Aquatic macroinvertebrate food resources for birds in a Texas coastal marsh

Abstract

Wetlands of the San Bernard National Wildlife Refuge (SBNWR) were sampled to investigate environmental factors which influence aquatic macroinvertebrate standing crop and diversity. Sampling occurred monthly between February and July of 1987 within wetlands delineated as Fresh, Impounded, Intermediate, and Saline. Study sites within these wetlands were stratified into open and emergent marsh based upon prevalence of emergent vegetation cover. Aquatic insects were the most abundant invertebrate group within SBNWR wetlands. Chironomids were the dominant aquatic insect f family and were most abundant within Intermediate open marsh. Corixids were the second most abundant aquatic insect f family and were most prevalent within Saline open marsh. Crustaceans were the second most abundant group, with Isopods and Amphipods being the dominants. Fresh emergent marsh contained the greatest abundance of Crustaceans. Gastropods and Oligochaetes were most abundant in Fresh marsh and Impounded open marsh. Emergent strata of the Impounded, Intermediate, and Saline wetlands had a greater diversity of aquatic macroinvertebrates than their corresponding open-marsh stratum. Aquatic macroinvertebrate standing crop peaked between March and April in all wetlands. Declines after this period were attributed to wetland drawdown, maturation of larval stages and perhaps perdition. Peak standing crop coincided with mottled duck nesting and early brood rearing. Fresh-open and emergent, Impounded open, Intermediate-open and emergent, and Saline-open marsh contained high numbers and biomass of preferred waterfowl invertebrate foods. Wetland management should be aimed at maintaining the existing conditions at these sites because they provide ideal food resources for waterbirds.