United States
Environmental Protection
Agency
Environmental Research
Laboratory
Narragansett Rl 02882
Research and Development
EPA-600/S3-83-082 June 1984
4>EPA Project Summary
Effects of Thermal Additions on
the Dynamics of Fouling
Communities at Beaufort,
North Carolina
W. W. Kirby-Smith
The effects of long-term, low-level
thermal additions on recruitment and
structure of the marine epibenthic
community were investigated in a
laboratory system maintained at 0°C
(an unheated control), 2°. 4°C, or 6°C
above the ambient temperature. Com-
munities developed on ceramic tile
plates over a three-year period were
sampled nondestructively at monthly
intervals for percent cover by individual
species. Recruitment also was assessed
monthly. The experimental system
modified the laboratory communities
compared to those on field plates,
enhancing the recruitment of some
species and decreasing or eliminating
others. The laboratory communities
were composed of epifaunal species
common in North Carolina.
Thermal addition had a pronounced
effect upon recruitment of certain
species and on species number and
diversity on the permanent community
plates, but had little effect on the
community type. The laboratory com-
munities were dominated by the oyster
Crassostrea virginica and the polychaete
Spirorbis borealis. Temperature eleva-
tions of 2°C produced measurable
effects on recruitment and percent
cover by individual species; these
effects were more apparent at the 4°C
and 6°C elevations. Community com-
plexity was markedly reduced by
elevations of 6°C in midsummer when
the 36°C temperature apparently ex-
ceeded thermal limits of many species.
Caution is urged in applying these
findings to the field or using them for
regulatory decision making; i.e., this
experimental system is limited in
simulating the natural environment.
Additionally, it is possible that certain
temperature responses observed may
be unique to this particular fouling
community.
This Project Summary was developed
by EPA's Environmental Research
Laboratory. Narragansett. Rl. 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
The purpose of this investigation was to
determine the consequences of long-
term, low-level elevations intemperature
on larval recruitment and to observe
community development and structure of
the marine epifaunal (fouling) community
at Beaufort, North Carolina. The project
represents one approach to the study of
sublethal consequences of thermal
additions by estuarine and coastal power
plants.
The literature concerning effects of
temperature on marine communities has
been developed primarily from investiga-
tions of unnatural thermal discharges
from steam electric stations. Field studies
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have been very useful in understanding
the effects of thermal additions in a
general sense; however, it is often
difficult from field studies alone to
quantify the biological consequences of
specific levels of thermal elevation,
particularly those of a sublethal nature. In
addition, a good record of the tempera-
tures actually experienced in the field is
rarely available.
Quantitative information on thermal
effects is important for power plant siting
and design and for environmental regula-
tory uses. Controlled laboratory studies
resulted in more precise examination of
the relationships between elevated
temperature and biological effects. Most
of the studies tested single species. The
applicability of the results to the field
often has been constrained by such
limitations as the short duration of the
study, the use of unusually high tempera-
tures, an inability to test for full life cycle
effects, or difficulties in predicting the
community level consequences of such
tests. A long-term laboratory study with a
natural assemblage such as the fouling
community is an approach that should
overcome many of these limitations.
Wolfson (1974) conducted a laboratory
study of the effects of temperature on a
fouling community at Scripps Institution
of Oceanography. Unfiltered coastal
seawater was pumped through four
aquaria in an open-flow system. Two
aquaria were unheated controls; thethird
was maintained continuously at 3°C
above ambient temperature, and the
fourth was cycled with six-hour intervals
at 3°C above ambient followed by six-
hour intervals at ambient. Asbestos
plates were suspended in the tanks in
March to encourage development of the
fouling community which was observed
for one year. The response of individual
species to elevated temperature varied
from positive to negative effects on
recruitment and growth, depending upon
which species was considered. In the
summer, when water temperatures were
highest, survival was reduced in a
number of species. Species exposed to
the cycling thermal regime were much
less affected than those exposed to
constantly elevated temperature. Com-
munity species diversity was similar in all
treatments in the spring. During the
summer, there was a decrease in
diversity of both elevated temperature
tanks. In the fall, the diversity of the
communities exposed to the cycling
temperatures was similar to those in the
ambient temperature treatment, but
diversity in the constantly heated treat-
ment remained depressed. The results of
2
the experiments by Wolfson agreed with
this study's observation at field sites
experiencing thermal addition. However,
Wolfson's experiments were of short
duration relative to the time required for
complete fouling community development;
nor did they address community changes
caused by the experimental system perse
in the absence of thermal additions.
Moreover, seawater temperatures in
southern California cycle over a range of
approximately 12°C (12°C-24°C), while
temperatures of the bay and estuarine
waters along the mid-Atlantic cycle over
a range of 25°C (5°C-30°C).
Methodology
Two aspects of community dynamics,
recruitment of species and development
of the community, were followed over a
three-year period under field conditions
and in an open-flow laboratory seawater
system with continuous temperature
elevations of 0°C (no heat added), 2°C,
4°C or 6°C above the ambient seawater
temperature. The community was defined
as those species which were recruited
and grew on the underside of continuously
submerged, unglazed ceramic tile plates
(232 cm2). Field plates were located 0.3 m
below mean low water near the seawater
intake at the Duke University Marine
Laboratory, Beaufort, North Carolina;
laboratory plates were submerged in
tanks supplied with constantly flowing,
temperature controlled, seawater. Com-
munities developed from planktonic
larvae which settled on these plates. For
each month of the study, changes in
community structure on permanent
community plates were followed by
nondestructive point sampling to deter-
mine the percent cover of individual
species; at one-month intervals, recruit-
ment was determined by enumerating all
identifiable individuals on larval recruit-
ment plates which had been submerged
throughout the preceding one month.
Experiments were conducted over the
period of November 1976 to November
1979.
Conclusions
Long-term, low-level thermal additions
produced dramatic effects on some
aspects of recruitment and structure of
the fouling community; but on other
parameters the additions produced few
effects. Within the laboratory system,
increasing temperatures resulted in a
complex of effects on the recruitment and
percent cover of individual species.
The direction and magnitude of the
effects on recruitment of species were
not often the same as those observed for
percent cover. A 2°C increase in temper-
ature resulted in significant differences
in recruitment of individual species in an
average of 40.7 percent of the cases
where significant recruitment occurred
in one or the other of the treatments
being compared. This effect increased to
53.5 percent at the 4°C differential and
62 percent at the 6°C differential. The
significant differences in recruitment
were either positive or negative, often
depending upon the species, the treat-
ment, and the time of year. For example,
the number of individuals recruited
increased in each elevated temperature
treatment for Bugula neritina and Spirorbis
borealis and decreased for Schizoporella
errata and Balanus spp. (+2, +4°C only).
From the community standpoint, increas-
ing temperature did result in a decrease
in the average number of species
recruited in the summer and in an
increase in winter. However, no temper-
ture effect on the community structure of
recruits was evident when evaluated by
cluster analysis of the average number of
individuals recruited by each species for
each treatment for the 29 sequential time
periods.
On the permanent community plates,
the average number of species and
diversity decreased with increasing
temperature; this effect was particularly
evident when comparing 6°C with 0°C
plates in midsummer. Cluster analysis of
the percent cover data for permanent
plate communities did not show a
temperature effect on community struc-
ture. This result is due mainly to the
dominance of Crassostrea virginica and
Spirorbis borealis on the community
plates in most temperature treatments.
Cluster analysis is not a good technique
for distinguishing treatment effects in
communities with only two dominants,
since the species clusters are most
affected by the presence or absence of
the dominant species and their relative
(not absolute) abundance.
A comparison of field results with
results obtained in the laboratory in the
0°C treatment (tanks with no thermal
addition) indicated that the laboratory
system itself had a large effect upon
recruitment of most species and the
development of the communities. Re-
cruitment of species on field plates and
laboratory 0°C treatment plates was
significantly different in 76 percent of the
270 cases analyzed. The pattern of these
differences was complex and varied
through time; there were positive,
negative, and neutral effects on the
number of individuals recruited. Specie^
composition of the community as deter-^
-------
mined by cluster analysis of percent cover
data also differed, with only one species
(the oyster, Crassostrea virginica) being a
significant member of both field and
laboratory 0°C communities. The per-
centage of unoccupied space was siginfi-
cantly greater on laboratory 0°C plates
than on field plates. However, the
number of species per plate and the
diversity, based on percent cover data,
were similar for field and laboratory 0°C
plates. Although the community com-
position differed, all species in both
communities were common members of
the epibenthic community in North
Carolina.
Some of the differences between the
laboratory and field communities may
have resulted from ingestion of larvae by
suspension feeders in the tank commu-
nities, as there was a large decrease in
suspended material in laboratory tanks
relative to that in the field. Analysis of
flow rates, chlorophyll a values, and rates
of suspension feeding by communities
suggested that the system was probably
food stressed during the warmer months
of the year in all temperature treatments
and throughout the year at the 6°C
differential. The laboratory system also
incompletely simulated the field in other
ways, including the absence of strong
currents, rapid turnover of water, and
pelagic predators, plus the potential for
loss of some larval recruits and food due
to damage by pumping or ingestion by
any fouling organisms in the seawater
lines and tanks.
In this study, a chronic 2°C elevation in
temperature had measurable effects on
some parameters of community develop-
ment (e.g. suppressed or enhanced
recruitment for some species and, in the
permanent plate communities, a slight
reduction in species number during
June). Increases of 4°C and 6°C caused
similar, but more pronounced effects. At
4°C, species number on the community
plates was reduced during all seasons.
At 6°C, species number and diversity
were reduced markedly, particularly in
the summer and autumn months after
ambient temperatures were the highest.
However, these findings should be
applied with caution to field or regulatory
questions concerning the consequences
of thermal additions, recognizing the
limitations of the experiment systems.
Recruitment of larvae and their subse-
quent growth and survival were probably
influenced by the experimental system, in
some ways positively and in others
negatively. The limited food supply in the
system doubtless compromised growth
and possibly survival of the oysters, one
of the two community dominants. Yet
given careful interpretation, these results
do illustrate some of the ways in which
long-term, low-level thermal addition
may alter population and community
structure of a warm temperate zone biota.
Recommendations
This study highlights two issues which
should be considered when assessing the
consequences of thermal addition for
estuarine and coastal communities. First,
conspicuous effects are most likely to
occur during the season when water
temperatures are naturally at their
maximum. To predict allowable thermal
additions during this period, an estimate
of the long-term, incipient upper thermal
limit should be experimentally determined
for the communities of concern. If
community studies are not practical,
studies should be conducted for the
community dominants. Secondly, during
seasons that the community upper
thermal limit would not be exceeded,
subtle changes may nonetheless occur.
Very low-level thermal additions (e.g.
2°C) may have little effect other than
increasing the duration and the intensity
of community spawning and recruitment.
Higher levels of chronic additions (e.g. 4°
or 6°C) may alter community structure, as
evidenced here by reductions in species
number and community diversity. The
long-term implications of such changes
for community integrity or for the
protection of populations of particular
concern will require further investigation
of the communities or species in question.
Marine epibenthic communities hold
potential as a research tool to investigate
the long-term effects of sublethal envi-
ronmental stress, including anthropogenic
perturbations of a conservative or non-
conservative nature. These communities
develop readily on clean surfaces, they
integrate natural changes in environ-
mental conditions, and their species
composition may be ascertained easily in
a nondestructive fashion. Interaction
among species is simple; it is predomi-
nantly competition for primary space.
However, there are some problems
which must be resolved when employing
the fouling community in experimental
studies. The problem of providing adequate
food may be addressed by increasing the
water exchange rates, assuring that
seawater delivery lines are free of fouling
organisms, and minimizing the biomass
in each experimental tank. Maintenance
of a strong current within the tanks may
also be considered, as this will enhance
the development of additional species
typical of this community. Other conditions
normally experienced by this assemblage
are difficult to simulate in the laboratory,
such as the presence of predators. In
order to address community questions, it
may be necessary for the study to be
conducted for more than a year, since the
epibenthic community which is initially
established may have only one dominant,
with a monoculture resulting. Given
additional time, the assemblage usually
moves towards increased diversity.
Experimental studies on communities
should employ multiple parameters to
describe community structure and deve-
lopment. In this research, one parameter
of community structure was percent cover.
No treatment effects were evident for this
parameter by cluster analysis. However,
cluster analysis is considered to be a
relatively insensitive technique for a
community having only two dominants.
In contrast, other community parameters,
such as diversity using percent cover data
and percent unoccupied space, did show
significant influence of thermal additions.
In addition, it is important to recognize
that an environmental stress (either
natural or anthropogenic) may have a
negative influence on one species or
characteristic of a community, a positive
effect on another, and no effect on a third.
Reference Cited
Wolson, A.A. 1974. Some effects of
increased temperatures on the settlement
and development of a marine community
in the laboratory. University of California
Institute of Marine Resources UC-IMR
Reference No. 74-13. 159 p.
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W. W. Kirby-Smith is with Duke University Marine Laboratory, Beaufort, NC
28516.
D. C. Miller is the EPA Project Officer (see below).
The complete report, entitled "Effects of Thermal Additions on the Dynamics of
Fouling Communities at Beaufort, North Carolina," {Order No. PB 83-260 489;
Cost: $26.00, 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:
Environmental Research Laboratory
U.S. ^Environmental Protection Agency
South Ferry Road
Narragansett, Rl 02881
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