Effects of structural marsh management and salinity on sediments, hydrology, invertebrates, and waterbirds in marsh ponds during winter on the Gulf Coast Chenier Plain

Compositions of wintering waterbird communities are dependent upon food accessibility (via water depth), biomasses and sizes of their invertebrate prey, which in turn are influenced by the hydrology and sediments of wetland habitats. The hydrology and sediments of marsh ponds on the Gulf Coast Chenier Plain probably are affected by structural marsh management (levees, water control structures and impoundments; SMM) and salinity; therefore, SMM and salinity ultimately may affect wintering waterbird communities.; Accordingly, I measured sediment and hydrologic variables, biomasses and sizes of common aquatic invertebrates, and densities of common wintering waterbird species in ponds of impounded freshwater (IF), impounded oligohaline (IO), impounded mesohaline (IM), and unimpounded mesohaline (UM) marshes during winters 1997--1998 to 1999--2000 on Rockefeller State Wildlife Refuge, near Grand Chenier, Louisiana.; SMM affected sediment and hydrologic variables, which negatively affected biomasses of Nematoda and secondarily increased those of Ostracoda. However, few waterbird species possess the capacity to capture these small prey; consequently, I predicted that avian species that consume invertebrates would not be among those differentiating waterbird communities between ponds of IM and UM marshes. Comparisons of waterbird densities provided inconsistent results with this prediction because some shorebird and waterfowl species that feed heavily on invertebrates were those that primarily differentiated waterbird communities between ponds of IM and UM marshes.; My comparison of IF, IO, and IM marsh ponds indicated that, except for salinity, they differed little in sediment and hydrologic variables. Accordingly, these marshes only differed in biomass of Oligochaeta; consequently, I predicted that avian species that consume invertebrates would not be among those differentiating waterbird communities among ponds of IF, IO, and IM marshes. Accordingly, their waterbird communities primarily differed in densities of waterbird species that feed on vegetation.; In conclusion, some waterbird species exclusively used ponds of UM marshes rather than ponds of IM marshes, and most species had highest densities in IF marshes when water depth favored those that maximized their densities. Consequently, my results suggest that marsh managers should focus on the preservation of UM and IF marshes for the conservation of wintering waterbird populations on the Gulf Coast Chenier Plain.