EVALUATING MACROINVERTEBRATE POPULATION AND COMMUNITY-LEVEL EFFECTS IN OUTDOOR MICROCOSMS - USE OF IN-SITU BIOASSAYS AND MULTIVARIATE-ANALYSIS

Evaluating toxicant effects on aquatic communities is difficult due to the ecological complexity at higher levels of organization. Two metho ds were assessed to improve the understanding of effects on macroinver tebrate communities in aquatic model ecosystems. First, in situ bioass ay population effects were used to interpret effects at a higher organ ization level. Second, canonical discriminant analysis was used to inv estigate effects on community structure. In situ bioassays were conduc ted on six occasions in 17-m(3) microcosms treated with copper sulfate . Macroinvertebrates occurring naturally in the microcosms were monito red. Epibenthic in situ bioassays were conducted using Caenis sp. (Eph emeroptera) and Hyalella azteca (Amphipoda) and a water column bioassa y was conducted using Notonectidae (Hemiptera). Survival and growth we re assessed after 3 d. Effects of copper on both Notonectidae and Caen is were observed following application. However, the final Caenis epib enthic bioassays indicated that potential for recovery and survival wa s greater than or equal to 95%. Potential for recovery was less distin ct in the water column bioassays. Copper effects also occurred on epib enthic macroinvertebrate populations and communities. Only four taxa, including Caenis, distinguished community differences among copper tre atments soon after application. Later, communities showed similarities to the pretreatment bioassay. However, actual recovery was less appar ent than the potential for recovery indicated by the bioassays, and co mmunity differences due to Caenis persisted.