United States
Environmental Protection
Agency
Environmental Research
Laboratory
Gulf Breeze FL 32561
Research and Development
EPA/600/S4-85/039 Aug. 1985
v>EPA Project Summary
Field Validation of Laboratory-
Derived Multispecies Aquatic
Test Systems
Robert J. Livingston, Robert J. Diaz, and David C. White
A three-year study was carried out to
determine the feasibility of using multi-
species microcosms of benthic microor-
ganisms and infaunal macroinverte-
brates to predict the responses of
estuarine systems to toxic substances.
Criteria were developed to evaluate the
field validation of laboratory micro-
cosms. Simultaneous laboratory/field
experiments were carried out in the
Apalachicola Bay system in Florida, and
the York River estuary in Virginia, to
test the potential for extrapolation of
validation results from one ecological
system to another. The study demon-
strated that microcosms of microor-
ganisms and infaunal macroinverte-
brates can be established for short
periods (5-6 weeks) and that the micro-
cosms can be used to simulate specific
features of field assemblages within
the range of uncertainty that is charac-
teristic of natural systems. Moreover,
validation results can be extrapolated
from one system to another as long as
the systems share common habitat fea-
tures and dominance relationships of
important populations.
Water quality in the microcosms' es-
sentially paralleled that in the field, al-
though variation of certain water fea-
tures and sediment characteristics was
noted. These laboratory, artifacts were
apparently caused by the isolation of
the microcosms from natural phenom-
ena of the estuarine environment that
were not replicable in the laboratory.
Physical habitat features and biological
responses in the respective study areas
were extremely complex and highly
variable in space and time. Factors,
such as water and sediment quality.
predator-prey relationships, recruit-
ment, and dominance relationships
among infaunal populations influenced
the community structure of benthic or-
ganisms in the laboratory and the field.
However, the relative influence of phys-
ical and biological factors varied con-
siderably between habitats and
through time. Consequently, the extent
to which the microcosms paralleled
field conditions depended to a consid-
erable degree on the time of testing and
dominance/recruitment features of the
system in the source area.
This Project Summary was devel-
oped by EPA's Environmental Research
Laboratory, Gulf Breeze, FL, to an-
nounce 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 basic question underlying the
considerable effort to understand
pollution-induced changes in aquatic
systems is well established: what is re-
quired to predict the environmental ef-
fects of a toxicant or stimulatory sub-
stance on a given ecological system?
With the recent development of sophis-
ticated toxicological methods to evalu-
ate acute and chronic effects of toxi-
cants on laboratory populations, the
question then becomes: what is re-
quired to establish a reliable measure of
the capability of specific laboratory test
systems to predict actual environmental
effects of a given toxic agent?
We define the process of field valida-
tion as the testing of the capacity of
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cific laboratory test systems to predict
the environmental responses of natural
ecosystems, or portions thereof, to toxi-
cants. Once a test system is validated, it
provides a means of generating toxico-
logical data that can be realistically cor-
related with expected field impacts. The
process of validation necessitates two
pursuits: selection of a particular test
system and acquisition of knowledge
about the natural variation and dynam-
ics of field populations from which the
test system is derived. Without knowl-
edge of ecosystem structure and func-
tion, it is practically impossible to evalu-
ate toxic effects.
The focus of our three-year project
has been microbial and infaunal macro-
invertebrate communities of unvege-
tated soft sediments of shallow estuar-
ies in Florida (Apalachicola Bay system;
Florida State University) and Virginia
(York River estuary; Virginia Institute of
Marine Science). Our principal objec-
tives were (a) to evaluate the capacity of
the laboratory test as a realistic analog
or simulation of the natural community
from which it was derived and (b) to
develop criteria for field verification of
laboratory results. The evaluation con-
sidered validation at three levels:
physico-chemical differences, differ-
ences in population and community
structure, and functional differences be-
tween full-field and semi-field treat-
ments and laboratory microcosms. Re-
sults of such tests are being applied to
current experiments that concern the
predictive capability of microcosms ex-
posed to toxic substances. Concur-
rently, a complete review is underway
to determine the potential for extrapola-
tion of validation results from one loca-
tion to another.
Materials and Methods
All field and laboratory operations in
the respective study areas followed
standardized methods. Aside from cer-
tain differences inherent in the two
study sites, experimental procedures
were carried out in a comparable man-
ner. Prior to the initiation of the project,
all background field data from the study
areas were updated and evaluated to
establish a preliminary protocol for the
full-laboratory, semi-field, and full-field
treatments. Based on preliminary analy-
ses of background data, the spatial lim-
its and frequency and location of sam-
pling were determined.
The study sites in the Apalachicola
Bay system (East Bay and St. George
Sound) were shallow [1-2 meters (m)],
unvegetated soft-bottom areas located
in oligohaline (stations 3, 5A) and poly-
haline (station ML) areas. Sediments in
the oligohaline areas were silty sand,
whereas sediments in the polyhaline
zone were largely fine sands (1-2% silt-
clay). The York River study site was a
shallow (1.5 m), unvegetated soft bot-
tom located in the meso-polyhaline por-
tion of the estuary.
Microcosms were constructed of a
series of cores collected with hand-
operated box corers (10 x 20 centime-
ters (cm); 10 cm deep). Core samples
were placed in trays on sea-water tables
in the same arrangement as the original
field orientation of the cores. The size of
each microcosm was 0.8 to 1.0 square
meters (m2). Light, temperature, and
salinity regimes followed field condi-
tions. Synoptic biological sampling of
microcosms and field was done ran-
domly with coring devices (5 cm, VIMS;
7.5 cm, FSU). Sieves of mesh sizes 250
and 500 micrometers ((Jim) were used
for the infaunal macroinvertebrates. Mi-
crobial samples were taken from field
areas and laboratory microcosms with a
3.2-cm-diameter corer and analyzed for
lipids and fatty acids.
Four field-laboratory experiments
were carried out over a 2-year period.
The tests were conducted during spring
and fall periods of peak biological activ-
ity and change in the respective study
sites. Although some changes were
made to the sampling program over the
study period, a basic protocol was de-
veloped and followed for experiments
at both sites. The approach was to sam-
ple replicated flow-through laboratory
microcosms (0.8-1.0 m2) derived from
natural soft-sediment areas, simulta-
neously with field treatments (exclusion
cages, inclusion cages, cage controls)
(Figure 1).
Variables analyzed during the experi-
mental series included numerical abun-
dance (total number of individuals and
dominant populations), numbers of
species, and species diversity. All analy-
ses were carried out with and without
Iog10(x+1) transformations. A nested
ANOVA analysis to test for differences
between laboratory microcosms was
carried out with 250- and 500-ji.m sieve
fractions (macroinvertebrates) and mi-
crobial parameters. To test the null hy-
pothesis that no significant difference
existed among field and laboratory
treatments with respect to the variables
listed above, selected ANOVA models
were employed. A one-way ANOVA
was run on all treatments by sampling
period. A randomized block repeated-
measures ANOVA was used with the
field data with location as the blocking
factor and time as the repeated mea-
sure. Tukey's method of multiple com-
parisons was used to test the differ-
ences between all possible pairs of
means. Analyses of qualitative changes
in infaunal assemblages were carried
out using "rho" and Czekanowski simi-
larity coefficients and the flexible grop-
ing strategy with beta = -0.25.
Results and Discussion
Experimental Program: Florida
State University
The relationship of laboratory micro-
cosms to field conditions depended on
a number of variables that changed de-
pending on time and the location of the
test. During the spring experiments in
an oligohaline area, significant differ-
ences were noted for total numerical
abundance and species richness of
macroinvertebrates because of labora-
tory artifacts in recruitment. Similar ex-
periments in the spring in polyhaline
areas led to increases of the dominant
polychaete, M. ambiseta, in the labora-
tory microcosms, paralleling changes in
the field predator-exclusion treatments.
Such changes in recruitment and possi-
ble predation effects could have led to
significant differences of various com-
munity features between the laboratory
and field assemblages of microorgan-
isms and infaunal macroinvertebrates.
The fall tests in oligohaline areas
showed significant differences between
laboratory and field treatments as a re-
sult of blooms of the oligochaete Wapsa
grandis in the laboratory microcosms.
These differences became significant
after the fifth week of testing. Fall exper-
iments in the polyhaline areas also re-
sulted in significant differences because
of low numbers of individuals and re-
duced recruitment in the laboratory
treatments relative to the field.
Factors such as spatial habitat gradi-
ents, temporal changes in population
processes, and changes in the influence
of predation pressure all contributed to
the complexity of the validation pro-
cess. Also, the initial establishment of
the microcosms and continued sam-
pling led to observed differences be-
tween the laboratory microcosms and
natural field conditions. However, the
broad spectrum of information pro-
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18 meters (59 ft)
FA - Screened Exclusion
FB = Screened Inclusion
FC - Control
FC
FA
FB
\+-4m-+\2m\
2m
FA
FA
FC
T
6m
10m
38 m
(125 ft)
Figure 1. Diagram showing placement of cages (inclusion/exclusion capes), cape controls.
and full-field sampling areas.
vided by microcosms produced indices
such as species richness that were rela-
tively conservative indicators of field
conditions. Thus, field validation of
macroinvertebrates can be qualified
within known limits of spatial and tem-
poral variability based on specific eco-
logical conditions in a given area.
The results with microorganisms il-
lustrated several points: (1) fatty acid
analysis, combined with multivariate
statistical techniques, was a powerful
means of comparing the structure of dif-
ferent microbial communities; (2) mi-
crocosms may or may not mimic natu-
ral microbial communities; and
(3) microbial communities from similar
environments but different ecological
conditions may show a wide range of
response when isolated in the labora-
tory. This technique should have great
potential in evaluating a microbial com-
munity's response to toxic substances.
The major shortcoming of the micro-
cosm approach is our current inability
to interpret the significance of changes
in particular fatty acids. Based on this
study, it can be concluded that not all
sediments will mirror the field to the
same degree when placed in relatively
complex microcosms. Our findings
showed the importance of biological
control of microbial communities in the
estuarine environment and the need to
include biological as well as physical
factors in the design of model labora-
tory systems. A priori, without knowing
the specific ecology of a particular site,
one cannot conclude that a reasonably
designed microcosm will always simu-
late the field.
Experimental Program: Virginia
Institute of Marine Science
In the context of microcosm research,
it is not necessary that we know the
causes of population fluctuation but
only that fluctuations occur. It is the in-
teractive nature of the community and
the environment that generates the fluc-
tuations we observe. So, in evaluation
of a microcosm toxicity test, it is neces-
sary to consider the broad, total-
community approach. We should avoid
singling out one species for assessing
toxicity.
Long-term population dynamics will
result in periods when any given spe-
species may be present in low abun-
dance. This would make repeated test-
ing difficult if those species in low abun-
dance were needed. Also, at any
laboratory conducting community mi-
crocosm tests, it is essential to know the
natural population fluctuations. Other-
wise, major changes in the community
associated with natural cycles would be
missed, making interpretation of micro-
cosm results difficult or misleading. The
total community represents a single en-
ergetic entity. From year to year, about
the same amount of energy flows
through the community. Although indi-
vidual species patterns are different
from year to year (and consequently the
amount of energy flowing through each
species is different), the total energy
budget is relatively constant.
The following findings exemplify the
need to consider the total system:
1. Tharyx sp. declined by a factor of
10 from 2,000 m~2 in 1983 to 200
m~2 in 1982. The Mediomastus
ambiseta population increased
from low abundances in early 1980
to peak in mid-1982 and declined
through 1983. Paranais littoralis
did not have successful recruit-
ment in 1980 or 1981, and it was
not even a community dominant
until 1982. Most of the dominant
species exhibited some year-to-
year variation that might make re-
peated testing difficult if it were
based on a single species.
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2. The major natural fluctuations in
the community were associated
with recruitment. Should the initia-
tion of a microcosm test unknow-
ingly coincide with recruitment,
populations could increase or de-
crease by orders of magnitude in
test treatments. The onset of re-
cruitment can generally be easily
identified from the size of individu-
als. It is the subsequent decline of
the recruitment peaks that could
cause problems of interpretation.
Without knowledge of the natural
timing of these declines, it might
be difficult to identify toxic effects.
The species that consistently ex-
hibited highest mortality after re-
cruitment from 1980 to 1983 were
Paranais littoralis, Streblospio
benedicti, and Heteromastus fili-
formis.
3. Overall, there was about the same
density of individuals in 1980,
1981, and 1982 (defining the year
from October to September to bet-
ter coincide with recruitment). In
1983, the density dropped by a
third. In 1980 and 1981, popula-
tions of the dominant annelids
were about the same size both
years. Based on this fact and the
assumption that total yearly pro-
duction can be partitioned be-
tween species and still remain con-
stant from year to year, it seems
likely that the total production for
the York River site was the same in
both 1980 and 1981. We have not
looked at the size of individuals in
1982 and 1983 to see whether this
is the general trend. The impor-
tance of this productivity to micro-
cosm testing is in understanding
the interactive nature of the com-
munity. If one species is in low
abundance for a given year, then
another may be more abundant
and offset the loss in productivity.
Although the community structure
changes, the functioning of the
community remains unchanged.
Microcosms need to capture this
functional response to represent
field response truly.
A broad view of all parts of the com-
munity was needed to see the relation-
ship between the laboratory micro-
cosm, which is the target of interest as a
tool to judge environmental conse-
quences of toxicants, and the field. Clus-
ter analysis indicated that during Test 1
(spring of 1982) the microcosms be-
haved very much like the field, but in
Test 3 (spring of 1983) they did not. Ap-
parently, in the spring of 1983, recruit-
ment into the microcosms was reduced
relative to the field, possibly because of
some laboratory artifact or timing of the
test relative to recruitment peaks. Re-
sults of the fall tests were consistent,
with recruitment being less in the mi-
crocosms. With this understanding that
recruitment into the microcosms will
likely be lower than in the field, because
of the nature of the test system, we can
more accurately interpret toxic effects
in the microcosms.
No one species was able to carry con-
sistently sufficient information about
the validity of the microcosm test sys-
tem. Analysis of the variation in individ-
ual species abundance within and be-
tween tests showed that most species
did not have a consistent response to
the full-field, semi-field, or microcosm
treatments. The exception was Phoro-
nis sp., whose populations were always
lowest in the microcosms because of an
artifact of the test system (larger indi-
viduals live deeper than 10 cm in the
sediment and were damaged when the
microcosms were established). It seems
that the behavior of the natural system,
and any portion of that system brought
into the laboratory, has a stochastic
component that precludes taking a few
of the species and putting the whole
back together again.
Preliminary Toxicology
Preliminary toxicity tests were con-
ducted to evaluate further the validation
criteria developed in the previous tests.
These experiments were carried out
with contaminated sediments taken
from the Elizabeth River (VA) to develop
techniques for application of a toxicant
to laboratory microcosms and field
treatments. This sediment had (parts
per thousand) concentrations of poly-
cyclic aromatic hydrocarbons. Unpol-
luted sediments from the York River and
Apalachicola estuary were used as
treatment controls. Contaminated sedi-
ments were applied to enclosures over
a twenty-four hour period to allow set-
tling of this sediment. Even with nomi-
nal toxicant concentrations, certain
problems were noted concerning the re-
sponse of the laboratory microcosms
and field treatments to the toxicants:
1. Overall, simultaneous laboratory-
field experiments require close at-
tention to the mode of application
with comprehensive chemical
analysis to evaluate equivalence of
exposure while specific objectives
of the validation process are ful-
filled.
2. Close chemical surveillance is nec-
essary concerning the distribution
of the toxicant.
3. Field treatments should be carried
out in such a way that control
areas are not contaminated.
4. Protocols for treatment should be
developed so that recognizable but
transient effects are noted without
causing persistent adverse impact
on the infaunal biota.
In summary, the nominal toxicant test
indicated that the establishment of the
microcosm treatment was the most
sensitive part of the experiment. Most
of the variation in abundance and
changes in species could be attributed
to the microcosm treatment. Through
the course of the experiment, micro-
cosms exposed to hydrocarbon-
contaminated sediment showed the
greatest degree of change. This sensi-
tivity of the laboratory microcosms to
toxic stress was documented even
though there was a considerable contri-
bution to the variance from the treat-
ments. The exposure was possibly not
as effective in the field treatments be-
cause of differences between laboratory
and field conditions in terms of water
volume and the even distribution of
contaminated sediments. This problem
may have reduced the component of
variance caused by exposure to con-
taminated sediments.
Conclusions and Recommenda-
tions
The laboratory microcosm approach
has considerable potential for evaluat-
ing microbial or macrobiological re-
sponses to natural disturbances or toxic
effects in the field, multispecies micro-
cosms have the advantage of incorpo-
rating various forms of community level
information into the experimental de-
sign; such information is not available
in single-species tests. However, be-
cause of the extremely complex rela-
tionships of such associations, a thor-
ough knowledge of the ecology of a
given site is necessary for a reasonable
application of laboratory-to-field or
field-to-field extrapolations.
Field conditions in the study areas
were characterized by short-term distur-
bances (i.e., wind and tidal currents)
and seasonal changes in the physical
environment. The microcosms followed
4
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various physical aspects of the field
habitat rather closely. However, storm-
induced disturbances were not repli-
cated and current regimes in the field
were not simulated in the laboratory.
Despite slightly increased accumulation
of silt under laboratory conditions rela-
tive to the field, no significant changes
were noted in various sediment proper-
ties among laboratory and field treat-
ments.
Biological interactions in the field
were complex and highly variable in
space and time. Physico-chemical habi-
tat changes, predation, and recruitment
influenced the macroinvertebrate as-
semblages with differential effects ex-
erted along habitat gradients and dur-
ing different seasons of the year.
Changes in the macroinvertebrate as-
semblages in the microcosms were
due, in part, to alterations during trans-
fer from field to laboratory, lack of
motile predators in the laboratory, and
altered recruitment. Such changes ap-
peared to depend on the timing of the
test and the natural assemblages of
macro!nvertebrates in the source areas
at the initiation of the microcosm.
Experiments carried out in two differ-
ent estuaries showed that the basic con-
trolling features and microcosm re-
sponse relative to the field were quite
similar. The initial establishment of the
microcosm and time-based alteration of
recruitment in the laboratory micro-
cosms were the most important ele-
ments contributing to changes in the
microcosms relative to field conditions.
The timing of the test, relative to sea-
sonal changes in recruitment, was also
an important aspect of the validation
process. Thus, correct interpretation of
microcosm results relative to field pro-
cesses depends on an understanding of
natural community processes. No sin-
gle species in the laboratory was consis-
tently representative of field conditions
either because of laboratory artifacts or
because of specific responses of indi-
vidual populations to laboratory condi-
tions.
Our experimental results demon-
strated that microcosms of soft-
sediment macroinvertebrates can be es-
tablished for short periods (5-6 weeks)
and that changes in the field popula-
tions can be either reflected in the over-
all response of the microcosms or
accounted for in terms of specific labo-
ratory artifacts. Moreover, extrapolation
of such results from one system to an-
other is possible within the range of un-
certainty that is characteristic of natural
systems. Just as extrapolation of results
from the microcosm to the field cannot,
by definition, be a direct process, so too
is extrapolation from one ecosystem to
another seriously qualified by func-
tional differences in community pro-
cesses of such systems. With adequate
qualification based on ecological knowl-
edge of the areas in question, both veri-
fication and extrapolation are feasible
within the limits of natural variation.
The strength of the validation of a
given microcosm depends on an as-
sessment of the laboratory reaction of
populations of individual species within
the uncertainty that is natural to ecolog-
ical systems. It is recommended that
validation processes be evaluated ac-
cording to criteria developed by our
studies. Further analysis is needed to
relate how well microcosms reflect the
response of natural ecosystems to toxi-
cants. The validation approach pro-
posed by our research reflects the need
to calibrate laboratory microcosms with
established processes in the field. More
work is needed to develop validation
procedures for processes in natural
communities in addition to structural
aspects of the estuarine communities
that have been emphasized in this re-
search.
Criteria for Verification Proce-
dures
The simultaneous use of replicated
multispecies microcosms (as defined in
Giesy, 1980} and field mesocosms
(Grice and Reeve, 1982) to test the vali-
dation hypothesis has led to specific ob-
servations concerning the relationships
of full-field, semi-field, and controlled
conditions. Criteria that relate the labo-
ratory and field approaches to research
of benthic estuarine associations are
given in Table 1. Physical and chemical
changes in the laboratory sea water
quality relative to field conditions are
unavoidable. Laboratory artifacts in-
clude changes in hydrostatic pressure,
and current structure, which may lead
to different sedimentation patterns. Pro-
curement, transfer, and placement of
sediments in the microcosms also
sometimes leads to severe alterations
of sediment conditions. Specific
changes in the microcosm habitat arise
from its isolation from the field and are
enhanced by surface features of the lab-
oratory enclosure. Although the effects
of laboratory conditions can be avoided
in varying degrees, duplication of field
conditions is usually precluded by the
conditions imposed on the microcosms.
The real problem is to define those as-
pects of microcosm function that can be
used to explain field conditions.
Some features of laboratory micro-
cosms are especially difficult to control.
Sudden changes of temperature or sed-
imentation in the field cannot be repli-
cated in the laboratory microcosm. At
the same time, the microcosm often
acts as a silt trap through time, thus al-
tering sediment and water column rela-
tionships relative to the field. Whereas
natural physical disturbances such as
storm effects are lacking in the labora-
tory microcosm, other features of the
sediment and water column within the
microcosm undergo a departure from
natural conditions because of the limita-
tions imposed by the size of the micro-
cosm as compared to a virtually limit-
less natural environment.
Physical disturbance of the sediments
in a given microcosm can be divided
into two primary sources of impact:
transference of sediments in the estab-
lishment of the microcosm and sam-
pling during the course of an experi-
ment. Our experiments indicated that
establishment of the microcosm and
separation from surrounding sediments
can have an immediate impact on the
macroinvertebrate assemblages in the
microcosm. Often, certain sensitive spe-
species were lost in the transfer; the
exact impact of this effect on numerical
abundance and species richness varied
according to seasonal patterns of rela-
tive abundance in the estuarine associa-
tions. Results of some experiments indi-
cated a deviation from field conditions
within time periods of 4-6 weeks. Too-
frequent (i.e., weekly) sampling of the
microcosm during such experiments
also led to alterations in the microor-
ganism and macroinvertebrate assem-
blages.
If the laboratory microcosm was iso-
lated from natural benthic assem-
blages, recruitment processes were al-
tered, as shown in results from both
research groups. Such changes can be
enhanced by handling of water prior to
entry into the microcosm. Another pos-
sible recruitment problem is isolation
from surrounding populations that
propagate through benthic transfer of
larvae rather than through plankton. Im-
migration is severely restricted. Pat-
terns of recruitment and immigration
are habitat- and time-dependent. Each
species recruitment pattern should be
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Table 1,
Factor/Condition
Criteria for Review of the Validation oflnfaunal Macroinvertebrate Microcosms with Semi-field Mesocosms and Full-Field Conditions
in Estuarine Systems
Full-field
Semi-field cage
Microcosm
Physico-chemical
Water source
Water supply
Currents
Sampling effects
Light
Sedimentation
Physical Distur-
bance
Sediment Com-
paction/pore
water
Sediment temper-
ature
Sediment pH
Substrate depth
Hydrostatic pres-
sure
No effect.
No effect.
Unaffected; variable in magnitude
and direction because of tides and
wind effects.
Damage to fauna during sampling;
slumping of sediment to fill core
holes.
Unshaded, but low light intensity
due to water depth/turbidity
Frequent resuspension.
Bioturbation by epifauna (e.g.,
crabs and fishes). Enhanced micro-
bial activity.
No effect.
No effect.
No effect.
No effect.
Variable because of tides, waves.
No effect.
Flow impeded by screen; some re-
cruits set on screen.
Slowed by screen mesh; variable
in magnitude and direction be-
cause of tide. Effects minimized by
choice of mesh and cage design.
Same as for full-field. Slumped
holes may have trapped organics,
making attractive site for larval set-
ting and immigration.
Same as full-field.
Possibly enhanced by reduced
water flow. May be reduced near
edges by scouring. No major ef-
fects noted in sediment characteris-
tics over 4-9 week periods.
Large sediment disturbances ex-
cluded, activity of smaller species
became more important. Enhanced
microbial activity.
No effect.
No effect.
No effect.
No effect.
Same as full field.
Drawn from near bottom, 50-100
m from field and semi-field site.
In-pipe setting only in last 15 m;
minimal reduction in O2; alter-
ations of larval setting.
Established by position of input
and output and by sediment boxes;
invariate once established. No true
simulation of tidal and wind-driven
currents.
Replacement of cores with azoic
sediment; migration into azoic sed-
iment led to dilution of popula-
tions. Because of scaling effect,
sampling had more of an impact
on the microcosm than under field
conditions.
Microcosm tanks varied from being
partially shaded to a general repli-
cation of light intensity in the field.
Enhanced by slow water flow in
microcosm tank. May be changed
by water intake system. Accumula-
tion of silt may have been en-
hanced beyond the rate in the field.
Certain forms of bioturbation were
enhanced because of limited area
compared to field. However, large-
scale disturbance due to storms
and tidal currents, not reproduced
in microcosms.
Compaction reduced by removal
from field and subsequent slump-
ing; probably gradual compaction
as experiment progresses. Flow of
pore water restricted, possible
changes in granulometric proper-
ties.
Temperature changes relatively
rapid, no insulation; minor differ-
ence from field.
Sedimentary processes affected pH
by shallowness of microcosm, sedi-
mentation enhancement, and
changes in compaction.
Limited escape routes, deep-
dwelling organisms eliminated.
Vertical organization of macroinver-
tebrates altered by depth restric-
tions.
Usually lower than field; less vari-
able.
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Table 1. (Continued)
Factor/Condition
Full-field
Semi-field cage
Microcosm
Biological
Larval recruitment
Predation (large,
mobile epibenthic
organisms)
Immigration
Competition
Food source
No effect.
Major impact under specific condi-
tions of salinity and at certain sea-
sons of the year.
No effect.
Interference competition may have
been important, although complex-
ity precluded generalization.
No effect.
Possibly affected by mesh of cage.
Solid substrate may have attracted
some species. Affected by mesh
size and type. No effects noted in
exclusion cages in this series of ex-
periments.
Impact reduced by exclusion of
large mobile predators.
Possible effect of screen inserted
into substrate and in water column.
Same as full field.
Possibly enhanced enrichment
from cage mesh.
Possibly affected by difference in
water source; potential change in
available recruits due to passage
through pipe; solid substrate at-
tractive for setting of some species,
selective (species-specific) mortality
in lab.
Same as semi-field.
Probably eliminated; most pelagic
immigrants were probably de-
stroyed by pumps.
Same as full-field and semi-field.
Possibly altered by seawater sys-
tem, microbial effects.
evaluated to determine the potential for
extrapolation of laboratory results to
field conditions.
Biological processes other than re-
cruitment may be altered under labora-
tory conditions. Isolation from natural
field processes disconnects microcosm
assemblages from interactions with
various types of predators. Our experi-
ments indicated that the impact of pre-
dation on field assemblages of macroin-
vertebrates was extremely complex. In
addition to gradient effects of salinity on
such impact, there were also seasonal
differences in the predator influence in
the field. During spring periods of maxi-
mal influence of predation impact in
polyhaline areas of the Apalachicola
Bay system, isolation of the microcosm
in the laboratory led to increases of
dominant populations that follow ob-
served changes in exclusion cages in
the field relative to inclusion cages and
cage controls. Such changes were asso-
ciated with altered microbial commu-
nity structure. At other times of the year
and under oligohaline conditions, no
such effects were observed. Direct and
indirect effects on natural energy rela-
tionships also occurred in the micro-
cosms. Such effects may have given
selective advantages to certain macro-
invertebrate populations. Altered pre-
dation pressure, together with unavoid-
able restrictions in the depth (and verti-
cal population distribution) of the
microcosms, may alter competitive in-
teractions that occur naturally in the
field. The difficulty of demonstrating
such complex competitive interactions
under field conditions disallows strict
generalization. Overall, simultaneous
experiments with laboratory micro-
cosms, semi-field conditions, and full-
full-field conditions indicated that bio-
logical interactions comprised an im-
portant element in the verification of the
predictive capability of microcosms to
natural conditions.
The laboratory microcosms followed
field conditions when viewed as groups
of interacting populations rather than as
sets of individual populations. Specific
community parameters, such as species
richness and diversity, and other in-
dices of multispecies associations,
when qualified by known changes
caused by laboratory artifacts, were
representative of field situations. Verifi-
cation of both microbial and macrobio-
logical assemblages was possible only
within the bounds of our knowledge of
the systems in question. Moreover, the
critical factors that determined qualifi-
cations (i.e., recruitment, predator-prey
interactions, relative species domi-
nance) were relatively similar in two en-
tirely different experimental areas.
Thus, field to field extrapolation of re-
sults is also possible when it is based on
a thorough knowledge of the subject
systems.
U. S. GOVERNMENT PRINTING OFFICE: 1985/559-111/20663
-------
R. J. Livingston is with Florida State University, Tallahassee, FL 32306, R. J. Diaz
is with the College of William and Mary. Gloucester Point, VA 23062, andD. C.
White is also with Florida State University.
T. W. Duke is the EPA Project Officer (see below).
The complete report, entitled "Field Validation of Laboratory-DerivedMult/species
A quatic Test Systems."(Order No. PB 85-214 294/AS; Cost: $ 10.00, subject to
change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Environmental Research Laboratory
U.S. Environmental Protection Agency
Gulf Breeze, FL 32561
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use $300
0000329
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