Invertebrate communities of forested limesink wetlands in southwest Georgia, USA: Habitat use and influence of extended inundation

Limesink wetlands are a common aquatic habitat in southwest Georgia, USA. These wetlands are non-alluvial, occupying shallow depressions formed from dissolution of limestone bedrock and collapse of surface sands. They are seasonally inundated, with a typical hydroperiod extending from late February to early July. Little is known about factors influencing invertebrate community structure in limesink wetlands. Recently, it has been suggested that regular inundation and drying are important influences on community structure in some seasonal wetlands. We had an opportunity to examine this hypothesis in 3 forested limesink wetlands. Quantitative samples of invertebrates were taken monthly on benthic and wood surfaces from March 1994 through July 1995. This included a period of unusually heavy precipitation, summer and autumn of 1994, when the wetlands would normally be dry. Immediately following inundation, benthic samples were dominated by amphipods (Crangonyx sp.), isopods (Caecidotea sp.), cladocerans, and copepods. Maximum total densities (1000-4000 individuals per m(2)) were observed within 3 months of inundation. During summer and autumn, densities decreased (< 500 individuals per m(2)), and the benthos was dominated by larval chironomids. Wood surfaces were dominated by chironomids, with greatest densities (1000-3000 individuals per m(2)) observed in summer and autumn. Although not quantified, freshwater sponge became very abundant on wood surfaces during autumn. During the following spring (1995), invertebrate densities on sediments remained low, and few amphipods, isopods, cladocerans, or copepods were collected. Chironomids remained very abundant on wood. Our results suggest that extended inundation is a disturbance to some elements of wetland invertebrate communities. Extended inundation may cause short-term reductions in populations by eliminating summer refugia (amphipoda, isopoda) or by altering environmental cues necessary for the completion of life cycles (cladocerans, copepods).