
placed in a 50 ml plastic, conical certrifuge tube with screw cap and
immediately frozen for later analysis. The sediment plug was extruded from
the core tube onto a graduated holder and sectioned into 0-2, 2-5, 5-10 and
10-15 depth segments. Each section of plug sediment was placed in a Gelman
filter-centrifuge tube holder and centrifuged through a 0.45 u glass fiber
filter to extract the pore water. The filtered pore water was transferred to
a 50 ml capped centrifuge tube ard immediately frozen. The remaining
sediment fraction was frozen for later grain size analysis according to
procedure outlined in Folk (1961).
Pore water from each segment and the sample from the overlying water
were analyzed for NH^*, N03~, N2~ and P04~-* using automated analysis
techniques (EPA, 1974) with a technitron auto-analyzer. Modifications to
these techniques were made after Wetzel et al., 1979, including concentration
of nitrate/nitrite reagents, a two reagent chemistry for phosphate
determination and a two reagent chemistry for ammonia (Solorzano, 1969;
Koroleft, 1970; Gravitz and Gleye, 1975; Liddicoat, Tibbies and Butler,
1975).
In a similar manner half (21) of an unvegetated array of plugs at the
same location were fertilized with aaaonium nitrate and half (21) with
Osmocote. In this treatment 10 cm plugs of sediment were removed from the
bottca, 25 g of fertilizer wtre added, and the sediment plugs were replaced
in the same hole. The unvegetated plugs were then marked with small stakes
for later sampling.
At T (date of transplant) + 10 days, T + 37 days, two sediment cores
were obtained in each of the six treatments at the Aliens Island site:
Zostera marina plug + ammonium nitrate; Z_. uarina plug + Osmocote; 2. marina
plug unfertilized; bare sediment •«• ammonium nitrate; bare sediment •*•
Osmocote; bare sediment unfertilized.
Growth or decline of the transplants were followed as in previous
transplanting efforts by non destructive sampling methods for a period of 216
days by SCUBA or snorkel. At every sampling period each plug was exalined
for percent survival of the total number of plugs (undisturbed by the
nutrient sampling), numbers and densities of t-rions in the surviving plugs,
number of reproductive shoots and areal spread of the plugs. Temperature and
salinity measurements were made at each visit.
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Light attenuation was measured by use of a Li-COR PAR meter with cosine
collector beginning in June, 1980. Three to five PAR measurements were made
per day from 0800 to 1600 hours EST at each of the transplant sites at
approximately weekly intervals. Sampling runs initiated with the most
downriver site and proceeded upriver to minimize intersite tidal stage
variation. Davs when high or low slack periods approximated 1200 hours were
preferentially chosen. At each station light readings were obtained at
0.25 m intervals from the surface (just above the water's surface) t? bottom
(15 cir above bottom). The attenuation coefficient (Kd) was determined using
the surface and bottom readings. Kd was calculated by the function:
, E2
vj — ~*-n "~~~
~ El
(Z2 - Zj)
where In is the natural log, E2 is the it radiance at depth Z2, Ej is the
irradiance at depth Z\ and (22 - Zi) is the distance between the two depths
in meters. The units of Kd are m~*.
At the Gloucester Point site an attempt was made to assess the inpact of
the mud snails (Ilyanassa obsoletus) which were observed in the spring of
1979 to completely cover the transplanted plugs at the site. Replicate Iff.2
cages covered with 6 mm mesh screening but open at the top and bottom were
each placed around four transplanted plugs in March prior to the snail
infestation for approximately a three month period. They were regularly
cleaned of epiphytes and those few snails which managed to get inside the
exclosures were removed. Comparisons of the growth and survival were made
between the caged and the unprotected plugs.
RESULTS AND DISCUSSION
Spring 1979 Transplanting Effort
Transplantaion of four 6x7 arrays of Zostera marina (168 transplants)
by use of mats required 82.5 man hours of effort. In contrast, the
transplantation of an equal number of plugs required 16.0 man hours. These
equate to 2.0 transplants per man hour for the mat method and 10.5
transplants per man hour for the plug method. Both of these time and effort
measurements included all aspects of the transplantation process excluding
transportation time from the donor to the recipient site. Obviously the plug
method proved much more time effective than the mats. Most of this time
differential resulted from the tedious steps of having to weave the
individual "L. marina plants into the mat fabric. Planting time for each
method proved to be about equal, while harvesting the individual plugs
required more time than digging up and washing clusters of shoots with
entangled roots and rhizomes for the mat method.
Churchill «t si. (19/8) provide comparative time and effort data with
their use of miniplug transplants near Long Island, New York. In their
study, 26.6 miniplugs were transplanted per man hour frcm sites less than
one mile apart, so as to effectively negate transportation time. Other
studies (Ranwell, 1974; Fonseca et al., 1979; Phillips, 1980) provide more
difficult comparisons because data is provided in cost per area and costs of
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"7
'' * X -;--'
. V- ,-"-'- -
- F
labor and vessels vary from study to st'jdy and from year to year. Fonseca et
al. (1979) provide a table listing cost comparisons for different methods of
transplantations of Zostera marina for several published studies which range
from §0.009 to $0.27 cost per shoot. We calculate for our study using rates
of $5 per hour wages and §100 per day boat rental (the same costs as
Churchill et al. 1978) that our plug method would cost $0.07 per shoot and
our mat method §0.38 per sheer for 10 shoots average per mat or plug.
Fonseca et al. (1979) report costs of §0.086 per phoot for their comparable
mat method and projected costs of $0.028 by using improved weaving
techniques. The used an average of 15 shoots per mat.
Phillips (198('b) lists comparative costs of several published studies
which range from §1,645 to $76,545 per acre although the data used for the
latter figure has been questioned (Fonseca, personal cocxaunication). The
densities of the transplants vary greatly from study to study however. We
estimate costs per cere of approximately $8,000 and $42,000 per acre using
0.6 m spacing for the plugs and mats, respectively. This conpares with
Churchill et al. (1978) cost of $3,370 pe: acre using mini plugs in Long
Island.
In addition to the tine advantage of the plugging asthod in this «tudy
the plugs themselves with the associated sediment provided a stable anchor
for the Zostera marina plants in the highly exposed Mumfort Island location.
The Z, marina plants %;oven into the mesh of the suits, were hard pressed to
remain in position during periods of increased wave activity. Fonseca et al.
(1979) found that the raesh mats survived quite well after a fall 1978
transplanting in a _Z. marina area near Beaufort, North Carolina. However,
their site was much more protected than the Mumfort Island site in Virginia
and was surrounded by an existing Z_. marina bed.
Water temperature varied frooj 10 to 15*C curing this transplantation
effort in late March. Initially all the plugs and mats aopeared to be doing
quite well with an apparent difference between the fertilized &nd
unfertilized treatments. After a week however, the mats at both the 0.5 m
and 1.0 m depths at Mumfort Island began to be ripped apart by the high
energy or the waves and many of the individual turions were lost. The
Zostera marina plants trnsplanted in the plugs were much less affected by
storm waves and only a few shoots were lost. By mid-April it was apparent
that the mats were not holding up well. Not only were they affected by the
tidal currents and wind waves, but several were uprooted by the burrowing of
bluecraba (Callinectes sapidus). The plugs were also affected by the blue
crabs and several were lost by this burrowing activity. The habitat values
of these small areas of plants became obvious as the small transplants
immediately attracted numerous crabs, small fish and snails.
Churchill et al. (!' 78) similarly reported a greater loss of miniplugs
(shoots, roots and rhizomes with no sediment) when they compared thew to
plugs with sediment. They concluded however that in their area the greater
survival was not equal to the additional labor and time involved.
By mid-April the Zostera raarina plugs as well as the remaining mats had
become h-iavily infested with the mud snail, (Ilyanaasa obsoletus). This mud
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snail requires a hard substrate to attach its egg cases during its spawning
season. The overpopulation of the Z. marina turions was so great that the
entire surface areas of the leaves were completely covered with the
gastropods. On several occasions the snails were removed from the plants by
use of suction and numbers of over several hundred per 0.007 m^ plug were
recorded.
During the first week of Miy when the water temperature reached 20*C
most of the snails were absent from the Zostera marina shoots. However it
was at this tiae that Z_. marina rapidly began to deteriorate. Few shoots
remained in the transplanted mats but the plugs, which had looked quite
healthy the week before, appeared chlorotic in both the fertilized and
unfertilized treatments. By May 15 the 0.5 ra depth transplants had
experienced a significant dieoff of leaves and by the end of May all the
treatments had died off to such an extent that only a few shoots of Z. marina
remained.
Summer 1979 Transplanting Effort
Because of the poor success of the mats transplanted during the spring
of 1S79 and the much greater amount of man hours required for the technique,
only Zostera marina plugs with attached sediment were transplanted daring the
summer. Figure 3 presents the percent survival of the plugs at the four
transplanted sites along the York River, including the two different depths
at the Humfort Island locations.
The Guinea Marsh site can be considered as a control for the others
since it consists of a small unvcgetated area surrounded by a very extensive
meadow of Zostera marina that archival photography reveals little changed
since 1937. It is bordered to the north by a string of low marsh islands
dominated by Spartina alterniflora and is located adjacent to the Mobjack Bay
region of the Chesapeake Bay. This area has experienced little decline of
vegetation in recent years. Comparative bionass data are presented in
Section 1 of this report.
The Guinea Mj»rsh site, in contrast to the other transplanted areas, was
characterized by less turbidity (secchi >1.0 m) during most periods. This
appeared due in part to the baffling effect of the surrounding Zostera marina
bed as well as its location in close proximity to the clearer Bay waters.
Qualitatively, water clarity within the bed was particularly good during low
tidal periods when the baffling effect of the grasses had its greatest
impact. The other unvegetated transplant areas appeared much more
susceptible during the suinner months to rosuspension of bottom sediments by
wave action, especially during low tides. This baffling effect of the
vegetation has been similarly observed by Boynton (personal communication) in
Ruppia maritima and Potomageton perfoliatus beds in the upper port ten of the
Chesapeake Bay.
Survival of the Zostera marina plugs was significantly greater at the
Guinea Marsh site than any of the other transplanted areas. Excellent
survival of the plugs was recorded in the unfertilized treatment while a
significant decrease in survival was observed in the fertilized treatment.
1C5
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SUMMER 1979 - Zostera TRANSPLANT
100
6-19 7-12
8-6 8-SI
GUINEA MARSH
50-
-»,^
'10-17 11-7
-• •
Fertilized
Unfertilized
4-2I-8O 6-SO
• •
7-25 8-6
50-
8.5I
ALLENS ISLAND
_J
|
>
o:
r>
V)
.6-19 7-10
.,
0*31
GLOUCESTER POINT
ioori-
50-
0
MUMFORT ISLAND
INSHORE
100-
50-
MUMFORT ISLAND
OFFSHORE
100-
50-
7-l8
I i
PARROT ISLAND
I I
30 60 90 120 150 180 210 240 270 300 330 360
DAYS
Fig. 3. Percent survival of the Summer, 1979, Zostera marina transplants
at the Guinea Marsh, Allen's Island, Gloucester Point, Mumfort
Island and Parrot Island Sites.
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Table 2 presents the perx.-nt survival data for this site on tabular form as
well as data on the mean length of the shoots and the mean number of shoots
per plug for the study period. Initial losses of plugs during June and July
appeared to be the result of uprooting by the physical activity of burrowing
organisms, especially the blue crab. The nuraber of shoots per plug remained
relatively constant during this period, however the mean length of the shoots
rapidly decreased as the tips of the leaves on the longest shoots were broken
off by wave action. Little new growth was evident, including the fertilized
treatment.
Annual late summer senescence characterized the adjacent vegetation in
the SAV bed during months of August and early September and similarly the
transplanted plugs showed little new growth during this period. Although the
mean length of the shoots remained relatively constant the mean number of
shoots per plug and the percent survival decreased, especially in the
fertilized treatment. The difference between survival in the treatments may
have been due more to burrowing by organisms in the fertilized plot rather
than an effect of the fertilizer, since blue crabs were observed in holes dug
under several remaining plu»s, partially dislodging them from the bottom. By
late Spetember the apparently stressful period had passed and there was
little further loss of plugs. In addition some new growth of vegetation was
evident. This compares with a similar period of regrowth observed in the
adjacent Zostera marina bed (Chapter 1).
Due to vandalism and loss of the marking stakes at the original
trasplant site along a section of the river, new 2^. marina plugs were
transplanted at the Aliens Island site in July 1979. Scattered patches of JZ.
marina are found in the vicinity. However, the extensive beds of vegetation,
many hectares in size, which characterized this area prior to 1973 are gone
(Orth, 1976). The summertime turbidity of the water was much higher (0.6-0.8
m, secchi) than that observed for tha Guinea Marsh area. As with the other
upriver cites it appeared that the extensive surrounding unvegetated flats
were susceptible to both wcves and tidal currents with considerable
resuspension of bottom sediments. This resulted in extremely turbid
conditions during many days.
There was a steady loss of the transplants at Aliens Island from July
through September 1979 (Figure 3). "e suspect the poorly developing plants
were simply uprooted during periods of high wave energy. Table 3 illustrates
the almost immediate decreaue in the mean length of the shoots as the longer
leaves were broken off by wave action. During August the number of shoots
per surviving plug as well as the number of surviving plugs rapidly deceased
until by September when there was little left of the original transplants.
It is suggested the shock of transplantation in July, combined with the
stressful summertime conditions of high temperature, heavy epiphyte growth,
and high turbidity precluded the successful establishment of the new
vegetation at this site.
Established small patches of vegetation in the vicinity of Aliens Island
although subject to typical senescence, generally survived the summer. This
suggests that although conditions here were more stressful than at Guinea
Marsh they would not necessarily preclude the survival of an established bed
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TABLE 2.
PERCENT SURVIVAL, MEAN LENGTH AND NUMBER OF SHOOTS PER SURVIVING
PLUG FOR SUMMER, 1979 ZOSTERA MASINA TRANSPLANT EFFORT AT
GUINEA MARSH
Date
6-19-79
"
7-12-79
II
8-6-79
It
8-31-79
"
9-20-79
"
10-17-79
it
11-7-79
ii
Treatment
Fertilized
Unfertilized
Fertilized
Unfertilized
Fertilized
Unfertilized
Fertilized
Unfertilized
Fertilized
Unfertilized
Fertilized
Unfertilized
Fertilized
Unfertilized
No. Plugs
21
21
18
21
17
21
14
20
8
18
8
17
7
17
% Survival
100
100
86
100
81
100
67
95
38
86
38
81
33
81
X Length + s.d.
Shoots"
(cm)
20
20
14
14
10
10
7
9
8
10
9
11
12
12
± 10
± 10
± 6
+ 7
± 3
± 3
± 2
± 2
± 3
± 3
± 2
± 2
± 3
± 4
X Shoots + s.d.
Plugs
10 +
10 +
9 +
12 +
5 +
9 +
4 +
7 +
2 +
5 +
2 +<
5 +
2 +
6 ±
4
4
3
5
2
5
1
3
1
3
0.5
1
1
3
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TABLE 3. PERCENT SURVIVAL, MEAN LENGTH AND NUMBER OF SHOOTS PER SURVIVING
PLUGS FOR SUMMER, 1979 ZOSTERA MARINA TRANSPLANT EFFORT AT
Date
7-23-79
ii
8-6-79
ii
8-31-79
ii
9-18-79
ii
11-17-79
II
ALLEN'S ISLAND
Treatment
Fertilized
Unfertilized
Fertilized
Unfertilized
Fertilized
Unfertilized
Fertilized
Unfertilized
Fertilized
Unfertilized
SITE.
No . Plugs
42
42
42
41
25
29
2
3
0
0
7o Survival
100
100
100
98
60
69
5
7
0
0
X Length+s.d.
Shoots
(en)
21 + 11
21 + 11
10 + 7
8 + /
5 + 2
7 + 2
5 + 2
6 + 3
-
-
X Shoots+s.d
Plugs
8 + 2
8 + 2
5 + 3
8+4
3 + 1
2+2
2+0
3 + 1
-
-
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'••"1
of SAV. Transplantation during a less stressful time of year than the summer
may allow the vegetation to become sufficiently established to survive the
critical August conditions.
Tne Gloucester Point transplant site, in contast to the Guinea Marsh and
Aliens Island areas, currently is completely devoid of vegetation. It, like
all of the other transplanted areas, did contain extensive beds of Zostera
marina prior to 1973. Turbidity throughout the stressful late summer months
appeared similar to the Aliens Island site with secchi disk readings of 0.6
to 0.8 m commonly found.
The transplants showed a steady decline in survival from June with no
transplants surviving by November. As with the Guinea Marsh area there
seemed to be a slight decrease in the survival of the fertilized versus the
unfertilized treatments. The number of shoots per plug rapidly decreased
(Table 4) so that by the end of August the remaining plugs consisted of only
2 or 4 small Zostera marina shoots. Likewise there was a rapid decline in
the mean length of the shoots as the largest and oldest leaves were removed
by wave action with little new vegetative growth to replace them. A small
spurt of growth was observed in September, similar to that obser"-'d at Guinea
Marsh and typical of the growth patterns observed for naturally ^jcurring
vegetation in the region. By November however, all the transpierced plugs
were gone. We believe that the loss of vegetation during the period of
September to November, both a<- this and the Aliens Island site, was not due
to the continued deterioraton of the plants, but rather to one of a series of
storms occurring during this time.
The Mumfort Island site, the most upstream of all the transplanted areas
along the York River, experienced rhe most rapid dieoff of vegetation with no
survival after 50 d.iys (Figure 3). Turbidity always seems highest with
secchi disk readings of 0.6 m or less common during the summer. The
transplanted Zostera marina exhibited no new growth. Within one month, 75
percent of the transplants had died. There was no apparent difference
between the fertilized and unfertilized treatments and at the two depths. By
July the mean lengths of the surviving leaves were greatly reduced in length
(Table 5) as they rapidly turned brown beginning at their tips and ther were
broken off by wave action. The tremendous decline of transplants at this
site appeared a month or more earlier than that of the downriver areas,
suggesting much earlier limiting conditions here.
The Parrot Island transplant site, located along the Rappahannock River,
proved quite similar to the Mumfort Island site on the York River. Although
documented by aerial photography as having extensive bed;* of submerged
vegetation until the early 1970's, the summer 1979, transplants of Z. marina
rapidly declined in abundance. By 50 days after transplantation all the
plugs both fertilized and unfertilized had failed (Table 6).
Fall 1979 Transplanting Effort
Initial survival of the plugs of Zostera marina transplanted during
September and October 1979 was in nearly complete contrast to the results
obtained for those planted during the summer of 1979. The fall transplants
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TABLE 4. PERCENT SURVIVAL, MEAN LENGTH
7-10-79
ii
8-6-79
ii
8-31-79
n
9-18-79
M
11-7-79
it
Treatment
Fertilized
Unfertilized
Fertilized
Unfertilized
Fertilized
Unfertilized
Fertilized
Unfertilized
Fertilized
Unfertilized
Fertilized
Unfertilized
No . Plugs
42
42
34
40
17
28
15
28
2
5
0
0
7o Survival
100
100
81
95
40
67
36
67
5
12
0
0
X Leugth+s.d.
Shoots
(cm)
20 + 10
20 + 10
13+5
14+6
11+4
11+4
5+2
7 + 2
13+4
8 + 2
-
-
X Shoots+s.d
Plugs
10+4
10+4
5+4
10+6
4+3
7+2
3 + 1
2+2
2 + 1
3 + 1
-
-
j- -
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TABLE 5.
Date
6-14-79
"
7-17-79
«
8-6-79
"
6-18-79
ii
7-17-79
»
8-6-79
"
TABLE 6.
Date
6-20-79
6-25-79
7-18-79
7-18-79
PERCENT SURVIVAL, MEAN' LENGTH AND N*U>ffiER OF SHOOTS PER SURVIXIKG
PIL'G FOA SUMN/R, 1979 ZOSTERA MARINA TRANSPLANT EFFORT AT THE
MUMFORT ISLAND
Treatment
Fertilized
Unfertilized
Fertilized
Unfertilized
Fertilized
Unfertilized
Fertilized
Unfertilized
Fertilized
Unfertilized
Fertilized
Unfertilized
SITES .
No. Plugs 7» Survival
42 100
42 100
11 26
9 21
0 0
0 0
42 100
42 100
13 31
23 55
0 0
0 0
X Length+s.d. °. Shoots+s.d.
Shoots Plugs
(cm)
22 + 10 9 + 5
22 + 10 9 + 5
6+3 3 + 2
7+4 4+2
-
.
24 + 14 6 + 3
24 + 14 C + 2
8+4 4+3
7+4 5+2
- -
• * •*. «
PERCENT SURVIVAL, MEAN LENGTH AND NUMBER OF SHOOTS PER SURVIVING
PLUG FOR SUMMER, 1979 ZOSTERA MARINA TRANSPLANT EFFORT AT THC
PARROT ISLAND SITE.
Treatment
Unfertilized
Fertilized
Unfertilized
Fertilized
No. Plugs 1 Survival
84 100
42 100
0 0
0 0
X Length+s.d. X Shoots+s.d.
Shoots Plugs
(era)
18 + 8 10 + 3
20+11 11+4
- _
- _
_
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at all five of the sites exhibited few losses for at least 180 days (Fig. 4).
By the suoner of 1960 however, the decline of vegetation experienced in 1979
was again evident. However, this time only the Parrot Island and Mumfort
Island sites were severely affected. The Parrot Island losses began between
May and June 1960, while the Muafort Island losses began between July and
August 1960, ten months after they were transplanted. The complete loss of
all t^nsplanted oaterial at Parrot Island by August 1980, with very little
before May, suggests that conditions are quite limiting for the survival of
vegetation in that area during these suciaer tsonths. Th» decline of
vegetation at the Mimfort Island site beginning approximately one month later
than Parrot Island suggest that conditions there remain favorable for
surivial somewhat io.i^er into the sucsner. Salinity samples were usually
2 ppt less at Parrot Island than Mumfort Island.
A hypothecs of less stress and increased survival with increasing
proximity to the mouth of the rivers is supported by the increased survival
evident at the Gloucester Point (VIMS) site located downriver from the
Mumfort Island area along the York River. In addition, the nearly
100 percent survival of the transplants at the further downriver Aliens
Islaiid and Guinea March sites indicates that established beds of vegetation
should survive aI these areas. This is in feet what is occurring as the
Aliens Island site approximates the current most upstream limits of naturally
occuring Zostera marina. The aaounts of vegetation are, however, still
greatly reduced from former levels. Recruitment and spreading by seedlings
in the fall and winter nonths froa adiacent Z^. marina beds say be responsible
for many small patches of vegetation found here.
Growth in the transplants as measured by changes in mean area of the
plugs aid mean number of shoots per plug are presented in Table 7. Some
above-ground growth was evident from the September-October transplanting
period through December 1979 at all the sites. The plants appeared quite
healthy with little of the deterioration observed during the summer. There
vas no observable effect of the ammonium nitrate fertilizer on the survival
or growth of the plugs.
Environment*! conditions during this fall period were characterized by
decreasing water temperatures (20*C to 5*C) and reduced turbidity at all
sites. During August 1979, secchi disk readings varied froa approximately
O.i a at the most upstream sites, Mumfort and Parrot Islands, to 1.0 m at
Guinea Marsh. Froa October through December however, it appeared that all
sites had secchi disk readings of 1.0 m or greater.
The period of December 1979 to June 1930 was characterized by tremendous
growth of the fall transplanted vegetation at all of the sites. The Aliens
Island site showed the greatest increase with 17 and 20 fold increases in
mean plug area between December ana Hay for the September 1979 for fertilized
and unfertilized transplants, respectively, and 14 and 15 fold increases in
areas for the October 1979, fertilized and unfertilized transplants.
Increases in the numbers of shoots were 12 and i4 fold and 6 and 11 fold,
respectively. By June 1980, all of the transplants in the various treatments
at this site had grown together so that observations of individual plugs
becase impossible. This period of active growth parallels that observed for
113
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^#3?'l^
FALL 1979 ZOSTERA TRANSPLANT
10-T IZ-« 1-16-60 5 JS 5 9
100-I ° O O ^---g-..-..-^.-
50-
o-
T 22 8-26 IO-Z II-11 80
H^gft^ -=^^" Q
100 -T
GUINEA MARSH
10-2 n-5 12-6 1-16-60 5-2O
50-
7-22 »-?* S-22 H-13-eO
ALLENS ISLAND
SEPT.
• FERTILIZED
UNFERTILIZED
CO
100
50-
0-
100
50-
0-
K-S !2-«
—O O-
-=*:
ALLENS ISLAND
OCT.
GLOUCESTER POINT
50-
0-
-=3.
PARROT ISLAND
3-28-SO 5-2
i i i i i i i i i i i i i i i
0 60 120 180 240 300 360 420
DAYS
Fig. 4. Percent survival of Fall, 1979, Zostera marina transplants.
114
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existing beds of Zostera marina found in this region of the lower Chesapeake
Bay (Chapter 1). The slightly better growth of the September transplants as
compared to the October transplants at the Aliens Island site suggests that
an additional period of growth during the fall is initially beneficial to the
re-establishment of vegetation in this area. However, the steady decline of
all of the transplanted plugs placed at this same location on July 23, 1979
suggests a significant change had occurred between July and September in
environmental factors which had previously been limiting the establishment of
aew vegetation.
A heavy infestation of mud snails (llyanassa obsoletus) was evident from
April tc June 1980, at the Gloucester Point and Mumfort Island sites along
the York River. As described previously, a similar infestation was observed
at Mumfort Island in April 1979. Their presence in extreme numbers may be
d-ie to the lack of vegetation in these areas so that there is little suitable
substiate for laying their eggs. Although the transplanted plugs were
impacted to such a degree that hundreds of the snails completely smothered
the plants for weeks at a time, the vegetation recovered and continued
growing at both sites until August 1980.
From August to September 1980, the characteristic late summer senescence
occurred at all the York River sites. The Guinea Marsh and Aliens Island
areas had become so well established that they were not critically affected
by this period and new growth was evident after September. The Gloucester
Point site showed a considerable decline in the numbers of shoots between
August and September but considerable regrowth was evident by November. The
upriver Mumfort Island site again showed the greatest decline along the Y<*rk
River areas in August with little surviving vegetation by November.
The Parrot Island site, located along the Rappahannock River, showed its
characteristic earlier and more severe decline than any of the York River
areas. Growth was observed throughout the spring until the Juna 20 sampling
but between tuis date and August /, there was a precipitous decline with all
vegetation gone by this latter date. It appears evident, therefore, that
revegetation of this section of the Rappahannock is limited by environmental
conditions present during July.
Spring 1980 Transplanting Effort
Particle size distribution of the sediments within the 0-2, 2-5, 5-10
and '0-15 cm depth segments of the cores are presented in Table 8 for the
four unvegetated York River transplant sites as well as the Guinea Marsh
donor site. The statistical parameters of grain size calculated for these
data are presented in Table 9. These sediment cores were taken on March 14,
1980, several weeks prior to the Spring 1980 transplantation of Zostera
marina at these areas.
Analysis of the particle size distribution indicated that the sediments
within each site were quite homogeneous with respect to depths of at least
15 cm. The graphic mean (f^) and median (Md) measures of average size showed
little change with depth within each core. The inclusive standard deviation
117
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1
1
1
1'
1
w
1
1
1
i
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i
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TABLE 8 . PARTICLE SIZE DISTRIBUTION' (%) FOR DEPTH INTERVALS
CORES AT TRANSPLANT
3-14-80.
Depth
Location Core!? (cm)
Murafort Is. 1 0-2
2-5
11 " 5-10
10-15
Gloucester Pt. 1 0-2
2-5
5-10
10-15
Aliens Is. 1 0-2
ii I. 2-5
" " 5-10
" " 10-15
Guinea Marsh 1 0-2
(unvegetated)
ii » 2-5
5-10
11 " 10-15
Guinea Marsh 1 0-2
(vegetated)
" " 2-5
5-10
10-15
AND DONOR
mm 1.000
0 0
0.22
0.13
0.42
0.23
1.04
0.19
0.44
0.82
0.66
0.18
0.59
0.66
0.55
0.13
0.20
0.39
2.49
0.50
1.01
0.90
SITES
.500
1
5.50
6.70
3.48
3.40
4.24
1.24
1.49
2.1.1
1.53
1.41
1.43
1.68
0.61
0.26
0.46
0.55
1.64
0.87
0.76
0.82
ALONG THE YORK
.250
2
60.20
61.90
57.30
63.50
52.13
53.81
50.03
33.46
27.95
26.50
28.82
35.63
13.49
3.25
3.45
7.52
9.22
14.87
12.30
8.12
.125
3
25.50
21.20
27.10
22.20
29.71
34.76
37.20
32.76
54.60
54.78
54.26
46.78
64.86
78.19
75.28
75.94
56.70
59.04
63.85
70.03
OF SEDIMENT
RIVER,
.063
4
1.23
1.25
1.68
1.62
1.92
2.03
1.88
2.08
5.73
9.02
5.80
7.64
9.58
7.%
9.87
',.12
14.64
10.57
9.00
8.88
<.063
5
6.98
7.91
9.11
8.76
10.14
7.51
6.98
7.95
9.08
8.86
8.49
8.69
10.14
7.51
6.98
7.95
13.63
12.86
11.18
10.71
118
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1
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.
-- "-;.-• ,.- •
.••' , --••;,••;-•!>•- w ..,.--," >o
TABLE 9 . STATISTICAL PARAMETERS OF GRAIN SIZE FOR DEPTH INTERVALS OF
SEDIMENT CORES AT TRANSPLANT AND DONOR SITES ALONG THE YORK
R^VER, 3-14-80.
Depth
Location Co"e # (en)
Mumfort Is. I 0-2
it 2-5
" 5-10
10-15
Gloucester Pt. 1 0-2
" " 2-5
" " 5-10
" " 10-15
Aliens Is. 1 0-2
" .1 2-5
" " 5-10
" " 10-15
Guinea Marsh 1 0-2
(unvegetated)
ii i. 2-5
" " 5-10
11 " 10-15
Guinea Marsh 1 0-2
(vegetated)
ii it 2-5
" " 5-10
" " 10-15
Mean
(M )
1.9
1.9
2.0
2.0
2.0
2.1
2.1
2.0
2.3
2.4
2.3
2.3
2.7
2.7
2.8
2.6
2.4
2.8
2.8
2.7
i •? sv
Median
(Md)
1.8
1.7
1.8
1.8
1.9
2.0
2.0
1.9
2.3
2.4
2.3
2.2
2.6
2.6
2.6
2.6
2.6
2.6
2.6
2.6
Sorting
(01)
0.81
0.86
0.81
0.79
0.85
0.74
0.77
0.80
0.77
0.80
0.77
0.78
0.75
0.55
0.61
0.58
0.94
0.88
0.84
0.70
Skevmess
(SK})
+0.33
+0.42
+0.43
+0.46
+0.35
+0.45
+0.34
+0.37
+0.15
+0.14
+0.15
+0.22
+0.21
+0.34
+0.34
+0.18
+0.18
+0.28
+0.28
+0.25
I
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or sorting coefficient (0"I) indicated that the sediments were moderately
sorted (Folk, 1968) at all depths at all sites. The inclusive graphic
skewpess measure (SK^) revealed the sediments to b<= fine-skewed to strongly
fine-skewed with little effect of depth. This homogeneity of the sediments
within each core were similar to the results obtained at a Zostera narina and
Ruppia maritima bed located nearby at Brown's Bay and presented in Section 5
of this report.
Between-site variation was significantly greater than within site
variation with depth. The most upriver Mumfort Island site had ths largest
(smallest phi) median and mean measures of average size (Table 9).
Proceeding downriver, each transplant site had an incremental reduction in
the average size of the sediment particles with the finest sediments found at
the Guinea Marsh area located at the mouth of the river. Analysis of the
particle size distribution information (Table 3) reveals a shift from 1 and 2
phi particles at Mumfort Island to 3 and 4 phi at Guinea Marsh site with
intermediate values at Gloucester Point and Aliens Island areas. This
graJation in size may be representative •( large scale sorting of littoral
sediraents from upriver to downriver or simply may be an artifact of more
localized physical sedimentation processes such as distance from an adjacent
sediment source. Within the Guinea Marsh area the vegetated core had the
largest percentages of fine material (4 and 5 phi particles) as might be
expected. Although there were differences in particle sizes between
transplant sites these slight differences are certainly withii. the range of
sediments where Zostera marina is found locally and would not preclude the
rrestablishment of veg?tation. The relatively small difference between the
unvegetated, denuded areas and the vegetated bed as well as data from earlier
studies in the region (Orth, 1973) suggests that there has been little
appreciable change in the sediment type along the York River since the
disappearance of the Z. marina beds.
Extractable sediment pore water and surface water nutrient
concentrations for replicate cores taken at the Guinea Marsh, Aliens Island,
Gloucester Point and Mumfort Island transplant sites on March 14, 1980 are
presented in Tables 10,11, 12 and 13, respectively. Similar data were
obtained for cores taken in a Zostera marina and Ruppia maritima bed at
Brown's Ray and are presented in Section 5 of this report.
Ammonium levels in the sediments at each of the transplant sites show
little significant variation between sites. There were few obvious patterns
of change with depth, however several of the cores exhibited lowest
concentrations at depths less than 2 cm. This may be the result of the
diffusion of mineralized ammonium from the sediment into the water column or
aerobic nitrification. Higher ammonium levels in the 0-2 eta layer of the
vegetated versus unvegetated Guinea Marsh cores is similar to that observed
in the vegetated and unvegetated cores at Brown's Bay (Section 5). This may
be due to the greater perturbation of th° sediments within the unvegetated
area resulting in increased diffusion or denitrification of ammonium when
compared to the more protected vegetated zone or less detrital input.
Nitrate levels in the .-sediments were extremely low at the Kumfort Island
and Gloucester Point trcnsplant sites suggesting rapid uptake or
120
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1
1
1.
1
1
t
1
f
1
1
1
1
1
•V
1
W
1
I
1
»-"••'>—- • —
TABLE 10. SEDIMENT PORE
i
j
WATER NUTRIENT CONCENTRATIONS
MARSH TRANSPLANT AND
Core Depth
Vegetated-1 water
0-2
11 2-5
" 5-10
" 10-15
Vegetated-2 water
11 0-2
11 2-5
5-10
" 10-15
Unvegetated-1 water
" 0-2
" 2-5
" 5-10
" 10-15
Unvegetated-2 water
" 0-2
" 2-5
11 5-10
" 10-15
NH*
0.8
92.1
78.8
56.0
37.4
0.6
J07
209
44.8
50.4
0.4
25.6
96.7
170
206
0.4
10.9
46.9
79.1
97.9
DONOR SITES,
N0~
1.0
6.91
8.16
0.91
0.28
0.4
3.03
2.04
0.57
0.57
0.6
1.43
0.88
2.94
0.32
0.5
1.03
1.11
0.45
1.19
3-14-80.
»o;
0.1
1.53
1.30
2.24
0.91
0.2
3.52
3.86
1.36
0.99
0.1
2.27
2.95
1.50
0.96
0.96
1.64
1.50
1.11
1.08
..-••/•
(pM) AT GUINEA
P°4~3
0.4
7.84
21.6
16 1
8.11
0.6
18.0
50.2
12.4
8.40
0.3
8.85
27.2
17.2
11.6
0.3
8.15
16.8
13.8
11.5
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TABLE 11. SEDIMENT PORE WATER NUTRIENT CONCENTRATIONS (pM) AT ALIENS
ISLAND TRANSPLANT SITE, 3-14-80.
Core
Unvegetated 1
it
ii
ii
ii
Utivegetated 2
ii
it
ii
ii
Depth
water
0-2
2-5
5-10
10-15
water
0-2
2-5
5-10
10-15
NH*
0.6
55.1
172
90.7
119
0.4
82.9
25.0
78.0
92.0
N0~
0.1
<0.01
<0.01
2.82
0.81
0.2
<0.01
0.27
0.05
7.79
N0~
0.1
9.04
6.55
11.4
1.56
0.1
1.08
0.68
0.62
2.38
*°4-3
0.3
9.76
46.8
79.6
38.6
0.4
11.48
4.66
7.62
8.43
122
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TABLE 12. SEDIMENT.PORE WATER NUTRIENT CONCENTRATIONS (pM) AT GLOUCESTER
POI:;T TRANSPLANT SITE, 3-14-80.
Core Depth NH* N0~ N02 P04~3
Unvegetated 1 water 0.56 1.05 0.14 0.36
" 0-2 20.0 <0.01 1.68 7.07
2-5 28.3 <0.01 1.98 i5.0
" 5-1^ 7.28 <0.01 0.47 10.1
" 10-15 103 <0.01 0.58 14.3
Unvegetated 2 water 0.48 0.72 0.14 0.37
! " 0-2 9.33 <0.0i 0.47 3.14
" 2-5 45.9 <0.01 1.76 17.8
1
" 5-10 103 <0.01 5.31 25.3
" 10-15 162 <0.01 6.63 31.3
123
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TABLE 13. SEDIMENT PORE WATER NUTRIENT CONCENTRATIONS (pM) AT MUMFORT
ISLAND TRA:;SPLANT SITE, 3-iA-so.
Core
Unvegetated 1
it
ii
ti
ii
Unvegetated 2
ii
ii
ii
it
Depth
water
0-2
2-5
5-10
10-15
water
0-2
2-5
5-10
10-15
NHj
0.07
16.4
73.1
116
86.2
0.83
12.7
43.3
78.6
73.1
NO'
3.95
<0.01
<0.01
<0.01
<0.01
3.72
<0.01
<0.01
<0.01
<0.01
N0~
0.16
0.30
0.36
0.50
0.33
0.15
0.50
2.06
0.85
0.52
V1
0.27
0.97
3.61
4.86
2.43
0.25
2.99
18.2
17.8
15.1
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^
denitrification by bacteria of any available nitrate with little
accumulation. The Aliens Island site showed somewhat higher levels in the
sediments. Interestingly the highest levels were recorded in the Guinea Marsh
vegetated cores at depths less than 5 cm.
Nitrite levels were consistently higher than nitrate levels in the
sediments at all sites except for the Guinea marsh area. Conversely nitrite
levels in the water were consistently lower than nitrate.
Inorganic phosphate levels varied considerably but were generally
comparable at the vegetated donor site and the unvegetated transplant areas.
Similar values were obtained for vegetated and unvegetated areas in the
Brown's Bay region (Chapter 5). Within each unvegetated core lowest levels
of phosphate generally occurred in the top 0-2 cm of sediment.
Table 14 presents the results for the extractable sediment pore water
and surface water nutrient concentrations for the unfertilized, vegetated
Zostera marina transplants at the Aliens IsLand site at 10 days (4-17-80) ar.d
37 days (5-14-80) after transplantation. Table 15 presents results of
similar data for the existing unvegetated &nd unfertilized sediments at the
site. In general there appears little difference between the vegetated and
unvegetated cores at each of the dates. Phosphate levels are higher in the
vegetated, May 14, samples as compared to the unvegetated cores however
extractable phosphate levels varied considerably.
Both treatments show similar patterns! for several of the nutrient
species. Nitrate levels were considerably higher in both the vegetated and
unvegetated cores during the April 17, sampling than on May 14. All other
nutrient levels were comparable during both dates. Ammonium and inorganic
phosphate levels were generally lowest in the 0-2 cm sections of the cores on
both dates in both treatments. Possibly uptake, conversion or loss of thes*-
two species into the water column through diffusion is occurring. Regardless
of their fate there was little significant effect of the vegetation evident
on the extractable nutrient concentration in the sediments.
Levels of extractable nutrients in the unvegetated sediments 10 and 37
days after treatments with Osmocote or ammonium nitrate fertilizers are
presented in Tables 16 and 17, r«>sf°ctively. Depths of fertilizer placement
varied between 10 to 15 cm below the surface. Both fertilisers showed
tremendous increases in all the nitrogen species. Due to the anaerobic
conditions, and the types of fertilizer used, the largest fraction of
nitrogen was present as ammonium, a species that is chemically st'.ule under
reducing conditions. Highest concentrations of ammonium were found at depths
of 10 to 15 cm with a gradient of concentrator to tho sediment surface in
these unvegetated areas. High levels of ammonium in the overlying water 10
days after application indicates initial significant losses by diffusion into
the water column. Continued high levels of ammonium were found in the
sediments 37 days after transplantation in both treatments. The Osmocote
treatment, due to the slow release nature of the fertilizer, would be
expected to continue these higher levels of ammonium for a considerably
longer period than aumonium nitrate.
125
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TABLE 14. SEDIMENT PORE WATER NUTRIENT CONCENTRATIONS (pM) AT A1LENS ISLAND
TRANSPLANT SITE, VEGETATED AND UNFERTILIZED »LUCS.
Date Core
4-17-80 £1
it it
ii ii
it M
ti it
A- 17-80 *2
t: it
ii ti
it ii
ii it
5-14-80 #1
it ii
it ii
if tt
it »
5-14-80 *2
it ti
it ii
it ii
ti ii
Depth
(cm?
water
0-2
2-5
5-10
10-15
water
0-2
2-5
5-10
10-15
water
0-2
2-5
5-10
10-15
water
0-2
2-5
5-10
10-15
NH*
0.20
20.5
64.0
125
154
0.01
35.0
121
181
87.2
0.20
12.8
83.9
117.7
3.13
0.09
8.63
80.5
245
149
N0~
<0.01
16.4
24.0
82.9
66.6
<0.01
6.66
.52
5.04
24.3
0.35
0.87
1.3i
0.60
0.62
0.12
0.28
0.31
<0.01
0.09
Is'O^
2.13
3.84
6.71
3.66
2.01
2.04
0.44
1.40
0.61
1.05
0.11
0.78
0.87
0.96
0.61
0.10
0.78
0.96
2.7*
0.78
V3
2.65
7.87
18.5
19.0
19.1
3.50
0.76
13.2
14.8
4.00
0.29
l*.'.~t
23.2
46.3
3.72
0.28
2.80
29.0
43.6
3.98
L
126
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TABLE 15. SEDIMENT PORE WATER NUTRIENT CONCENTRATIONS (>iM) AT ALLENS
ISLAND TRANSPLANT SITE, UNVECETATED AND UNFERTILIZED PLUGS.
Date Core ^fP^V
4-17-80 11 water
0-2
2-5
5-10
10-15
4-17-80 12 water
" 0-2
it it *t e
*. j
" " 5-10
10-15
5-14-80 #1 water
" " 0-2
« « 2_5
5-10
10-15
5-14-80 (2 water
» " 0-2
" " 2-5
" " 5-10
" " 10-15
SH+
<0.01
14.6
150
52.2
126
<0.01
S.68
233
201
144
o.o:
6.36
30.4
89.1
101
<0.01
12.4
128
166
97.8
3
<0.01
6.07
49.1
3.31
37.2
<0.01
9.85
185
52.6
6.86
0.06
0.66
0.06
<0.01
0.30
0.02
0.13
0.20
1.72
0.12
NO;
2.13
0.35
0.70
0.96
4.10
2.30
2.01
9.68
9.94
1.05
0.10
0.61
0.78
0.61
0.61
0.08
0.61
0.61
0.52
0.52
P04-3
2.89
0.99
2.18
11.0
10. b
2.84
4.27
18.7
39.2
15.2
0.24
0.60
3.86
9.62
5.44
0.19
1.13
11.1
13.3
7.18
127
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TABLE 16. SEDIMENT PORE WATER NUTRIENT CONCENTRATIONS (pM) AT ALLENS
ISLAND TRANSPLANT SITE, UNVEGETATED PLUGS FERTILIZED WITH
OSMOCOTE.
- -=========
Date
4-24-80
II
11
11
II
4-24-80
it
it
ii
n
5-21-80
n
n
it
ii
5-21-80
ti
ii
11
ii
— —
Core Depth
(cm)
#1 water
» 0-2
n 2-5
5-10
» 10-15
#2 water
» 0-2
2-5
i. 5-10
« 10-15
tl water
» 0-2
n 2-5
M 5-10
10-15
82 water
•• 0-2
2-5
n 5-10
" 10-15
—
NK3
12.0
13400
30500
23000
23100
41.2
13600
38200
41700
78100
1.31
4540
10700
55000
21000
2.16
3650
5130
18700
27400
—
N0~
7.77
1540
6570
6840
7790
24.9
4520
16400
21700
51000
0.03
450
131
861
1120
0.67
12?
400
7690
14800
_ _ — •
NOj
0.23
708
1550
1620
130
5.01
120
488
4290
444
0.06
<0.01
<0.0l
32.4
410
0.34
3.82
112
11.9
305
_V
0.20
11.0
162
314
352
0.49
6.77
142
315
534
0.16
1040
1020
819
510
0.22
13.0
252
1830
2090
128
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1
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1
1
1
1
1
1
1 1
;
i !
*
i
•• ~r
i
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••
1
1
«,
X
• - , - ,JV
:
TABLE 17. SEDIMENT PORE WATER NUTRIENT CONCENTRATIONS (pM) AT ALLENS
ISLAND TRANSPLANT SITE, UNVEGETATED PLUGS FERTILIZED WITH
AMMONIUM NITRATE.
Date Core Depth
(cm)
4-24-80 01 water
I. •• 0-2
ii H 2-5
" " 5-10
" " 10-15
4-24-80 j?2 water
» » 0-2
ii •• 2-5
11 " 5-10
11 10-15
5-21-80 n water
ii ii o-2
ii •• 2-5
" " 5-10
" " 10-15
5-21-80 #2 water
ii " o-2
ii •• 2-5
" " 5-10
11 " 10-15
-
NH*
0.88
5680
15600
24600
37700
17.2
12600
18800
24800
35600
0.12
4130
6870
14700
21100
0.53
5780
6310
10400
11300
129
N03
0.07
683
9450
14600
15000
11.6
3220
6710
14000
24800
<0.01
131
3.77
438
4420
0.16
578
291
872
1530
N0~
0.13
0.24
9.29
2220
8160
5.04
1420
2150
2620
3950
0.06
<0.01
<0.01
74.4
1700
<0.01
8.01
3.51
4.21
2.48
V
0.21
2.99
25.4
26.6
5.97
0.20
2.12
2.07
2.05
3.19
1.18
35.7
72.4
61.6
18.3
1.87
4.31
35.8
32.1
7.25
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Levels of nitrate and liiirite in the interstitial vere also raised
considerably by the additions of the fertilizers to the unvegetated
sediments. Hignest levels were again fo'jnd at depths between 10 and 15 cm
with lowest levels in the upper two centimeters near the sediment surface.
High levels in the overlying water indicate considerable diffusion into the
water column was occurring 10 days after transplantation. Reduced levels of
nitrate ant! nitrite in the sediments found 37 days after application indicate
much of these two inorganic nitrogen spucies had been lost. Most likely
uptake, diffusion and denitrification are responsible for these reductions.
Highest levels were evident during this period at depths b»low 10 cm
suggesting some continued input of these two oxidized forms of nitrogen from
the fertilizers.
Levels of phosphate in the sediments differed between the two fertilized
treatments. Since no phosphate was present in the ammonium nitrate
fertilizer, levels of inorganic phosphorous were comparable to the
unfertilized treatments during these dates. Osmocote on the other hand which
was 14 percent phosphate, raised the levels in the sediments considerably,
although not nearly as high as for the nitrate and ammonium component. This
suggests that much of the phosphorus supplied by the fertilizer was being
precipitated with ferric iron or other heavy metals and bound in the
sediments.
Tables 18 and 19 present the results of the sediment and water nutrient
concentrations for the vegetated plugs fertilized with Osmocote find ammonium
nitrate, respectively. On April 17, ten days after transplantation levels of
ammonium in both of the osaocote treatment cores and one of the
ammonium-nitrate cores were considerably less than that observed in the
unvegetated treatments, suggesting uptake of ammonium by the plants was
occurring. After 37 days levels of ammonium in the osmocote transplants
increased slightly while those in the emaonium nitrate treatment showed
varied results. Concentrations in the sediments were highest in both
treatments at the 10-15 cm depths with reduced levels towards the surface.
Levels of nitrate and nitrite in the sediments generally showed
considerable declines from 10 to 37 days after application in a similar
manner to that experienced by the fertilized, unvegetated plugs. High levels
of nitrate and nitrite in the surface water at 10 days after application
indicates a considerable amount of leaching was initially important. Other
reductions in the levels may have been due to denitrification, uptake by the
plants and sediment microorganisms.
Phosphate levels showei significant increases over the nonfertilized
treatments at 10 and 37 days after application for only the osaocote
fertilized plugs. This is similar to the results observed for the
unvegetated plugs. Reduced levels of phosphate were observed in several of
the cores in the 0-2 cm depth interval in vegetated as well as the
unvegetated cores. This suggests either diffusion into the surface watar or
precipitation of upward diffusing phosphate in an insoluble form at this
aerobic layer.
130
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•
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1
1
Wi
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i
i^B
1
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1
1
1
-
^-^ ] ' ;
TABLE 18. SEDIMENT PORE WATER
NUl'RIENT
CONCENTRATIONS ()jM)
ISLAND TRANSPLANT SITE, VEGETATED PLUGS
Date Core Depth
(cm)
4-17-80 #1 water
" " 0-2
" " 2-5
5-10
" " 10-15
4-17-80 12 water
" " 0-2
ii i, 2-5
5-10
" 10-15
5-14-80 SI water
" •• 0-2
.. .. 2-5
" " 5-10
10-15
5-14-80 #2 water
» 0-2
ii i. 2-5
" " 5-10
" " 10-15
NH*
17.8
404
799
994
999
3.63
630
986
997
999
0.74
7040
5700
11100
21500
0.27
2480
2190
1910
4470
N°3
3210
47.5
158
9170
19400
42.4
53.3
5 J.I
286
63-00
<0.01
6240
54.8
<0.01
3650
<0.01
<0.01
<0.01
<0.01
547
AT ALLEN S
FERTILIZED WITH OSMOCOTE.
2
3.15
0.94
1.70
12.8
8.42
<0.01
37.8
62.3
165
68.6
0.25
2.21
2.80
297
516
0.07
0.86
1.45
1.45
4.15
•V3
3.63
35.7
9.45
241
4.65
41.5
302.3
511
599
0.28
2.85
107
412
414
0.48
4.23
8.22
6.41
67.8
131
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TABLE 19. SEDIMENT PORE WATER NUTRIENT CONCENTRATIONS (pM) AT ALIENS
ISLAND TRANSPLANT SITE, VEGETATED PLbJS FERTILIZED WITH
AMMONIUM NITRATE.
Date
A- 17-80
ii
it
ii
ii
A- 17-80
It
IB
|l
II
5-14-80
ii
ii
it
ii
5- 14-80
it
ii
it
M
Core Depth
(cm)
#1 water
" 0-2
11 2-5
" 5-10
10-15
#2 water
0-2
2-5
" 5-10
11 10-15
ifl water
11 0-_
11 2-5
5-10
11 10-15
$2 water
11 0-2
2-5
11 5-10
" 10-15
NH*
2.76
801
995
996
995
22.1
937
40100
124000
9400
0.25
4330
5600
7390
6160
0.22
3150
4530
67AO
7180
N0~
20.3
598
46100
4660
46100
847
3050
21000
132000
139000
0.01
322
386
449
614
0.03
195
322
323
321
N0~
7.97
1.28
1.79
2.89
1./9
491
4.42
515
644
386
0.05
<0.01
<0.01
<0.01
24.9
0.06
<0.0l
<0.01
<0.01
0.59
P04~3
3.11
38.6
73.0
b9.9
73.0
2.79
11.1
28.7
98.2
34.6
-
2.67
2.67
4.24
5.44
0.20
2.96
5.40
2.32
0.01
132
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Percent survival of the Zostera marina plugs transplanted in April 1980,
at the four York. River transplant sites are presented in Figure 5. Few
losses were observed at any of the sites until June, 19, after which time the
Mumfort Island site began a precipitous decline. Loss of plugs during the
su inner months at this location parallels the results of every other
transplant effort at this site regardless of ..-hen initiated. Gloucester
Point and Aliens Island locations demonstrated intermediate levels of
survival with Osmocote fertilized plugs at the Aliens Island site having the
greatest success. The Guinea Harsh control site in contast to other areas
showed no loss of plugs up to the end of the study period in November 1980.
Growth or decline of the plugs as evidenced by mean area of the plugs
and mean number of shoots per plug is presented in Table 20. Figure 6
presents graphically the mean number of shoots per plug data. Guinea Marsh
transplants demonstrated over a three-fo1--1 increase in number of shoots per
plug and a fifteen-fold increase in area from April to July. Summertime
senescence was evident from July through September while an increase in both
area and number of shoots was evident from October to November.
An effect of fertilizers on growth was evident at the Aliens Island
treatments. All three treatments showed increases in the number of shoots
per plug from April to July with growth of the Osmocote fertilizer continuing
until August. The greatest response was evident in the Osmocote treatment
followed by the a-amonium nitrate fertilizer. Although the sediment nutrient
analyses showed extremely high levels of ammonia after 37 days for both
fertilizers, continued high levels would be expecr.ed from Osmocote because of
its slow release nature. In addition, although inorganic phosphorus has not
been regarded as limiting to growth of submerged grasses, high levels found
in the sediments after application of Osmocote indicate that it cannot be
ruled out as & contributing factor to the growth in this case. Senescence
was evident in all three treatmenti in late summer from August to September
while an additional characteristic spurt of growth was observed from
September to November.
Application of Osmocote resulted in a 325 percent increase in the mean
number of shoots per plug over the unfertilized treatment and a 220 percent
increase in mean area. The ammonium nitrate on the other hand showed only a
40 percent increase in the number of shoots and a 71 percent increase in
area. Churchill et al., 1978, found little positive effect of Osmocote on
Che growth or survival of his miniplvgs transplanted in Long Island. His
application .rates, (3.5 g vs 40 g here), as well as his application
techniques, suggest there was limited availability of the fertilizer for
uptake by the plants.
The Gloucester Point transplant site was heavily impacted by mud snails
during April and May 1980. Effect of the snails on the growth of the plugs
is evidenced by a comparison of the caged and uncaged treatments (Fig. 5 and
Table 20). Tlie total number of surviving plugs, mean area of the plugs and
the mean number of shoots per plug were significantly greater in the caged
versus the uncaged treatment on June 16, 1980. At this time the snails had
completed their egg laying and were for the most part, gone from the Zostera
marina plants. The cages were therefore removed. By July 22, 1980 the
133
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11 . . '
1
1
H 100-
• ~ 50-
1
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i
150-
|
t cc
!
, *- too-
1
r so-
1 J
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I
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0-
1
1 Fig. 5. Percer
1
1
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\ , '.
SPRING 1980 - Zostera TRANSPLANT
5-9 7-22 8-26 10-2 n'_t'3
GUINEA MARSH
5 , - |C /OSMO. PERT
r »«=^- « ?-2<* 8'26 9"22 / H-13
* :— *— — _^1- • ~*
* . • — -^.
'"'-•-. ^UNFERT
NM4N05 FERT^^ ' ..
ALLENS ISLAND *
1 ^^^
^*-^-~__9-22 11-13
GLOUCESTER POINT
5-9 6-19
X,
-25
3O 60 90 120 150 180 210
MAY JUN JUL AUG SEP OCT NOV
it survival cf Spring, 1980, Zostera marina transplants.
134
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SPRING 1980- Zoslera TRANSPLANT
A.I OSMO PERT.
MAY
Fig. 6. Mean number of shoots vs. time for Spring, 1980, Zostera marina
transplants.
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previously caged 2^. marina plugs had expanded an average of 14 percent in
area but had increased nearly 75 percent in numbers of shoots per plug. The
uncaged plugs on the other hand decreased an average of twelve percent in
area and 23 percent in numbers of shoots during this same period.
From July to August both sets of Spring 1980, transplants at the
Gloucester Point site underwent their typical summer dieback as water
temperatures averaged nearly 30°C and light attenuation reached near maximum
levels (Fig. 5). The mean areas of the plugs increase^ as the individual
shoots spread apart, due in large part to the separation of the rhizome
networks, while the mean number of shoots per plug decreased slightly. The
average caged plug still had five times the number of shoots as compared to
the uncaged transplants. By September 22, both sets of transplants had
decreased nearly 50 percent in numbers of shoots from their August levels.
However, water temperatures after this time dropped below 20*C and light
attenuation decreased dramatically so that by November 13, 1980 new growth
was evident in both the caged and uncaged treatments. At this time the
average plug from which the mud snails hid been excluded in the spring, had
three times the number of shoots of its snail impacted counterpart.
In contrcst to the three downriver stations the Munfort Island site was
the only location none of the vegetation survived tha summer. These results
are similar to that of the spring 1979, transplants placed here. As with the
Gloucester Point site mud snail infestations became severe in April but
continued for a slightly longer period until late June. There were no plugs
protected from the snails by the cages at Mumfort Island. By July 10, 1980
the snails had left the vegetation and observations indicatd a loss of
approximately one third of the plugs, a nearly six fold spreading in the mean
areas of the plugs with an approximately two fold increase in the number of
shoots per plug. Thus some growth had continued despite the apparently
severe impact of the snails. After July 10 however, a precipitous decline
ensued, such that by Augusc 26, all the remaining vegetation had died.
Patterns of growth and decline of the fall Zostera marina transplants
closely follow that of water temperaturs. At temperatures below 25°C
survival of the plugs is excellent with growth occurring primarily when
temperatures are betwen 10°C and 20°C (Fig. 7). These patterns of growth are
very similar to those observed by Setchell (1929) in his early studies of Z_.
marina. Transplantation jf Z. marina at most sites during the summer when
water temperatures are above 25°C resulted in a significant decline of the
vegetation at most sites. Transplantation during September and October when
temperatures were 25*C or less resulted in little mortality until the
following summer. Transplantation during the spring resulted in growth until
temperatures again approached 25 °C. A compounding factor to this observation
of temperature stress is the fact that not all of the sites responded
similarly to the high temperatures. Although there was no observable
difference between the temperatures at each of the sites, the summertime
declines occurred earlier and were more severe the further upriver the
transplants were made. This suggests another factor or factors that may be
acting synergistically with temperature controlling the survival of the
plants.
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Salinity is a parameter that generally decreases with distance upriver
in estuarine systems such as the Chesapeake Bay and its tributaries.
However, salinities were generally quite comparable at each of the York River
sites and only slightly less at the Parrott Island location. In addition,
although low salinities can limit the survival of Zostera mariua plants the
periods of summertime decline observed here were generally characterized by
increasing salinity at all sites.
Biological impacts from organisms such as Illyanassg obi.oletus, the mrd
snail, were most severe in the upstream York River areas of Gloucester Poxnt
and Mumfort Island. Exclusion of the snails by the use of cages a: the
Gloucaster Point location significantly in .'eased the growth and survival of
the plugs here. The snails ar« definitely a stress to the transplants,
however, in most cases the decline of the vegetation occurred sometime after
the snails had left the vegetation. In addition, the Parrot Island site
which had the most severe and rapid loss of vegetaation of any of the areas
had no significant infestation of snails. This suggests that although the
mud snails can decrease the growth and survival of transplanted vegetation
they are not solely responsible for the summertire losses at the upriver
sites.
Daily mean attenuation coefficients taken from June to November 1980, at
the Guinea Marsh, Aliens Island, Gloucester Point and Mumfort Island
transplant site ar
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site.
142
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Fig. 11. Mean daily attenuation coefficients (Kd) for Mumfort Island
transplant site.
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large amounts of sediment but the resultant intact root structure
provides i excellent anchor in the typically high energy transplant
sites.
Transplantation of Zostera niarina by the use of plugs of wild plants in
the lower Chesapeake Bay is a viable management option for mitigation in
regions that currently have existing vegetation. Transplantation is
feasible in these areas during the summer, fall and early spring periods,
but greatest survival has been demonstrated in the fall, followed by the
spring, with least survival of those transplanted during the summer.
Transplant of Zostera marina into regions currently denuded of vegetation
can be attempted during the fall, although survival through the following
summer may be minimal. ;
Location of a transplant site is critically important to the survival of
the vegetation. In most cases areas to be transplanted must have
previously supported Zostera marina beds and have depths between 0.5 and \
1.0 m at MLW. Survival of transplanted areas is inversely related to the
distance upriver from ?.reas of existing vegetation, with the poorest
chances for success in those areas where Z_. marina historically has
experienced its most upriver limits.
The use of ammonium nitrate fertilizer (37-0-0) implanted at 10 to 15 cm j
depths in the sediment under the transplanted plugs had no significant j
effect on the growth of plugs transplanted during the summer and fall i
periods. It did increase the growth of transplants in one area where '
established vegetation was present during the spring of 1980. Its use is :
not recommended. Osmocote fet'lizers (14-14-14) used in a similar manner }
at the same location and time resulted in significantly greater growth of j
the Zostera marina. Its use is recommended. >
s
Monitoring the growth and survival of the Zostera marina transplants |
during this study has revealed that dieback begins in the farthest i
upstream sites when temperatures reach 20°C by approximately June 1. ',
Declines begin lat'r in the downriver areas as temperature reaches 25 °C.
The stressful period ends as temperatures drop to between 20*C and 25*C I
during September. The longer the period of time that the Zostera marina •
can be transplanted before these high temperatures are reached, the '
greater the success rate.
The greater average light extinction observed in the upriver areas along
with poorest survival rates at these sites duiing the summer suggest that
reductions in available light may be acting synergistically with high
temperatures to limit the growth of the transplanted vegetation and to
control natural regrowth. Abnormally high reductions in available light,
combined with high summertime water temperatures may have been
responsible for the recent rapid loss of natural vegetation from many of
these now denuded areas.
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REFERENCES
A.^dy, C. E. 1947a. Eelgras* planting guide. Maryland Consrvationist
24:16-17.
Addy, C. E. 1947b. Germination of eelgrass seed. J. Wildl. Manag. 11:279.
Churchill, A. C., A. E. Cok and M. I. Riner. 1978. Stabilization of
subtidal sediments by the transplantation of the seagrass Zostera marina
L. New York Sea Grant Publ. 78-15. 48 pp.
Duncan, F. M. 1933. Disappearance of Zostera marina. Nature 132:483.
Eleuterius, L. N. 1975. Submergent vegetation for bottom stabilization.
Pp. 439-456 jji Estuarine Research 2:439-456.
Folk, R. L. 1961. Petrology of sedimentary rocks. Hemphill's, Austin,
Texas. 170 pp.
Fonseca, M. S., . J. Kenworthy, J. Homziak and G. W. Thayer. 1979.
Transplanting of eelgrass and shoalgrass as a potential of economically
mitigating a recent loss of habitat. Proceedings of the Sixth Annual
Conference on Wetlands Restoration and Creation, May 19, 1979. Dorothea
P. Cole, Editor. Hillsborough Community College, Environmental Studies
Center, and Tampa Port Authority, Tampa, Florida, pp. 279-326.
Ginsburg, K. N. and Lovmestata, H. A. 1958. The influence of narine bottom
communities on the depositional environmental sediments. J. Geol.
66:210-318.
Gravitz, N. and L. Gleye. 1975. A photochemical side reaction that
interferes with the phenolhypochlorite assay for ammonia. Limnol.
Oceanogr. 20:1015-1017.
Kelly, J. A., Jr., C. M. Fuss and J. R. Hall. 1971. The transplanting and
survival of turtlegrass, Thalassis testudinum, in Boca Ciega Bay,
Florida. Fish Bull. 69:273-280.
Koroleff, F. 1970. Direct determination of ammonia in natural waters as
indophencl blue. Pp. 19-22 in Information of techniques and methods for
seawater analysis. ICES, Service Hydroraphique.
Liddicoat, M. I., S. Tibbitts and E. I. Butler. 1975. The determination of
araaonia in seawater. Limnol. Oceanogr. 20:131-132.
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Maggi, P. 1973. Leprobleme de la disparitura des herbiers a Posidonies dans
le Golfe de Grans (Var). Science et Peche 221:7-20.
Marsh, G. A. 1970. A seasonal study of Zostera epibiota in the York River,
Virginia. Ph.D. Thesis, College of William and Mary, Williansburg,
Virginia. 155 pp.
Marsh, G. A. 1973. The Zostera epifauna of eelgrass in a Virginia estuary.
Chesapeake Sci. 14:87-97.
Marsh, G. A. 1976. Ecology of the gastropod epifauna of eelgrass in a
Virginia estuary. Chesapeake Sci. 17:182-187,
McRoy, C. P. and C. Helffeirch. 1977. Seagrass ecosystems: a scientific
perspective. Marcel Dekker, Inc., New York. 314 pp.
Milne, L. J. and M. J. Milne. 1951. The eelgrass catastrophe. Sci.
American 184:52-55.
Odura, H. T. 1963. Productivity measurements in Texas turtlegrass and the
effects of dredging on intercoastal channel. Publ. Inst. Mar. Sci.
Univ. of Texas 9:45-58.
Oppenheimer, C. H. 1963. Effects of Hurricane Carla on the ecology of
Redfish Bay, Texas. Bull. Mar. Sci. 15:59-72.
Orth, R. J. 1973. Eenthic infauna of eelgrass, Zostera marina, beds.
Chesapeake Sci. 14:258-269.
Orth, R. J. 1975. Destruction of eelgrass, Zostera marina, by the cownose
ray, Rhinoptera bonasus, in the Chesapeake Bay. Chesapeake Sci.
16:205-208.
Orth, R. J. 1976. The demise and recovery of eelgrass, Zostera marina, in
the Chesapeake Bay, Virginia. Aquat. Bot. 2:141-159.
Orth, R. J. and H. H. Gordon. 1975. Remote sensing of submerged aquatic
vegetation in the lower Chesapeake Bay, Virginia. Final Report
NASA-10720. 62 pp.
Orth, R. J., K. A. Moore and H. H. Gordon. 1979. Distribution and abundance
of submerged aquatic vegetation in th lower Chesapeake Bay, Virginia.
EPA Final Report 600/8-79-029/SAV1. 219 pp.
Phillips, R. C. 1972. Ecoiogical life history of Zostera marina L. in Puget
Sound, Washington. Ph.D. Dissertation, University of Washington,
Seattle, Washington. 154 pp.
Phillips, R. C. 1974a. Temperate grass flats. Pp. 244-299 jjn H. T. Odum,
B. J. Copeland and E. A. McMahan (eds.), Coastal Ecological Systems of
the United States: a source book for Estuarine Planning, Vol. 2.
Conservation Foundation, Washington, D. C.
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Phillips, R. C. 1974b. Transplantation of seagrasses with special emphasis
on eelgrass, Zostera marina. Aquaculture 4:161-176.
Phillips, R. C. 1980a. Role of seagrasses in estuarine systems.
Proceedings of the Gulf of Mexico Coastal Ecosystems Workshop.
FWS/OBS-80/30. pp. 67-96.
Phillips, R. C. 1980b. Seagrasses and the coatal marine environment.
Oceans 21:30-4C .
Phillips, R. C. and C. P. McRoy. 1980, Handbook of seagrass biology: an
ecosystem perspective. Garland STPM Press, New York. 353 pp.
Phillips, R. C., M. K. Vincent and R. T. Huffman. 1978. Habitat development
field investigations, Port St. Joe seagrass demonstration site, Port St.
Joe, Florida: Summary Report. Tech. Kept. D-78-33. 52 pp.
Ranwell, D. S., D. W. Wyer, L. A. Boorman, J. M. Pizzey and R. J. Waters.
1974. Zostera transplants in Norfolk and Suffolk, Great Britain.
Aquaculture 4:185-198.
Resmussen, E. 1977. The wasting disease of eelgrass (Zostera marina) and
its effects on environmental factors and fauna. Pp. 1-51 in C. P. McRoy
and C. Helfferich (eds.), Seagrass ecosystems: a scientific perspective.
Marcel Dekker, Inc., New York.
Renn, C. E. 1936. The wasting disease of Zostera marina L. II. A
phytoiogical investigation of the diseased plant. Biol. Bull.
70:148-158.
Robilliard, G. A. and P. E. Porter. 1976. Transplantation of eelgrass
(Zostera marina) in San Diego Bay. N.U.C. Tech. Notes 1701. 36 pp.
Solorzano, L. 1969. Determination of ammonia in natural waters by the
phenolhypochlorite method. Limnol. Oceanogr. 14:799-801.
Thayer, G. W. and R. C. Phillips. 1977. Importance of eelgrass beds in
Puget Sound. Mar. Fish. Rev. Paper 1271. Pp. 18-22.
Thayer, G. W., D. A. Wolfe and R. B. Williams. 1975. The impact of man on
seagrass systems. Amer. Scient. 63:288-296.
Thomas, L. P., D. R. Moore, and R. C. Work. 1961. Effects f-f Hurricane
Donna in the turtlegrass beds of Biscayne Bay, Florida. Bull. Mar. Sci.
Gulf and Caribb. 11:191-197.
Thorhaug, A. and C. B. Austin. 1976. Restoration of seagrasses with
economic analysis. Env. Cons. 3:259-267.
Tutin, T. G. 1938. The autecology of Zostera marina in relation to its
wasting disease. New Phyto. 37:50-71.
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vanBreedveld, J. F. Transplanting of seagrass with emphasis en the
importance of substrate. Fla. Mar. Res. Publ. No. 17, 26 pp.
Wilson, D. P. 1949. The decline of Zcstera marina L. at Salcombe and its
effects on the shore. J. Mar. Biol. Ass. U.K.. 28:395-412.
Zieman, J. C. 1972. Origin of circular beds of Thalassia
(SpermatophytatHydrocharitaccae) in South Biscayne Bay, Florida, and
their relationship to mangrove hammocks. Bull. Mar. Sci. 22:539-574.
149
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CHAPx£R 5
REGROWTH OF SUBMERGED VEGETATION
INTO A RECENTLY DENUDED BOAT TRACK
by
Kenneth A. Moore
and
Robert J. Orth
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"1
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ABSTRACT
Patterns of regrowth of the submerged macrophytes,Zostera marina and
Ruppia maritima into a recently denuded boat track were observed during a
seven month period. Revegetation occurred primarily by lateral growth
fvom the unimpscted vegetation at the sides of the cut with R.. maritima
being the more rapid colonizer. Growth from Z^ marina seedlings observed
during the fall months while ^. raarina shoots not completely removed from
the sediment by the boat propellor served as other foci for regrowth
throughout the study period. Analysis of the sediments both inside and
outside of the cut revealed little difference in the sediment grain size
or pore water nutrient concentrations,indicating that the sediment
characteristics were probably not a factor limiting regrowth into the denuded
area. It is suggested that recolonization of a one meter wide boat track
by II. maritima will take at least two seasons while recolonization by Z_.
marina will take three or more years.
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INTRODUCTION
Beds of submerged vegetation are directly disturbed in many ways by
man's activities (Zieman, 1976; Churchill et al., 1978). Dredging and
filling associated with a need for deep water access to upland development
projects may cut directly through established grass beds. In many cases,
especially in the Chesapeake Bay region, proper planning in conjunction with
both federal and state regulatory procedures can reduce or eliminate these
impacts. Illegal dredging or other inadvertant disturbances are not as
readily controlled.
Such inadvertant disturbances as boat tracks are commonly observed
throughout the beds of submerged vegetation found in the lower Chesapeake Bay
(Fig. 1). Although isolated events, in many instances they may significantly
alter the bottom in areas where boating traffic is highest, primarily during
April to October. These denuded tracks are primarily caused by propellers
digging into the bottom while vessels traverse the beds during low tidal
periods. The denuded areas can vary greatly in size, from a few decimeters
to over a meter in width, and from a few meters to many hundred meters in
length. The size is dependent upon a number of factors such as water depth,
vessel size and operator concern or awareness.
Zieman (1976) indicates that in southern Florida physical damage from
motor boats on turtle grass beds (Thalassia testudinum) persists from 2 to 5
years and that new vegetative growth by Thalassia into the cuts is very
limited. He indicates, however, that Jones (1968) and Phillips (1960) report
rapid recolonization by Halodule beaudettei in areas where it co-occurs with
Thalassia. There is little reported evidence on patterns and mechanisms of
regrowth onto similar denuded tracks found in the eelgrass (Zostera marina)
and widgeon grass (Ruppia maritima) dominated beds which are found throughout
the lower half of the Chesapeake Bay.
The object of this project was to observe the natural regrowth of
vegetation into a boat track in a bed of submerged vegetation in the lower
Chesapeake Bay. A large boat track was observed in May 1980, to have been
formed across a SAV bed in the Brown's Bay region of the Mobjack Bay since a
previous month's visit to the site in April 1980. The bed is approximately
500 m wide at this location and is part of a fringe of grasses found in the
shallow «2 m) littoral zone of the Mobjack Bay (Orth et al., 1979). Ruppia
maritima dominates the shallow inshore zone «-40 cm, MLW at this area) with
Zostera marina dominating the deeper offsnore Dories (>-80 cm, MLW).
Intermediate depths (-40 to -80 cm, MLW) are characterized by a mixture of
the two species (Orth et al., 1979).
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^^^--^1* . *~ 4<;-;-^$»' #-\ ••••3Pr *< * *"
^'ISWRggte'* -„ -%iV,-'" •%*• '=* S?^ t, ** * -,« -^ 1W^/.
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Reproduced from
best available copy.
Fig. 1. Brown's Bay, Virginia, SAV bed showing evidence of boat tracks.
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Thi boat track, when first observed, averaged approximately 1 m in width
and extended in nearly a straight line for over 200 m throughout the mixed
zone of the bed. It was oriented in nearly a 45° angle with the shoreline
that is composed of an extensive saltraarsh dominated by Spartina
alterniflora. Considering the size of the denuded area and the depth of
water (-0.5 to -0.75 m, MLW) the cut was probably formed by a commercial crab
potter or haul seiner with a moderately sized (30 ft.), inboard powered,
dead-rise type vessel. Early in the season each year, crab potters place
their pots largely within the grass beds of the Mobjack Bay. As a result,
many of these beds are crisscrossed with unvegetated paths caused by heavy
boating activity (Orth, 1976).
MATERIALS AND METHODS
Two approaches were used to monitor the regrowth of vegetation into the
denuded boat track. In the first, a one meter square reference plot was
staked out in the denuded area where the cut was found to be exactly one
meter wide. Monthly observational data was obtained by a diver including
percent of bottom revegtated, length and pattern of regrowth into the plot,
recolonization by seedlings, etc. In addition, replicate sediment cores were
obtained for analysis of particle grain size and interstitial nutrients both
within the reference plot and one meter on either side of the cot ?n the
unimpacted, vegetated area. The sediment cores were obained on June 11,
1980, and were repeated for particle size analysis only en November 23, 1980,
at the end of the study period reported here. In addition to the data
obtained on the reference plot, general observations were made by a diver at
approximately monthly intervals over the entire length of the boat track.
Such data included patterns of revegetation, changes in bottom by scouring or
bioturbation, changes in orientation of cut, etc. cs well as other
qualitative observations. Temperature, salinity and PAR light readings were
also obtained.
The sediment cores were obtained by use of 5 cm O.D. plexiglass core
tubes 50 cm in length and graduated in cm increments. The tubes were forced
into the bottom to a depth of approximately 30 cm, plugged with a rubber
stopper and pulled from the bottom with the core tube containing the
sediment, the vegetation (if present) and the overlying water. The tubes
were capped ct the top and bottom while still submerged and removed to a
covered container filled with ambient temperature seawater. Immediately
after all samples were taken the core tubes were returned to the lab for
extraction.
Upon return to the lab each core tube was uncapped at the top and 100 ml
of the overlying water extracted using a large hypodermic syringe with an
attached 0.45 vi fiber filter in a filter holder. The filtrate was placed in
a 50 ml plastic, conical centrifuge tube with a screw cap and immediately
frozen for later analysis. The sediment plug, including plant shoots, roots
and rhizoi— •*, was extruded from the core tube onto a graduated holder and
sectioned into 0-2, 2-J, 5-10, 10-15 cm depth segments. Each segment of plug
sediment was placed in a Oelman filter centrifuge tube holder and centrifuged
for 10 minutes through a 0.45 v giase fiber filter. The filtrate was
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transferred to a 50 ml capped centrifuge tube and innediately frozen. In
addition, the sediments of each depth interval of each core were placed in
Whirl-paks and immediately frozen for later grain size analysis through
standard pipette and dry sieving techniques (Folk, 1961). Pore water from
each segsaent and the sample frota the overlying water were analyzed for NH^*,
NC>3~, NC>2~ and P04~^ using automated analysis techniques (EPA, 1974) with a
technitron auto-analyzer. Modifications to these techniques were made after
Wetzel et al., 1979, including concentration of nitrate/nitrite reagents, a
two reagent chemistry for phosphate determination and a two reagent chemistry
for phosphate determination and a two reagent chemistry for ammonia
(Solorzano, 1969; Koroleft, 1970; Gravitz and Gleye, 1975; Liddicoat, Tibbits
and Butler, 1975).
RESULTS AND DISCUSSION
Observations made during th • May 23, 1980 visit to the Brown's Bay area
revealed that the entire length of the denuded boat track, including the test
plot (Fig. 2), was characterized by the presence of only a few scattered
Zostera marina seedlings and small patches of Z_, marina shoots growing from
remaining sections of rhizomes. Apparently the boat propeller had
effectively uprooted nearly all the Z_. marina. Similarly, there was
virtually no Ruppia maritima within the denuded zone. There were however,
numerous examples of new growth of R.. maritima spreading from the adjacent
vegetation portions of the bed. The growth consisted of straight rhizome
runners up to 15 cm in length with njw shoots at several cm intervals. In
contrast, there was very little evidence that 7-_. marina was spreading froa
the adjacent vegetated areas.
Triplicate 0.033 m^ cores were taken from an adjacent unimpacted section
of the Brown's Bay submerged grass bed on May 19, 1980. Complete data froa
this sampling are presented in Chapter 1 of this report. The data indicate
aseans of 100 g/m2, 76 g/m2 and 136 g/ta2 for standing stock of Zostera marina
vegetative shoots, reporductive shoots and roots and rhizomes, respectively.
Total Ruppia maritima standing stock was found to average 24 g/m'. Assuming
that these data are representative of the vegetation that would have been
growing within the denunded area at this time and that the area itself
measured 2CO ra x 1 a, then a dry weight standing stock of approximately 20 kg
of Z. marina vegetative shoots, 15 kg of Z_. marina reproductive shoots, 27 kg
of Z. marina roots and rhizones and 5 kg of R_. maritima shoots, roots and
rhizomes were essentially missing in May 1980 as a result of an apparent
single pass by a motor boat in April 1980. These equate for Z,. marina to
nearly 340,000 vegetative shoots and 85,000 reproductive shoots. Although
data on densities of _R. maritima shoots are not available for this Brown's
Bay area, calculations were made using a shoot density to total biomass ratio
determined for a similar mixed species zone at a Vaucluse Shores sampling
station (Chapter 1). They indicate that approximately 1.2 million]*.
maritima shoots could have been gr< rfing during May 1980, in this now denuded
1 x 200 m boat track.
The bottom within the track during May was for the most part quite flat
in cross sectional view. In most areas of the cut, including the 1 m2
Ib5
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""• ; • -- , ^ f \
1 - • ' ~ ~ - - ' ;>;•• -
--- — «.~;n^ «;^>,.~«si,*«.^™_™_^,™.— _ . ..._ . __.
I '1
i
!
• 25 50 75cm 25 50 75c-n
1 1 1 - 1 1 1 -»
A 1 1 1 £ fe L *- 1 • — |
1 ^ '
'' .^B
1. i
1
1 1 . ,,
DENUDED BOAT
TRACK
MAY 23, 1980
? i
I7 1*
«" k r
1 \\^Zm'Rm
\J ^
ii A
\W
(
1
III-.
» 1 1 1 A J
1 ,v.
1 »
kit/
1
1 1 • . ,
,a y^ o_
\ . /^
\ ffm\
Rm \
l\ ^ JLJUL
\ TO
A
> ^ ^ ^
.If, /
Zffl.ffal
in x
»f> J.
L
r **> v
t'l r
/ V /
Rm t /
t- V
i <
SEPTEMBER 17, 1980
» 1 1 \.ff(" <
\ *
) x xv "
r /•
v
7 V lr X
/ If /?/>; «" (-
* \
x x
** *
t X x
•j
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r j
»rr i
;
.
Z/», #/n
i
•
1
i
»
.1 :
i-Zm, Rrn
\
JUNE 24, 1980 NOVEMBER 23, 1980 :
1
m r ' ' '
1 .(/,
i — ^
* Zm,Rm j
> ItfK L
i 7 *
IV y An
it,
:i
Rm .
9
i Rm f
i
Uf * Ruppia mantima (Rm}
Vf*'
i /
VU Zostero marina (Zm)
xf
I-, * Zosfera Seedlings
,r*
i
-4
AUGUST 12,1980
!• V
Fig. 2. Regrowth of submerged vegetation into the test plot.
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reference area, the bottom vms of similar depth to the adjacent, unimpacted
bottom although at several locations it did appear that seve-al cm of sand
had been removed or eroded from the cut. After intensive storm events,
however, similarly formed boat tracks have been observed to lose considerable
amounts of material through scour by wave and current action (personal
observation). This condition would be more similar to what Zieman (1976)
observed in his study of Thalassia testudinum beds.
In numerous areas along the edges of the denuded cut and adjacent to the
existing vegetation, 10 to 20 cm diameter holes had been excavated to depths
of 15 to 20 cm. These holes which extended under the Zostera marina and
Ruppia maritima exposing both roots and rhizomes, were apparetly dug by both
blue crabs and toadfish. Orth (1975) reported similar features in
artificially clipped plots within comparably vegetated beds in this region.
Particle size distribution, in percent, for the sediments within the
0-2, 2-5, 5-10 and 10-15 depth intervals ae presented in Table 1 and
statistical parameters of grain size in Table 2 for replicate cores taken
both inside and outside of the cut on June 11, 1980. Graphic mean (M2) and
median (Md) measures of average size indicte that sediments are quite similar
with respect to depth. Although the use of only replicate sampling did not
allow for a good measure of variance, ANOVA ravealed no significant effect of
deptu and no difference between inside and outside of the boat track. Core
tl taken outside the boat track did snow a larger percent of material in the
0 phi size class of the 0-2 cm core section. There is little to suggest from
these data that now there was a significant effect of the boat propeller on
the sediment. The inclusive standard deviation or sorting coefficient (aj)
indicates that the sediments are mode <*tely sorted at all depths both inside
and out'ide of the track. The inclusive graphic skewness measure (Skj)
reveals the sediments to be fine-skewed to strongly fine-skewed with no
effect of depth or location. These results are in contrast to data of Zieman
(1976) who suggests a decrease in fine material (4 phi) in a single boat
track as compared to the unaffected Thallasia testudinum bed. It would appear
that the considerable mechanical disturbance of the boat propeller which was
capable of removing nearly 100 percent of the vegetation had little
observable effect of the grain size distribution of the sediments by June
1980.
Entractable interstitial nutrient concentrations for the sediraert cores
are presented in Table 3. Data for ammonium indicate higher levels at depths
below 10 cm within the boat track when compared to outside. This suggests
that ammonium produced by mineralization of organic nitrogen plus other
processes may be accumulating due to lack of uptake by plant roots. Reduced
levels of ammonium in the surface layers both within the outside of the
denuded track relative to the submerged layers suggest oxidation of ammonia
to nitiite and nitrate may be occurring at these shallow depths. Diffusion
of ammonium into the water column would alto contribute to reduced
concentrations nearer the surface. Lower levels of ammonium in the 0-2 and
depth segments were found inside the boat track as compared to outside.
Greater perturbation of surface of the sediments within the denuded cut by
waves or organisms such as blue crabs, etc. might lead to greater losses of
the ammonium when compared to the more protected vegetated areas. The
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TABLE 1. PARTICLE SIZE DISTRIBUTION, (%) FOR SEDIIfENT CORES TAKEN INSIDE
AND OUTSIDE OF BOAT TRACK, 6-11-80.
Depth (mm) 1.000
Core (cm)
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TABLE 2. STATISTICAL PARAMETERS OF GRAIN' SIZE FOR SEDIMENT CORES TAKEN
INSIDE AND OUTSIDE OF BOAT TRACK, 6-11-80.
Core
Out-1
it
ii
it
Out-2
ti
ii
it
In-1
„
II
II
In-2
ii
•I
it
Depth
(era)
0-2
2-5
5-10
1C-15
0-2
2-5
5-10
10-15
0-2
2-5
5-10
10-15
0-2
2-5
5-10
10-15
Mean
(Mz)
2.6
2.1
2.1
2.1
2.3
2.2
2.2
2.1
2.0
2.1
2.1
1.9
2.2
2.1
2.0
2.1
Median
(Md)
2.5
2.0
2.1
2.1
2.3
2.2
2.1
2.0
1.9
2.0
2.1
1.8
2.1
2.0
2.1
2.0
Sorf ing
(01)
1.00
0.92
0.76
0.76
0.77
0.76
0.74
0.77
0.72
0.80
0.85
0.77
0.71
0.74
0.77
0.80
Skewness
(SKj)
+0.12
+0.35
+0.23
+0..3
+0.10
+0.31
+0.16
+0.32
+0.46
+0.27
+0.18
+0.30
+0.39
+0.30
+0.28
+0.27
.<- ',;.-. ".JJ
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TABLE 3. SEDIMENT PORE WATER NUTRIENT CONCENTRATIONS (pM) IN CORES TAKEN
INSIDE AND OUTSIDE OF BOAT TPACK, 6-11-80.
Core Depth
(cm)
Out 1 water
" 0-2
2-5
5-LO
10-15
Out 2 water
" 0-2
" 2-5
5-10
11 10-15
In 1 water
" 0-2
2-5
5-10
10-15
In 2 water
" 0-2
" 2-5
" 5-10
" 10-15
mj
1.16
41.5
62.8
59.4
64.3
0.70
25.6
44.1
51.2
38.2
0.44
8.88
54.1
151
135
0.34
15.7
17.9
49.8
133
NO"
0.04
2.38
<0.01
0.25
0.04
0.07
7.07
5.40
3.29
2.38
0.08
5.48
0.82
1.64
3.95
0.08
5.49
<0.01
<0.01
<0.01
N0~
0.16
1.56
1.48
1.40
1.65
0.20
4.93
2.48
1.56
1.48
0.16
5.10
1.48
1.56
1.82
0.21
2.74
1.23
1.23
1.48
•V3
0.58
4.23
8.99
0.39
9.31
0.61
17.3
18.5
12.9
11.0
0.36
9.31
6.70
15.6
16.4
0 36
4.94
4.66
2.34
6.62
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characteristic tan color of the oxidized horizon was observed to depths of
3 cm in the boat track but only 1 cm in the vegetated area.
Data for nitrate and nitrite indicate highest concentrations in the
0-2 cm layers. This seems reasonable assuming these levels are largely
products of the upward diffusion and oxidation of arsaOiiium as described by
Gambrull and Patrick (19/8) for flooded soils. Lower concentrations for
these inorganic nitrogen species are observed below 2 cm depths. This may be
attributed to the lack of nitrification as well as to their loss under these
reduced conditions through the denitrification pathway as molecular nitrogen
or nitrous oxide. In contrast to the reduction in aaaonium levels, there
appears no evidence that concentrations of nitrate are lower in the vegetated
area below 5 cm depths when compared to the unvegetated boat track.
Inorganic phosphorus concentrations in the sediments were relatively
constant with depth and we were unable to observe a gradient between the
deeper anaerobic sediments and the oxidized surface horizons. This is not
unexpected since, as described by DeLaune, Patrick and Brannon (1976),
phosphate is not directly involved in oxidation-reduction reactions in
flooded systems, but its solubility is related to the state of the
ferrous/ferric iron system as well as other factors.
We cculd find little difference between concentrations of extractable
phosphate in the sediments of the vegetated cores taken outside the boat
track and the unvegetated cores taken within. Potentially, phosphate levels
in the interstitial water could be less in the vegetated cores due to plant
uptake of precipitation as insoluble ferric phosphate around the oxidized
rhizosphere. Lack of a significant difference between the two areas suggests
that during this sampling period the sediments were supplying adequate
phosphate to overcome any plant uptake or precipitation.
On June 24, 1980, observations made along the boat track revealed that
Ruppia maritima had rapidly extended from the side of the cut and in several
areas had expanded up to one third of the distance across the track. In
contrast to the straight rhizomes observed in May, the Jl. maritima had
branched out to form small patches of vegetation 15 to 20 cm in diameter.
Zostera marina was scattered but very sparse in abundance throughout the boat
track. The Z. marina consisted mainly of isolated rhizome segments several
up to 20 cm long but most less than 10 cm in length with 3 to 4 vegetative
shoots. They appeared to be formed primarily from the growth of sections of
rhizome not completely removed by the boat's propeller as well as from
seedling growth.
The bottom topography of the denuded zone was much more irregular than
that observed in May. There were many more depressions, some apparently
recently dug by blue crabs, with nearly vertical sides and depths to 10 cm.
Others appeared to be older snd had filled in to varying degrees. Each had a
characteristic mound of sand piled adjacent to the hole, a result of the
digging activity (Orth, 1975; Dunnigton, 1956). Adjacent vegetated areas had
similar holes scattered throughout but in greatly reduced density. It
appeared that the Zostera marina and Ruppia maritima rhizome mat was an
effective inhibitor of the digging activity (Orth, 1977).
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The sediment surf~.ce within the boat track was also littered with mats
°f Zostera marina shoots. Most were the typical sloughed off, brownish,
vegetative leaves. However, sorre consisted of whole green planes, apparently
recently uprooted, complete with rhizomes. Since the flowering, period for Z_.
marina had just ended, a few decaying reproductive shoots were located,
although no see-'s were found :i the spathes. Much of this detrital material
had accumulated in the numero. s depressions in the bottom and in many
instances was being covered by sand from the slumping of the sides of these
holes.
We observed a significant expansion of Ruppia maritima into our test
plot during this period from the adjacent vegetated zones (Fig. 2). The
recolonization was characterized by new growth at three locations extending 5
to 25 cm from the sides of the cut as straight rhizomes with a few lateral
branches. No significant revegetation by Zostera marina was evident. A crab
hole approximately 10 cm in diameter by 10 cm deep had been dug in the center
of the plot but otherwise the ploc had been undisturbed.
On August 12, 1980, the boat track was characterized by large amounts of
detrital Zestera marina vegetative shoots and Ruppia maritima reproductive
shoots covering the bottom. This detrital material was found throughout the
vegetated portion of the bed but was readily accumulated in the narrow, open
boat track to thicknesses of 5 to 10 cm. The £. marina within the bed was
experiencing its typical, midsummer die-back and the leaves were heavily
encrusted with thick deposits of epiphytic diatoms as well as algae, bacteria
etc. as described by Sieburth and Thomas (1973) and Jacobs and Noten (1980).
These heavily encrusted leaves are readily broken off. The _R. maritima,
although not as heavily entrusted as the "L_. marina, was characterized by
numerous long (1 m) reproductive shoots, m».ny of which had been shed and were
littering the bottom in much the same manner as the Z. marina reproductive
shoots had been found the previous month.
The bottom within the boat track was .nuch more regular in cross
sectional view than that found during June, with fewer crab holes and other
depressions. Revegetation by the lateral spreading of Ruppia maritima from
adjacent vegetated areas onto the denuded boat track was continuing. In
several areas, patches of II. maritima spreading from adjacent vegetated areas
onto the denuded boat track was continuing. In several areas, patches of II.
maritima spreading from both sides of the cut had nearly joined together,
although in most sections I*, maritima had revegetated 30 to 50 cm from the
sides of the boat track. In contrast to the adjacent, undisturbed portions
of the bed no reproductive shoots were observed among this new growth.
Revegetation by Zostera marina was again much less pronounced than that of R.
maritiina. There appeared to be fewer patches of "L. marina within the denuded
track during this July period than there was in June and regrowth was limited
to a few areas where encroachment was only to 5-10 cm in width.
The one meter square staked area demonstrated the continued re-growth of
Ruppia maritima across the boat track (Fig. 2). Nearly continuous bands of
regrowth extending 50 cm from one sioe of the cut and 30 cm from the other
were observed. As with other revegetated areas within the boat track no
reproductive shoots were found. In contrast to the Ruppia maritima, Zostera
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marina again showed little evidence of extensive regrowth. In only one area
did the Z_. marina spread from the adjacent vegetated zone, and then for only
a distance of 5 cm. The crab hole observed in this reference area in June
had filled in and was not evident in August.
On September 17, 1980 observations made along the boat track revealed an
apparently reduced growth race by Ruppia inaritima during the August-September
period as compared to the July-August and June-July periods. In most
sections of the denuded zone R_. maritima was covering one-third to one-half
of the originally impacted bottom. This is quite similar to observations
made during the previous month. In several sections however, R.. maritima
patches from both sides r>f the cut had joined together to completely cover
the bottom. In August these areas had not quite grown together. Regrowth of
Z_. marina, in comparison, was still characterized by only small isolated
clumps of vegetation, either as monospecific stands or mixed with the more
rapidly spreading jl. maritima which had extended from the sides of the cut.
Little significant spreading by the "L. marina was evident. Similar to
observations made during August, abundant detrital Z. marina and R^. maritima
shoots were found throughout the bottom.
The staked one meter square reference area showed reduced coverage by
Ruppia maritima when compared to the August observations (Fig. 2), but
moderate expansion by Zostera marina was observed. This compares with an
annual secondary period of growth observed for Z_. marina in this region
(Section 1). Along the west side of the cut a small area of Z_. marina had
extended an additional 5 cm from the edge of the vegetated, unimpacted ».one.
Along the east side several shoots of Z^. marina were observed for the first
time but only 2 cm from the side of the cut.
Final observations on the regrowth of the submerged vegetation into the
boat track that is presented in this report were taken on November 24, 1930,
six months after the initial sampling period and approximately saven months
after the cut was made. At this time the boat track was still well defined
and largely unvegetated. The bottom showed little evidence of active
bioturbation by large organisms in contrast to the previous summer months.
Little scouring of the boat track was evident with depths in the cut nearly
comparable to the adjacent unimpacted areas. Wave-formed ripples
approximately 2 cm high and at 10 cm intervals were evident throughout the
unvegetated bottom.
Revegetation of the boat track was still quite limited.
>ia maritima
was observed to have spread completely across the cut at only three points
throughout its 200 m length and appeared less dense than during September.
In most areas the _R. maritima was found to extend only 10 to 40 cm from the
sides of the cut. There were however small isolated patches of R. maritima,
consisting of 10 to 15 shoots, scattered throughout -he unvegetated zone.
These were probably remnants of jl. maritima which had spread from the sides
of the boat track as opposed to new growh surrounding Jl. maritima seedlings.
There were however numerous Zostera marina seedlings found for the first
time throughout the boat track. For the most part they ranged from 5 to 8 cm
in height and contained 2 to 3 leaves per plant. Z_. marina seeds in this
1
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regnn are found to germinate beginning in the fall and continuing throughout
the winter into the spring months (Chapter 3).
The spreading of Zostera marina from the sides of the cut did not appear
significantly greater than in September. In one ar»" of the boat track.
spreading Z_. marina had reached 40 cm from the edgt ^,f the cut, but otherwise
it appeared the 7^. marina had intruded on the average only 5 to 10 cm.
The one meter square test plot paralleled the observations made for ihe
entire boat track. The Ruppia maritima was reduced in coverage over that
observed in September while the Zostera marina had not significantly expanded
its coverage. Twelve "L. marina seedlings were found within the plot. This
compares with a mean of 66 per m^ found in the interior portion of a nearby
Z_. marina bed in February 1980. Z, marina seedlings of course are quite
variable in their distribution, however as the winter continues, we would
expect more and more seedlings to be found.
Visual analysis of replicate sediment cores taken in November 1980,
revealed both cores within the boat track were characterized by light tan
sand to depths of 2 to 3 cm below the surface. Below this layer the sediment
appeared of similar consistency to that above but was characterized by a grey
color indicative of anaerobic conditions. Each core taken within the cut
also had a 2 cm horizon, located at a depth of 10 cm, which contained
decaying Zostera marina and Ruppia maritima roots and rhizomes as well as
polychaete tubes and other organic matter. This loose material appeared to
have been buried at this depth and no other roots or rhizomes were obse--ved
above or below in these cores. At approximately 20 c-s of depth a
characteristic distinct layer of sandy—clay was found. In one of the two
cores a sample of this sediment found between .18 to 23 cm was analyzed for
grain size.
Visual analysis of the two cores taken in the adjacent vegetated area
revealed that a layer of light tan colored sand extended only to a depth of
1 cm. Below this, grey sand was found to approximately 20 cm depths where
the increase in clay was evident. In contrast to the cores taken in the boat
track, no distinct horizon or organic matter was found, however viable
Zostera marina and Ruppia maritima roots and rhizomes were observed to 10 cm
depths throughout the cores.
Particle size distribution in percent, for the 0-2, 2-5, 5-10 and
10-15 cm depth intervals of the sediment cores are presented in Table 4.
Statistical parameters of grain size are found in Taole 5. The 18-23 cm
depth segment from core #2 taken inside the boat track reveals the
characteristic sandy-clay layer found throughout this region. The fines
(<5 phi) predominate in this layer, thus increasing the median and mean phi
sizes significantly compared to the overlying sediments. The skewness measure
for this layer of sediment indicates the grain size distribution to be
otrongly coarse-skewed. This is somewhat misleading in that the skewness is
relative to the tnean grain size which is much finer than the other sediment
samples.
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TABLE 4. PARTICLE SIZE DISTRIBUTION (%) FOR SEDIMENT CORES TAKEN INSIDE AND
OUTSIDE OF BOAT TRACK, 11-23-80.
Core
Out-1
It
It
»
Out- 2
ii
«
It
In-1
«
»
II
In-2
"
11
ii
11
Depth
(cm)
0-2
2-5
5-10
10--15
0-2
2-5
5-10
10-15
0-2
2-5
5-10
10-15
0-2
2-5
5-10
10-15
18-23
(nan) 1
«!
0
0
0
0
0
0
0
0
0
0
1
3
0
0
0
0
1
.000
0
.49
.70
.50
.56
.70
.41
.60
.23
.11
.15
.J6
.6S
.21
.07
.10
.57
.59
1
0
1
2
2
1
1
0
1
1
2
5
0
1
1
3
1
.500
1
.22
.78
.37
.21
.07
.10
.54
.82
.65
.72
.58
.16
.95
.56
.63
.05
.50
.250
2
14
12
14
17
20
14
21
12
20
34
22
24
18
29
20
26
6
.66
.07
.69
.62
.75
.17
.44
.81
t
.71
.04
.76
.96
.77
.02
.51
.25
.04
.125
3
62.52
65.19
67.44
63.95
59.60
61.27
61.69
64.92
.;
62.78
55.58
57.91
46.86
72.96
61.03
60.45
58.16
37.04
.063
4
4.65
3.88
3.27
4.20
3.24
5.21
3.18
'4.74
2.87
2.01
'•4.26
2.49
2.86
2.42
3.41
2.39
4.49
<•
16
17
12
11
< 13
17
11
16
i
11
6
11
16
4
5
13
9
49
063
5
.44
.36
.73
.46
.63
.83 -,
.55
.48
.89 •
.50
.43w
.84
.25
.91
.90
.57
.34
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TABLE 5. STATISTICAL PARAMETERS OF GRAIN SIZE FOR SEDPIENT CORES TAI'.EN INSIDE
AND OUTSIDE OF BOAT TRACK, 11-23-80.
Core Depth
(cm)
Out-1 0-2
2-5
5-10
10-15
Ovt-2 0-2
" 275
5-10
"* 10-15
In-1 0-1
" 2-5
" 5-10
10-15
In-2 0-2
2-5
" 5-10
10-15
" 18-23
Mean
(MJ
2.8
2.9
2.5
2.4
2.5
2.9
2.4
2.9t
2.4
2.2
2.4
2.6
2.4
2.3
2.6
2.3
3.4
Median
(Kd)
2.6
2.6
2.5
2.4
2.4
2.6
2.4
2.6
2.4
2.2
2.4
2.4
2.4
2.3
2.4
2.3
3.7
Sorting
(oD
0.92
0.90
0.67
0.73
0.80
0.92
0.74
0.88
0.73
0.73
0.80
1.29
0.57
0.69
0.83
0.78
0.94
Skewness
+0.31
+0.31
+0.11
+0.02
+0.17
+0.29
+0.12
+0.36
+0.11
+0.17
+0.04
+0.13
+0.11
+0.09
+0.21
+0.06
-0.48
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Comparisons between the sediments in the boat -.rack and those in the
adjacent, undisturbed bed suggest an increase in th i fine fraction ("C5 phi)
in the top 5 era in the bed. Both mean and median statistics as well as the
skewness measure also indicate a slight decrease in grain size in the surface
layers. The particle size distribution as well as the statistical parameters
indicate little apparent change with depth for sediments inside the boat
track. Considering the large maount of bioturbation observed throughout the
summer months, this homogeneity is not unexpected. Zieman (1976) indicates a
slight decrease in fine laaterial (4 phi) in a single boat track and a
considerable decrease in fines in one continually kept open from repeated
scouring by small boats. He did not indicate however, the depth to which his
samples were taken. Most probably the slight differences observed in our
study area between the vegetated and unvegetated zones are the result of
insufficient wave and current scouring actions, baffled in part, by the
existing vegetation adajcent to the denuded cut. Whatever the actual
differences however, they do not appear after seven months to be sufficient
to inhibit the revegetation by the submerged grasses.
CONCLUSIONS
Patterns of revegetation of the boat track observed in this study
indicate that in a mixed assemblage of Zostera marina and Ruppia maritima it
is _R. maritima that is the more rapid colonizer. Revegetation by II. matitima
and "L. marina occurred primarily as lateral growth from the unimpacted
vegetation at the sides of the cut although any vegetation, either Z_. marina
or jl. maritima, which is not completely uprooted by the boat propeller may
serve as a focal point for new growth. Zostera seedlings were obsserved in
the fall throughout the boat track and their presence indicates a potentially
important mechanism for revegetation.
Analysis of sediment data indicate that the sediments both inside and
outside of the boat track dominated by fine sands and are fairly homogeneous
to depths of approximately 20 cm. Active bioturbation of the sediments
appears a likely mechanism for this homogeneity. The urooting of the
vegetation by the boat propeller therefore initially had little net effect on
the grain size of the sediments. After seven months however, theu was some
evidence that in the top 5 cm there were finer particles outside the boat
track than inside.
Extractable sediment pore water nutrient concentrations suggest
comparable levels of inorganic phosphorus both inside and outside cf the cut
with little observable change with deprh. Nitrate and nitrite levels were
highest in the top 2 cm of sediment, due possibly ot oxidation of ammonium,
with no significant difference between the vegetated and unvegetated areas.
Ammonium levels were, conversely, lowest in the top 2 cm and appeared to have
accumulated to higher levels below 5 cm depths inside the boat track when
compared to outside. It would not appear from these data that differences in
sediment nutrients were limiting the vegetative regrowth into the cut.
The more rapid regrowth observed in this study for Ruppia maritima as
compared to Zostera marina parallels that observer by Jones (1968) and
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Phillips (1960) for Halodule wr ight ii as compared to Thalassia testudinum.
Seven monchs after the disturbance, however, the R. n.aritima had spread over
less than half of the 1 m wide denuded zone. Since R^. maritima experiences
little net growth during the winter months at this latitude, it would appear
that at least two growing seasons may be required for recolonization by JR.
maritima. Recolonization by Z_. marina appears to take significantly longer.
Certainly little rogrowth was evident during the study period. This suggests
that three year* or more are required for revegetation, with a part of the
regrowth a result of recruitment by seedlings and relic turions not
originally removed from the sediment. These time intervals appear comparable
to those suggested by Zieman (1976) for ]j_. wr i gh t i i and 1_. jestudinuin.
Considering the patterns of revegetation observed in this study, in
mixed areas of Zostera marina and Ruppia maritima succession after a physical
disturbance proceeds from a JJ. maritima community to a II. maritima-Z. marina
community. It is not uncommon in many areas to observe homogeneous stands of
JR. maritima in otherwise mixed zones of submerged vegetation. Possibly these
patches of vegetation are sites of previous physical distrubances from boat
propellers, ray activity, etc. that have been initiflly recolonizjd by JR.
maritima.
Patterns of revegetation may vary from site to site and season to season
depending on a number of factors. Because of Ruppia maritima's less
extensive rhizome mat as compired tc Zostera mar'.na, souring by wave action
during severe storm events may selectively uproot the JR. maritima leaving
largely Z_. marina. At other times both species may be removed. The period
when a disturbance occurs also can impact the intitial revegetation
successional stages. Disturbances during the fall may result in little
regrowth for th<=>. next six months. If severe storm activity occurs during the
winter months, erosion of these areas unprotected by the rhizome mats may
preclude revegetation for quite some time. In extreme conditions heavy
boating activity combined with highly exposed conditions may result in the
permanent loss of vegetation.
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REFERENCES
DeLaune, R. D., W. H. Patrick, Jr. and J. M Brannon. 1976. Nutrient
transformation in Louisiana salt marsh soils. Sea Grant Publication Ko.
LSU-T-76-009. Louisiana State University, Baton Rouge, LA.
Dunnington, D. A. 1956. Blue Crab observed to dig soft shell clams for
food. Maryland Tidewater News 12: p. 1.
Folk, R. L. 1961. Petrology of Sedimentary Rock. Hemphillis, Austin, TX.
154 pp.
Gambrell, R. P. and W. H., Patrick, Jr. 1978. Chemical and microbiological
properties of anaerobic soils and sediments. Pp. 375-423 in_ Plant Life
in Anaerobic Environments. Ann Arbor Science, Ann Arbor, MI.
Gravitz, N. and L. Gleye. 1975. A photochemical side reaction that inter-
feres with the phenolhypochlorite assay for ammonia. Limnoi. Oceanogr.
20:1015-1017.
Jacobs, R. P. W. H. and T. M. P. A. Noten. 1980. The annual pattern of the
diatoms in tha epiphyton of eelgrass (Zostera marina L.) at Roscoff,
France. Aquat. flot. 8:355-370.
Jones, J. A. 1968. Primary productivity by the tropical marine turtle
grass, Thalassia testudinum Konig and its epiphytes. Dissertation,
Univ. of Miami, Coral Gables, FL. 196 pp.
Koroleff, F. 1970. Direct determination of ammonia in natural waters as
indophenol blue. Pp. 19-22 jj> Information of Techniques and Methods for
Seawater Analysis. ICES, Service Hydroraphique.
Liddicoat, M. I., S. Tibbitts and E. I. Butler. 1975. The determination of
asntonia in seawater. Limnoi. Oceanogr. 20:131-132.
Orth, R. J, 1975. The role of disturbance in an eelgrass (Zostera marina)
community. Ph.D. Dissertation, Univ. of Maryland, College Park.
115 pp.
Orth, R. J. 1976. The demise and recovery of eelgrass, Zostera marina in
the Chesapeake Bay, Virginia. Aquat. Bot. 2:141-159.
Orth, R. J. 1977. The importance of sediment stability in seagrass
communities. Pp. 2C1-300 ir± B. J. Coull (ed.), Ecology of Marine
Benthos. Univ. South Carolina Ptess, Columbia.
169
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Orth, R. J., K. A. Hoore and H. H. Gordon. 1979. Distribution and
abundance of submerged aquatic \egetation in the lower Chesapeake Bay,
Virginia. Final Report. U.S. EPA Chesapeake Bay Program
600/8-79-029/SAV1. 199 pp.
Phillips, R. C. 1960. Observations on the ecology and distribution of the
Florida seagrasses. Prof. Pap. Ser., Fla. Board Conserv. 2:1-72.
Sieburth, J. McN. and C. D. Thomas. 1973. Fouling on eelgrass (Zostera
marina L.). J. Phycol. 9:46-50.
Solorzano, L. 1969. Determination of ammonia in natural waters by
the phenolhypochlorite method. Limnol. Oceanogr. 14:799-801.
Zieman, J. C. 1976. The ecological effects of physical damage from motor
boats on turtle grass beds in Florida. Aquat. Bot 2:127-139.
170
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CHAPTER 6
GROWTH OF ZOSTERA MARINA L. SEEDLINGS UNDER
LABORATORY CONDITIONS OF INCREASED NUTRIENT ENRICHMENT
Morris H. Roberts, Jr.
Robert J. Orth
and
Kenneth A. Moore
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ABSTRACT . ~
The effect of increased nutrient on growth of Zostera marina seedlings
was laboratory tested by adding two different concentrations of a slow
release fertilizer, Osmocote. Three different application rates were used \~
with the two formulations (18:6:12 and 14:14:14) of Osmocote by hand placing >
these amounts into peat pots holding one seedling.
The addition of fertilizer to the substrate markedly stimulated the "^
growth of seedlings in the laboratory. Fertilization promoted growth both in - *
the increased leaf length and in vegetative production of increased number of
shoots but did not result in an increase in the leaves/shoot. The nitrogen
rich formulation (18:6:12) produced less growth than the equal balance
formulation (14:14:14). Fov both formulations, the highest concentrations • •
exhibited greater growth than the other concentrations of the same ~"^?
formulation. Results of this experiment corroborated results from previous .^
work suggesting that addition of nutrients in the sediment can stimulate >
growth and seagrasses are nutrient limited in some types of sediments. .!./
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INTRODUCTION
Laboratory culture of Zostera marina is essential for some types of
experimental studies of life-history, physiology, growth, and reproduction
and potentially has value for production of plants to reestablish grass beds
in denuded areas. In both cases, it is desirable to know how fertilization
affects growth under controlled conditions. Fertilization of marsh plants
and seagrass under field conditions is known to stimulate growth (Raymont,
1947; Buljan, 1957; Valiela. 1975; Valiela et al., 1973, 1976; Valiela and
Teal, 1974; Garbisch et al., 1975; Orth, 1977; Orth and Moore, 1982) but
effects under laboratory conditions have not bean studied previously.
The objective of the experiment described here was to evaluate the
effect of two fertilizers at several concentrations on growth of seedlings
under laboratory conditions. The experiment was preliminary in nature since
no information on laboratory culture of seedlings was available on which to
base a refined experimental protocol.
MATERIALS AND METHODS
Seedlings for this xperiment were collected 11 March 1980 from a grass
bed at Guinea Marsh, Yor': River, Va. Seedlings were manually uprooted by
divers and collected in plastic oags.
Soil for the experiments, was collected from the same site as the
seedlings and placed in 5 x 5 cm square peat ^ots supported in plastic
greenhouse trays. A sediment core was removed from selected pots. The core
in a Gelman filter centrifuge tube (0.45 pm glass fiber filter) was
centrifuged for 10 minutes. The filtrate was analyzed for NHj*, N02~> N03~
and P04~ with a Technicon Autoanalyzer II (Kopp and McXee, 1979). The core
sample represented 21J of the total sediment and pore water in the peat pot.
Seedlings were planted in the peat pots and held in flowing estuarine water
for two weeks. Seven groups of 52 seedlings were then selecred on 20 March
1980 for the experiment.
The fertilizers selected for the experiment were two formulations of
Osmocote®, one with a N:P:K ratio of 18:6:12, the other 14:14:14. Osmocote
was selected because it is a slow release fertilizer. No attempt was made to
determine whether there was a slow release of the fertilizer under the water
logged conditions of the experiment. It was assumed that all nitrogen and
phosphorus were released in a form available to the plants. Each fertilizer
was applied at three application rates (g/m*) (Table 1). Application rates
for each formulation of Osmocote were calculated to provide the same three
amounts of total nitrogen; 12.5, 25, and 50 g/ra^. The appropriate amount of
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TABLE 1. SUMMARY OF FERTILIZER APPLICATION RATES. SEDIMENT NITROGEN AND
PHOSPHORUS CONCENTRATIONS WERE CALCULATED FROM APPLICATION RATE
AND CONCENTRATION IN FERTILIZER ASSUMING TOTAL AVAILABILITY OF
BOTH NUTRIENTS
Treatment Fertilizer
A
B
C
D
E
F
G
None
14:14:14
14:14:14
14 : 14 : 14
18:6:12
18:6:12
18:6:12
Application Rate
(g/m^) (g/peat pot)
0
89.3
178.6
357.1
69.4
138.9
277.8
0
0.23
0.46
0.91
0.18
0.35
0 71
Nitrogen
g/m^
0
12.5
25
50
12.5
25
50
Phosphorus
g/m2
0
12.5
25
50
4.2
8.3
16.7
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fertilizer was placed on the sediment surface of each peat pot and tamped
into the substrate while the pot was in the air. Pots were immediately
returned to the holding tank receiving flowing water. Another group of
plants which received no fertilizer served as the control. Crude dividers
(fiberglass) were placed in the holding tank to segregate all treatments.
The holding tank was located in a greenhouse and received about 50% incident
light at the water surface.
Ambient estuarine water was pumped from the York River, Va. and filtered
to 10 pm with GAF filter bags. Flow rate was adjusted to insure several
volume turnovers per day. Despite filtration the water in the holding tank
was turbid because fine particles predominated in the incoming water. Actual
light intensity at the sediment surface of the peat pots was not measured,
but was presumed equal for all treatments. Any shading effects of the '.
holding tank were not controlled.
The day following fertilization the number of leaf blades/plant and
length of longest blade were determined and recorded. At two week intervals
thereafter, the plants were wiped gently with fingers to remove detritus and
epiphytes. Number of shoots, leaf blades/shoot, and length of longest blade
on oldest shoot were determined. The seventh and final measurement was made ,,
on 13 June 1980. V
Leaf bladr. lengths for each treatment were compared for each measurement ' i
interval by one-way analysis of variance and Duncan's multiple rsnge test. ,;
Number of leaf blades/plant and number of shoots were analyzed by
nonparametric methods. All statistical analyses were performed using SAS
packaged programs on the William and Mary IBM computer system.
RESULTS
During the acclimation period and the first growth interval, the
temperature averaged 10.3° and 10.8°C respectively while salinity declined
from 17.8 to 15.7 °/oo (Table 2). Mean temperature increased in each
succeeding growth period to 27.3*C during the final interval. Salinity
declined to 14.9 °/oo during the third growth interval, and then increased to
17.9 °/oo during the final period. Throughout the study, dissolved oxygen
measured by Winkler titration during the midday period usually exceeded
saturation. The most extreme value was 27.4 mg/1 observed on 7 June.
Observed oxygen concentrations exceeded saturation in 92% of the observations
over the entire study period. Supersaturation is believed to have resulted
from the photosynthetic activity of the Zostera plants plus that of the
diatoms and other microphytes growing wit'nir. che system. The extreme values
of dissolved oxygen during the final growth period resulted largely from the
microphytes since Zostera growth was reduced.
The measured concentrations of each inorganic nitrogen form and total
phosphorus, in micromoles, are presented in Table 3 for prefertilization
samples and samples collected at the end of the 12-week growth period.
Ammonia was the principal form of nitrogen present both before and after
fertilization whereas nitrite was present in extremely small amounts. In all
175
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TABLE 2. MEAN TEMPERATURE, SALINITY AND DISSOLVED OXYGEN CONCENTRATIONS DURING
ACCLIMATION AND GROWTH PERIODS FOR ZOSTFRA GROWTH/FERTILIZATION STUDY.
T (rC)
mean SD
S
mean SD
D.O. (rag/1)
mean SD
over-saturation
frequency percent
acclimation period
1 III - 4 IV
5 III - 18 IV
19 IV - 2 V
3 V - 16 V
17 V - 30 V
3 V - 13 VI
10.3 ± 2.6 17.82 ± 0.56 1.1.50 ±1.13 5/6 83
10.8 ±2.1 15.67 ±0.69 12.40 ±2.29 10.13 77
14.3 ± 1.3 15.83 ±0.76 13.09 ±3.21 12/14 86
19.6 ± 2.0 14.86 ± 0.28 14.10 ±2.92 14/14 100
22.3 ± 3.5 15.41 ± 1.24 13.01 ± 5.26 13/14 93
23.8 ± 1.3 15.97 ±0.77 12.00 ± 3.43 12/12 100
27.3 ±1.5 17.91 ± 1.03 18.93 ± 3.95 11/11 100
7778492~
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TABLE 3. KUTRIENT CONCENTRATIONS (yra) IN SEDIMENT PORE WATER BEFORE AND AFTER
THE GROWTH PERIOD.
Treatment Nlty* N03~ N02~ P04~3
3/24/80
Prefertilization
6/17/80
Post Growth
Control
14:14:14
1A : 14 : 14
14:14:14
18:6:12
18:6:12
18:6:12
A
B
C
D
E
F
G
204
10300
4460
4990
5675
7450
5220
4400
+_ 46
+_ 6590
+_ 1150
+_ 1130
+_ 3180
+_ 5240
+_ 1150
+_ 950
1.97
1290
366
493
594
1100
1430
245
+_ 0.59
+_ 924
+_ 203
_+ 208
*_ 198
_+ 1560
_* 2090
jf 64
0.83
1.60
1.30
0.20
1.05
1.44
1.14
0.62
+_ 0.49
+_ 0.88
+_ 1.77
i 0.18
+_ 0.25
+_ 0.36
+_ 1.07
+_ 0.48
41.1
0.74
14.6
42.5
42.9
5.7
16.3
27.1
jf 27.4
+_ 1.28
+ 8.1
+_ 31.1
± 30.4
±4-7
i 10.8
+_ 8.5
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treatments including the control, ainmonia-N and nitrate-N concentrations in
the sediment were greatly elevated above those observed prior to
fertilization. Sedimentary phosphorus concentrations after the growth period
were below those observed prior to fertilization in all but two cases
(Treatments C and D). The standard deviations for all samples were large.
At the start of the experiment, each seedling consisted of a single
shoot with an average of 4.1 leaves/shoot (maximum of six leaves/shoot). The
number of shoots/plant increased slowly during the experiment until, at the
end of the study, the mean numbers of shoots/plant were 1.2 in the control
and from 2.8 to 3.5 in the fertilized groups (Fig. 1). After four weeks, a
few control plants developed three shoots but at no time did more than 12% of
the control plants have three shoots, while 65% of the control plants still
had only one shoot. By the end of the growth period, 84% had only a single
shoot (Table 4).
In all experimental groups, the number of plants with three shoots
increased throughout the experimental period. After 6 to 8 weeks, some
plants would develop four or morj shoots per plant (Table 4). At the end of
the 12 week study period, 30-47% of the plants fertilized with 14:14:14 and
21-28% of the plants fertilized with 18:6:12 had four or more shoots
(Table 5). The tendency for production of multiple shoots was clearly
enhanced when plants were fertilized, and especially so when 14:14:14
Osmocoat was applied.
The maximum number of leaves/shoot observed during the experiment was
eight, but usually shoots had four to six leaves. At the start of the
experiment the mean number of leaves/shoot was 3.8-4.3. The mean number of
leaves/shoot was not obviously different at the end of the study (3.7-4.4).
No attempt was made to monitor sloughing of leaves.
The average length of the longest leaf (hereafter referred to as average
leaf length) was 8.6 to 9.2 cm at the start of the experiment and increased
throughout the study period. The average leaf lengths were not significantly
different among the treatments until after 4 weeks growth (Table 6) but,
thereafter, three to four groups of treatments were definable by a Duncan's
multiple range test. After 8 weeks, all experimental treatments were
significantly different froa the control group and assorted into two groups:
treatments B, C, D, and G exhibiting greater average leaf length than
treatments E and F. The latter difference was much smaller than the
difference from the control group.
The growth increment for each time interval was calculated as the
average leaf length at time (t+1) minus the average leaf length at time
(Table 7). The initial growth increment was small, increased to a maximum in
interval 2 and 3, and then declined. During the final interval, growth had
almost ceased in those treatments receiving the most fertilizer, and was very
low in controls and all other treatments. Greatest overall growth increments
occurred in the treatments receiving the highest amounts of fertilizer.
The mean leaf length for each treatment was plotted against nitrogen
applied at the start of the experiment (Fig. 2A). Tht treatments receiving
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_- cvJ
•H
01
w *O
o c
(0
C cd
HJ O
CJ 1-1
60
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TABLE 4. NUMBER OF SHOOTS/PLANT AT 1HE END OF EACH GROWTH PERIOD.
Growth
Period
(weeks)
2
4
6
8
10
12
2
4
6
8
10
12
2
4
6
8
10
12
2
4
6
8
10
12
2
4
6
8
10
12
2
4
6
8
10
12
2
4
6
8
10
12
Number of Shoots
Treat. 1
A 43
32
34
33
38
41
B 35
22
16
14
5
4
C 40
30
21
14
8
4
D 35
18
16
15
9
5
E 27
14
15
16
5
4
F 29
25
20
20
12
5
G 33
29
24
21
15
6
2
7
13
9
14
9
6
16
21
20
23
22
5
9
14
19
18
16
9
11
19
20
17
11
5
14
22
18
18
20
13
17
14
14
16
16
13
16
14
18
16
20
11
3
4
6
2
2
2
1
8
15
11
15
26
3
4
11
15
16
4
10
10
12
15
15
3
8
6
6
12
16
7
9
6
10
13
1
7
5
8
8
21
456
2
7 1
9 4 1
1
2
4 2
11 2 3
1
2 1
641
10 6 6
4
3
4 2
721
1
1
3 2
561
3
311
9
Number
of
7 8 Plants
50
49
49
49
49
49
52
51
51
50
50
1 50
49
47
45
45
45
45
50
47
47
47
46
47
44
44
43
43
43
43
46
46
44
43
43
43
50
50
48
48
48
1 48
Mean Number of
Shoots/Plant
1.1
1.4
1.4
1.4
1.3
1.2
1.4
1.7
2.0
2.0
2.5
3.2
1.2
1.4
1.7
2.0
2.5
3.2
1.4
1.8
1.9
2.1
2.7
3.5
1.5
1.9
2.0
1.9
2.5
2.8
1.4
1.6
1.8
1.7
2.2
2.9
1.4
1.6
1.6
1.9
2.1
2.8
180
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TABLE 5. PERCENTAGES OF PLANTS WITH EACH OBSERVED
SHOOTS/PLANT AFTER THE 12 WEEK GROWING
PERIOD .
Number of Shoots/plant
Treatment 1234+
Control A 84 12 40
14:14:14 B 8 10 52 30
C 9 20 36 36
D 1J 11 32 47
18:6:12 E 9 30 37 23
F 12 30 30 28
G 13 23 44 21
181
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TABLE 6. COMPARISONS OF AVERAGE LEAF LENGTH FOR EACH TREATMENT
AT EACH TIME INTERVAL. VALUES UNDERLINED WERE NOT
SIGNIFICANTLY DIFFERENT BASED ON DUNCAN'S MULTIPLE
RANGE TEST.
TIME
0 wks
2 wks
4 wks
6 wks
8 wks
10 wks
12 wks
G
9.2
E
11.4
E
17.7
G
26.4
G
29.0
D
33.2
D
33.4
B
9.2
C
11.2
G
17.6
C
24.3
D
28.8
G
32.7
G
32.8
C
9.1
D
11.0
D
17.3
D
23.9
C
28.0
C
31.J
B
31.9
D
9.1
G
11.0
C
17.1
E
21.9
B
26.3
B
30.6
C
31.8
A
8.8
B
10.9
B
i6.0
&
21.7
E
25.1
F
28.7
E
29.1
F
8.7
A
10.8
r
15.7
F
2) .'j
F
24.8
E
28.2
F
29.0
E
8.6
F
10.7
A
14.9
A
17,1
A
18.0
A
20.3
A
2i.5
182
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TABLE 7. BI-WEEKLY GROWTH INCREMENTS (cm) IN AVERAGE LEAF LENGTH DURING
EACH GROWTH INTERVAL.
Growth period (wks) Overall
Treatment 2 4 6 8 10 12 Total
Control 2.0 4.1 2.2 0.9 2.3 1.2 12.7
14:14:14 12.5 gN/m2 1.7 5.1 5.7 4.8 4.1 1.3 22.7
25 2.1 5.9 7.2 3.7 3.1 0.7 22.7
50 1.9 6.3 6.6 4.9 4.4 0.2 24.3
18:6:12 12.5 2.8 6.3 5.2 2.2 3.1 0.9 20.5
23 2.0 5.0 5.6 3.5 3.7 0.3 20.3
50 1.8 6.6 8.8 2.6 3.7 0.1 23.6
183
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14:14:14 Osmocoat (treatments B, C, and D) exhibited better growth than did
those receiving 18:6:12 Osmocoat (treatments E, F, and G) except at the
highest application rate. The raean leaf length for each treatment was also
plotted against the amount of phosphorus applied at the start of the
experiment (Fig. 2B). Leaf length increased with increasing application rate
of phosphorus up to 16.7 g/m^. Clearly, at equal application rates of
nitrogen, less growth occurred in the treatments receiving less phosphorus.
Increased applications of nitrogen had little effect on leaf length.
DISCUSSION
x In his discussion of the seasonal pattern of the life cycle of Zostera
marina, Setchell (1929) identified five seasonal segments for growth and
reproduction. These segments are Da cold rigor period at temperatures
below 10°C, 2) a vegetative period from 10-15°C, 3) a reproductive period
from 15-20*0, 4) a heat rigor period at temperatures above 20°C, and 5) a
recrudescent rigor period as temperatures decline below 20°C. The present
growth study spanned temperatures from 10°C to 27°C, thus covering the first
four seasonal segments. During the first growth period when temperatures
hovered around 10°C, growth occurred at a slow rate. Maximal growth occurred
during the next two periods when temperatures increased to about 20°C,
corresponding to Setchell's seasonal segments 2 and 3. Sexual reproduction
was not observed, but was not expected since seedlings do not reproduce
sexually. Vegetative reproduction (production of new shoots) was observed
during all periods of the experiment, but was especially pronounced during
the first 4 weeks (temperature 10.8 to 14.3°C) and the final 4 weeks
(temperature 23.8 to 27.3°C) (Fig. 1). As temperatures exceeded 20°C, leaf
growth continued as well as vegetative shoot addition, but at a slower rate,
and as the temperature increased over 25°C, growth nearly ceased.
There was no trend in mean number of leaves/shoot or maximum
number/shoot at any time during the study. New leaves were continuously
appearing on each shoot, but after five or six appeared, the rate of new leaf
addition was about equal to the loss of old (outer) leaf blades so that the
leaves/shoot remained constant. Total leaves/plant increased simply because
the number of shoots increased over the study period from around four at the
start to an average of about 12 after 12 weeks, though plants with seven
shoots might have 28-30 leaves.
Several conclusions can be drawn from this study. Obviously, addition
of fertilizer to the substrate markedly stimulated growth of seedlings in the
laboratory. This agrees with observations of enhanced growth of Zostera in
natural beds fertilized with commercial fertilizers (Orth, 1977). More
recently, Orth and Moore (1982) have shown that fertilization enhances
survival and growth of transplanted Zostera plugs. Fertilization promotes
growth both in the sense of increased leaf length and in vegetative
production of increased number of shoots, but does not lead to an increase in
leaves/shoot. Orth and Moore (1982) also reported a striking increase in
number of shoots in fertilized transplants ot Zostera.
185
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X-
With respect to increased leaf length, the nitrogen-rich phosphorus-poor
formulation (18:6:12) produced less growth than the equal balance formulation
(14:14:14). For both formulations, the highest concentrations produced
greater growth than the other concentrations of the same formulation. Only
the 50 g/m2 application rate of 18:6:12 formulation yielded growth in leaf
length equal to that observed in plants receiving the 14:14:14 formulation.
The production of multiple shoots/plants was pronounced in all
fertilized groups. Only 42 of the control plants exhibited three
shoots/plant whereas more than 60% of all fertilized plants exhibited three
I or more shoots/plant; indeed more than 20% exhibited four or more
| shoots/plant. With the 14:14:14 formulation 30 to 47% of the plants had four
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I or more shoots/plant, the proportion increasing with increasing application
" rate. For the nitrogen-rich formulation, 21 to 28% of the plants possessed
four or c'ore shoots/plant, but there was no clear relationship to application
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186
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REFERENCES
Buljan, M. 1957. Report on the results obtained by a new method of
fertilization experimented in the marina bay Mhjetska Jesera. Acta
Adreat. 6:1-44.
Garbisch, E. W. , Jr., P. B. Waller, W. J. Bostian, and R. J. McCallum.
1975. Biotic techniques for shore stabilization, pp. 405-426. In; E.
L. Cronin (ed.) Est. Res., Vol II. Academic Press, New York.
Kopp, J. F. and G. D. McKee. 1979. Methods for chemical analysis of water
and waste. U.S. EPA, EPA 600/4-79-020.
Orth, R. J. 1977. Effect of nutrient enrichment on growth of the
eelgrass Zostera marina in the Chesapeake Bay, Virginia, USA. Mar,
Biol. 44:187-194."
Orth, R. J. and K. A. Moore. 1982. The effect of fertilizers on
transplanted eelgrass, Zostera marina L. in the Chesapeake Bay. In; R.
Stovall (ed.), Proc . of the North Annual Conference on Wetlands
Restoration and Creation. Hillsborough Community College, Tampa,
Florida. (In press).
Raymont, J. F. G. 1947, A fish farming experiment in Scottish sea
locks. J. Mar. Res. 6:219-227.
Setchell, W. A. 1929. Morphological and phenological notes on
Zostera marina L. Univ. California Publ. Bot. 14:389-452.
Valiela, I., J. M. Teal, and N. Y. Persson. 1976. Production and
dynamics of experimentally enriched salt marsh vegetation: below-ground
biomass. Limnol . and Oceanogr . 21:245-252.
Valiela, I. and J. M. Teal. 1974. Nutrient limitation in salt marsh
vegetation, pp. 547-563. JCn: R. J. Reiraold and W. H. Queen (eds.)
Ecology of Halophytes. Academic Press, New York.
Valiela, I., J. M. Teal, and W. Sass. 1973. Nutrient retention in
salt marsh plots experimentally fertilized with sewage sludge. Est.
Cstl. Mar. Sci. 1:261-269.
Valiela, I., J. M. Teal, and W. J. Sacs. 1975. Production and
dynamics of salt marsh vegetation and the effects of experimental
treatment with sewage sludge. J, Appl. Ecol. 12:973-982.
187
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