Spatial variation of benthic invertebrates at the whole-ecosystem scale in a large eutrophic lake

Abstract

The spatial distribution of benthic invertebrates is fundamental to the ecology of lakes and has implications for higher trophic levels and ecosystem processes. We conducted a lake-wide study of the spatial variation of benthic invertebrates in Lake Winnebago, Wisconsin (USA) with emphasis on the chironomid community. We asked: 1) What is the extent of spatial variation in benthic invertebrate community structure and abundance among and within major lake zones in the lake? 2) What factors are correlated with spatial variation of benthic invertebrates at multiple scales? 3) How has the chironomid community and the abundance of Chironomus varied temporally at the multidecadal scale in the lake? We collected benthic invertebrates from the profundal (33 sampling locations), offshore reef (17), and littoral (15) zones in August 2013. Profundal locations were sampled again in August 2014. Habitat variables, including water depth and temperature, Secchi depth, and benthic organic matter were measured with the goal of investigating potential causes of variation in the biota. The highest mean invertebrate densities occurred in the offshore reef and littoral zones (13,987 and 10,638 individuals [ind]/m2, respectively), relative to the profundal zone (2103 ind/m2). Zebra mussels were the numerically dominant taxon in both the littoral and offshore reef zones, whereas chironomids were the most abundant macroinvertebrates in the profundal. Large differences in chironomid community composition occurred among the 3 major zones. Within the profundal zone, the pattern of spatial variation in total chironomid abundance differed between the 2013 and 2014 sampling events. Local factors (e.g., sediment characteristics) and stochastic factors (e.g., wind and current speed) probably interact to influence the spatial distribution of chironomid taxa between and within zones in large shallow lakes, such as Lake Winnebago.