Effects of common carp (Cyprinus carpio) on macrophytes and invertebrate communities in a shallow lake

1. We performed two field experiments using different cage sizes to determine the direct and indirect effects of carp on macrophytes and invertebrate community composition in a shallow lake. 2. The presence of carp produced a significant decrease in macrophyte abundance, changes in species composition and decreased abundance and diversity of invertebrates in small (2.5 x 2.5 x 2.0 m) cages. In large exclosures (15 x 5 m), only macrophyte stem length was significantly affected by carp. 3. There was considerable variation in the macrophyte and invertebrate responses to carp on different sides of the lake in the large exclosures, suggesting that wind and wave action are also important variables affecting macrophyte growth and persistence. 4. The data suggest that carp can significantly affect species abundance and diversity of macrophytes and some macroinvertebrates.