A five-year study was carried out to determine the feasibility of using multispecies microcosms of infaunal macroinvertebrates to predict the responses of estuarine systems to toxic substances. Criteria were developed to evaluate the field validation of laboratory microcosms. Experiments carried out in the Apalachicola Bay system in Florida demonstrated that infaunal macroinvertebrates can be established for short periods (five to six weeks) and that the microcosms can be used to simulate certain features of natural field assemblages.

Water quality in the microcosms essentially paralleled that in the field, although variation of certain water features and sediment characteristics was noted. These laboratory artifacts were apparently caused by the isolation of the microcosms from natural phenomena of the estuarine environment that were not replicable in the laboratory. Physical habitat features and biological responses in the study area were extremely complex and highly variable in space and time. Factors such as water and sediment quality, predator-prey relationships, recruitment, and dominance relationships among infaunal populations, influenced the community structure of benthic organisms in the laboratory and the field. The relative influence of physical and biological factors varied considerably between habitats and through time. Consequently, the extent to which the laboratory microcosms paralleled field conditions depended to a considerable degree on the time of testing and dominance/recruitment features of the system in the source area. Species richness in the laboratory microcosms appeared to be a good indicator of field conditions. Multispecies tests have certain advantages over single-species tests in terms of the expanded scope of evaluation. However, results from such experiments should be interpreted within established limits of natural environmental variation. Each microcosm should undergo a thorough calibration with field conditions to qualify the influence of laboratory artifacts and to identify the potential problems associated with isolation from key controlling factors in the field.