UNIQUE INFORMATION CONTRIBUTED BY MULTISPECIES SYSTEMS - EXAMPLES FROM THE STANDARDIZED AQUATIC MICROCOSM

Single-species toxicity tests are inadequate to predict the effects of chemicals in ecological communities although they provide data on the relative toxicity of different chemicals, and on the relative sensiti vity of different organisms. Only multispecies studies can provide dem onstrations of: (1) indirect trophic-level effects, including increase d abundances of species via increased food supply through reduced comp etition or reduced predation; (2) compensatory shifts within a trophic level; (3) responses to chemicals within the context of seasonal patt erns that modify water chemistry and birth and death rates of populati ons; (4) chemical transformations by some organisms having effects on other organisms; and (5) persistence of parent and transformation prod ucts. Multispecies laboratory studies, such as the Standardized Aquati c Microcosm, have much to offer, with advantages of statistical power, speed of analyses, demonstrated reproducibility among laboratories, a nd modest expense (compared to held studies). The use of a chemically defined sediment facilitates the potential extraction of parent and tr ansformation products by minimizing the problem of unextractable resid ues. The absence of fish prevents the potential elimination of zooplan kton if fish predation exceeds production. Standardized Aquatic Microc osms also offer a wealth of analytical tools, including rapid statisti cal analyses, a mathematical model (MICMOD), and artificial intelligen ce methodologies.