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-^

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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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