Patterns in fish assemblages from coastal wetland and beach habitats in Green Bay, Lake Michigan: a multivariate analysis of abiotic and biotic forcing factors

From May to September in 1990 and 1991, 24 coastal wetland and beach sites in Green Bay, Lake Michigan, were sampled to investigate abiotic and biotic factors influencing fish assemblages; half the sites were modified by human developments, and half were relatively undeveloped. The greatest assemblage differences were observed among regions, but there also were strong differences among assemblages from different habitats. Degree of development had less of an effect on site differences, although assemblages at undeveloped wetlands were unique, and those from developed and undeveloped sites in the upper bay were relatively distinct. The most influential abiotic factors were turbidity, reflecting the trophic gradient in the bay, and a suite of variables associated with macrophyte coverage and diversity, which were critical components of nursery habitats for the primarily immature fishes we captured. The volatile and unpredictable nature of shoreline habitats in the Great Lakes apparently precluded competition and predation from having a strong organizing role. This study demonstrates that undeveloped wetlands are a valuable and intensely utilized fish habitat, particulartly as nursery areas, that should receive special consideration in ecosystem management plans for the Great Lakes.