xe/EPA
United States
Environmental Protection
Agency
Chesapeake Bay
Program
Annapolis MD 21403
Research and Development
EPA-600/S3-82-090 Jan. 1983
Project Summary
The Biology and Propagation of
Eelgrass, Zostera marina, in
Chesapeake Bay
Robert J. Orth and Kenneth A. Moore
Basic biological aspects related to
the growth and propagation of
eelgrass in the lower Chesapeake Bay
were studied in a series of six
experiments. These were designed to
reveal information on seasonal
aspects of standing crops, reproduc-
tion, transplanting, and spontaneous
revegetation in denuded areas, and
growth of eelgrass seedlings under
laboratory conditions of increased
nutrient enrichment.
Data analysis revealed distinct
seasonal trends in the growth cycle of
eelgrass. Transplantation of eelgrass
plugs in the fall insures greater
survivability than in any other season.
Lateral growth from adjacent
unimpacted areas appears to be the
primary method of revegetation by
Ruppia sp. and Zostera sp., although
seed germination and subsequent
seedling growth may be significant in
certain areas. The addition of a
balanced formulation of fertilizer
stimulates the growth of eelgrass
under laboratory conditions.
This Project Summary was devel-
oped by EPA's Chesapeake Bay Pro-
gram, Annapolis, MD, to announce
key findings of the research project
that is fully documented in a separate
report of the same title (see Project
Report ordering information at back).
Introduction
Chesapeake Bay eelgrass beds are a
valuable natural resource which
provides a habitat for large numbers of
macroinvertebrates, food for migrating
waterfowl, and shelter for juvenile
fishes and blue crabs. In addition, grass
beds aid in the reduction of shoreline
erosion by absorbing wave energy and
serving as a sediment trap. Their
contribution to the detrital food chain is
also significant.
The recent (1970s) disappearance of
eelgrass beds in the lower Bay has
prompted an interest in replanting.
Studies have shown that revegetation
under favorable conditions is feasible,
but some problems still exist because
knowledge related to eelgrass biology is
lacking. The six experiments in this
study were designed with this in mind.
Seasonal Aspects in the
Standing Crop of Eelgrass Beds
Procedure /Methodology
At three study sites in the lower main
Bay, seasonal changes in standing crop
were observed, aiding in the description
of the reproductive biology of eelgrass.
The study sites were:
1. Near the mouth of Browns Bay in
Mobjack Bay.
2. Adjacent to the Guinea Marshes
at the mouth of the York River.
3 At Vaucluse Shore at the mouth
of Hungars Creek on the Eastern
Shore.
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From June, 1978 through June,
1979, monthly ring samples were taken
at each site. A 0.1 m2 ring was placed on
the bottom and all vegetation, including
the roots and rhizomes, to a depth of
about 10 cm was removed. Beginning in
June, 1979, core samples also were
taken. A comparison of these two
procedures revealed few differences.
Six core sa mples were taken at each site
until January, 1980, when sampling
was reduced to three cores. Sample
analysis yielded information on number
of vegetative and reproductive shoots
per meter squared (m2), mean length of
shoots, biomassof the leaf, and rootand
rhizome fractions per m2. Temperature
and salinity measurements, as well as
sediment samples, were taken at each
site.
From November, 1979 to May, 1980,
monthly seedling samples were taken at
the Guinea Marsh in-shore area. These
samples were analyzed for maximum
length of the primary leaf and the
number of shoots and leaves per
seedling.
Results/ Conclusions
Each of the three sites showed similar
trends for maximum and minimum
values of parameters such as shoot
biomass, shoot density, and number of
reproductive shoots. The season of
maximum biomass for vegetative
shoots was summer; the minimum
biomass occurs in the fall or winter.
However, the maximum biomass of the
two years differed, with 1980 showing a
higher volume than 1979. This
difference seems to indicate the
presence of some environmental
control (e.g., temperature) or biological
control (waterfowl interactions) that
affects all grass-beds and can vary from
year to year.
Appearance and growth of new
shoots occurred after mid-August, and
growth continued throughout the
winter and spring. Measurements of
mean length of shoots showed a distinct
trend for all sites. Peak length occurred
in June-July for all sites except
Vaucluse Shore, which had peak length
in May, possibly as a result of tempera-
tures rising faster in this shallower
area.
The number of seedlings observed at
each site differed, probably due to seed
production differences within a
particular area and also to possible seed
dispersal from other areas.
Anthesis and Seed
Production in Zostera marina L.
Procedure/Methodology
Random samples were taken at 7- to
10-day intervals from March 11, 1980
to May 28, 1980 at three sites to
establish the timing involved in the
flowering process of eelgrass. A subset
of samples was taken beginning in
January, 1980 to ascertain the
beginning of the flowering period.
Samples were analyzed for the number
of vegetative and reproductive shoots,
length, number and position of spadices
per shoot, and number and size ranges
of anthers and pistils within each
spadix.
Results/ Conclusions
Reproductive shoots were first
observed in February, 1980. Pollen
release was first observed April 10,
1980, when the average water
temperature was 14.3°C, and was
completed at all stations by May 19,
1980. By May 28, the fruiting process
was at full maturity. The period from
pollen release to initial seed
development and release was 28 days.
This process begins and ends one
month earlier in lower Chesapeake Bay
than in areas farther north.
Seed Germination of
Eelgrass in the Lower
Chesapeake Bay
Procedure/Methodology
Beginning in late April, 1979, repro-
ductive shoots of eelgrass were exam-
ined at nine stations weekly to identify
the timing of eelgrass seed germination.
Results/Conclusions
Seed germination occurred every
month except July and August, when
temperatures were too high. The major
period of seed germination occurred
between November 1 and March 31,
when water temperatures did not
exceed 10°C. Storage of seeds at tem-
peratures above 15°C will prevent
germination but may result in rotting.
The data collected suggest that low
temperature rather than salinity maybe
the primary cause of seed germination.
Apparently, no dormant period exists
between seed release and germination.
The rate of seed germination varied
from site to site. These differences may
be the result of subtle environmental
differences in factors such as runoff,
temperature, or the depth at which
seeds are buried in the sediments.
Transplantation of Eelgrass
into Recently Denuded Areas
Procedure /Methodology
Plants were removed from an
established bed at the Guinea Marsh
area and transplanted at a site near
Mumfort Island in the York River. The
Mumfort Island area was selected
because it had been the site of extensive
eelgrass beds but was now devoid of
Zostera. In addition, the area was fairly
isolated, reducing the probability of
disturbance by people.
In March, 1979, transplanting by two
different methods (plugs and mats)
began; other transplantings were made
in early June, in September and October,
and in April, 1980. Four additional sites
were used for the transplantings made
during the latter-mentioned four
months: Gloucester Point, Aliens Island,
Guinea Marsh in the York River, and
Parrott Island in the Rappahannock
River. Fertilizer was used in some trans-
plants to assess the effect on success
rate.
Results /Conclusions
A comparison of the two methods of
transplanting (plugs and mats) indicates
that the use of plugs is the better
management option for mitigation,
especially in more wave-exposed areas.
Success of the transplants depended on
the season of planting (fall was best and
summer the least successful) and
location. Downriver sites (Guinea
Marsh, Aliens Island, and Gloucester
Point) produced better results than the
upriver site (Mumfort Island). High
temperatures and reduced available
light (especially at the Mumfort Island
site) make summer the least desirable
time for transplanting. Sites chosen for
transplants should have previously
supported Zostera. Better growth
results were obtained when Osmocote
fertilizers (14-14-14) were used in
spring, 1980 transplants at Aliens
Island.
Regrowth of Submerged
Vegetation into a Recently
Denuded Boat Track
Procedure /Methodology
Monthly observations were made on
a denuded one-meter square plot within
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a boat track to determine the percentage
of revegetation, regrowth patterns, and
seedling recolonization. Sediment
samples analyzed for particle grain size
and interstitial nutrients were taken
from this plot and an unimpacted
vegetated area.
The entire length of the boat track also
was observed monthly to determine
revegetation patterns, effects of
scouring or bioturbation, and any
changes in orientation of cut. In
addition, temperature, salinity, and PAR
light readings were taken.
Results/Conclusions
Revegetation by Ruppia and Zostera
occurred primarily as lateral growth
from adjacent unimpacted areas. Ruppia
seems to recolonize more rapidly than
Zostera. After seven months, Ruppia
had spread over less than half of the
denuded area. At least two seasons of
growth are apparently required for
Ruppia recolonization and possibly
three for Zostera.
Analyses of the sediments reveal
them to be fairly homogenous to depths
of about 20 cm, probably due to active
bioturbation. No significant differences
existed for interstitial nutrients inside or
outside the denuded area
Growth of Eelgrass Seedlings
Under Laboratory
Conditions of Increased
Nutrient Enrichment
Procedure/Methodology
Seedlings were collected from a grass
bed at the Guinea Marsh site on the
York River and placed in peat pots
containing soil from the same site. Peat
pots were placed in greenhouse holding
tanks that received flowing estuarine
water from the York River and about fifty
percent incident light at the water
surface. Two formulations of Osmocote
fertilizer were applied at three different
dosages. Number of shoots, leaf blades
per shoot, and length of the longest
blade on the oldest shoot were recorded
at two-week intervals from March 20,
1980to June 13, 1980.
Results/Conclusions
Growth by way of increased leaf
length and vegetative production of
^increased number of shoots is
stimulated by fertilizer. The balance
formulation (14:14:14) produced better
results in increased leaf length than did
the nitrogen-rich formulation (18:6:12).
Sixty percent of the fertilized plants
exhibited three or more shoots per plant
as compared to only four percent of the
controls.
Recommendations
Before 1978, little was known about
the basic biology of eelgrass. Although
this study answered some questions
about eelgrass biology, it led to the
discovery of many others which could
not be answered. Several questions that
should be addressed in future studies
are what controls maximum production
of eelgrass in a particular area, what are
the reasons for annual difference in
shoot production and biomass, what are
the temperature and salinity effects on
seed germination, and what are the
effects of fluctuating temperatures on
seed storage?
Robert J. Orth and Kenneth A. Moore are with Virginia Institute of Marine
Science, Gloucester Point, VA 23062.
David A. Flemer is the EPA Project Officer (see below).
The complete report, entitled "The Biology and Propagation of Eelgrass, Zostera
marina, in Chesapeake Bay, "(Order No. PB83-116400; Cost: $ 17.50; subject
to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Chesapeake Bay Program
2083 West Street, Suite 5G
Annapolis, MD21403
it U.S. GOVERNMENT PRINTING OFFICE: 1983 659-OI7/O889
3
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