Coastal wetland insect communities along a trophic gradient in Green Bay, Lake Michigan

Insects of Great Lakes coastal wetlands have received Little attention in s pire of their importance in food webs and sensitivity to anthropogenic stre ssors. We characterized insect communities from four coastal wetlands that spanned the length of a trophic gradient in Green Bay during spring and sum mer of 1995. We sampled flying insects using sticky traps in dense emergent , sparse emergent, and open water-submergent vegetation zones within each w etland and estimated numerical abundance, biomass (mg dry weight) and taxon omic composition. We found that insect abundance and biomass were distribut ed differently among vegetation zones within wetlands along the gradient du ring both spring and summer. insect abundance was highest at oligotrophic P ortage Marsh during spring and lowest in wetlands toward the lower (souther n), eutrophic end of the bay. Biomass did not differ consistently along the trophic gradient but increased with increasing emergent vegetation cover i n 3 of 4 wetlands during both seasons. Ordination revealed distinct gradien ts in community structure on both regional (i.e., upper, middle, and lower Green Bay) and local (vegetation zones within wetlands) scales. Wetlands so rted in order of trophic status during both seasons, primarily due to abund ant small Chironomidae, such as trophic-sensitive Heterotrissocladius chang i, in middle and upper bay wetlands. Chironomidae also were a dominant comp onent of open water-submergent assemblages in all wetlands. Lower bay wetla nds were characterized by fewer but larger Chironomidae (e.g., Chironomus s pp.), as well as Ceratopogonidae, Calliphoridae, and Ephydridae, which were most abundant in stands of emergent vegetation. Our results suggest that e utrophy in the lower bay may contribute to relatively poor foraging conditi ons for insectivorous fish and young waterfowl during spring, and they demo nstrate the utility of using insect communities to assess environmental deg radation, such as excessive nutrient loading, in coastal wetlands of the Gr eat Lakes.