Macroinvertebrate Abundance and Distribution in Hydrilla and Ceratophyllum Habitats

Assessment of aquatic macroinvertebrate abundance and species composition can be useful for understanding aquatic system structure, water quality variation, and the forage base available to fishes. Vegetation-dwelling invertebrates are important food organisms for juvenile and adult fishes, particularly in lakes with few benthic organisms. Epiphytic invertebrate densities are typically tied to the quality and quantity of habitat available, which can be strongly influenced by the species composition of the resident macrophyte community.  Many lentic habitats in the southern U.S. have been invaded by exotic hydrilla Hydrilla verticillata, but the consequences of these invasions to native macroinvertebrate communities have not been determined. The goal of this study was to assess the impacts of hydrilla infestations on the littoral macroinvertebrate community in the Atchafalaya River Basin located in south central Louisiana.  Our objectives were to determine the abundance and community composition of hydrilla-dwelling aquatic macroinvertebrates, evaluate the effects of macrophyte-induced reductions in water quality on macroinvertebrate densities, and compare macroinvertebrate densities between hydrilla and native coontail (Ceratophylum demersum) beds. Collections were made with a trap that consisted of a 60 x 45 cm suitcase constructed of 0.5-cm thick angle aluminum with 600-µ stainless steel mesh walls. Preliminary results indicate that water quality not only affects macroinvertebrate abundance, but also influences macroinvertebrate diversity in these macrophyte beds.