Temporal and spatial distribution of macrobenthos communities and their responses to environmental factors in Lake Taihu

Study of the responses of macrobenthos communities structure to environmental gradients is a hot topic in community ecology and environmental assessment. Macrobenthos communities are not only influenced by environmental gradients, but also caused by life-cycle, hydrologic, water temperature, feeding resources or habit heterogeneity especially for the seasonal changes of structure and composition. The seasonal change may mask the effect introduced by environmental gradients. At the same time, macrobenthos has fixed habits because the long life history and low athletic abilities, and the distribution of macrobenthos community demonstrate habit difference caused by human activities and natural difference. Research about macrobenthos community spatial and temporal variability has an important means for biological assessment. To explore the distribution and seasonal change of macrobenthos communities and their responses to environmental factors in Lake Taihu, 12 metrics based on abundance, diversity, functional feeding group, dominance and tolerance value were chosen to represent macrobenthos community. We seasonally investigated macroinvertebrate assemblages and local environment at 18 sites in Lake Taihu from the winter of 2010 to the autumn of 2012. A total of 42 macrobenthos species were collected, including 15 species of molluscs, 10 species of annelids, and 17 species of arthropods. Indicator Value Analysis indicated (ISA) that Corbicula fluminea, Limnodrilus hoffmeisteri and Tubificidae sp. were the indicator species of the whole lake each with a indicator value of 84.21. In the North Bays, L. hoffmeisteri, C. fluminea and Polychaeta sp. with the indicator values of 57.54, 51.23 and 48.92 respectively were the indicator species. In the East Bays, Nephthys sp., Branchiura sowerbyi and Bellamya aeruginosa were the indicator species with indicator values of 48.01, 37.53 and 37.26 respectively. In the Open Lake Area, C. fluminea, Nephthys sp. and Cythura sp. were the indicator species with indicator value of 30.79, 25.61 and 23.28 respectively According to Generalized Linear Mixed Models, variations of macrobenthos community metrics within regions and seasons were of significant difference, the seasonal changes of macrobenthos community metrics exist throughout the sampling years. Distance-based linear models (DistLM) were used to examine the relationships between macrobenthos community metrics and environmental factors. The key environmental variables related to macrobenthos community were total nitrogen (TN), total phosphorus (TP) and ammonia nitrogen (NH4+) in North Bays, pH, total nitrogen (TN) and water temperature (T) in East Bays, and dissolved oxygen (DO) and water temperature (T) in Open Lake Area. In addition, abundance-based macrobenthos metrics best responded to the environmental factors. The result of distance-based linear models indicated that North Bays and East Bays were better explained by environmental factors relative to Open Lake. For macrobenthic community metrics, metrics based on abundance were better explained by environmental factors. The forward selection suggested that TN, TP and NH4+ were the main environmental factors affecting macrobenthic community in North Bays. PH, TN and water temperature were the main environmental factors affecting macrobenthic community in East Bays. DO and water temperature were the main environmental factors affecting macrobenthic community in Open Lake.