Macroarthropod Communities of Exposed Riverine Sediments Along a Low Gradient Coastal Plain River in the Southeastern U.S.A.
When the entrainment and deposition of fine sediment by flowing waters is allowed to operate unhindered, exposed riverine sediments (ERS) become distributed as a mosaic of seasonally-available, terrestrial habitats composed of bars and islands. Habitats in the form of ERS have received attention by scientists only since the late 1990s. Such attention is primarily due to threatened and endangered species that inhabit ERS in Europe. Because of the extreme vulnerability of ERS to river channelization and regulation, natural forms of these habitats have become critically imperiled throughout much of North America and Europe. This study set out to synoptically survey the macroarthropod communities of ERS on an unregulated U.S. river so as to create an initial database from which further research could be performed. I used pitfall traps to sample the surface-active macroarthropod community of ERS of the Sipsey River in Tuscaloosa County, AL, USA. Pitfall traps were deployed for 48-hour periods in 5 different ERS habitats from late June to early October of 2010 (8 sampling dates total). Although 189 taxa were identified, only four species comprised nearly 50% of the total individuals captured (>18,000): Velarifictorus micado (Gryllidae, Orthoptera), Tetragonoderus fasciatus (Carabidae, Coleoptera), Solenopsis invicta (Formicidae, Hymenoptera), and Pardosa sp. (Lycosidae, Araneae). Patterns of both abundance and community structure changed dramatically with season, with the highest levels of abundance and taxa richness occurring in August and/or September and the lowest levels occurring in early July and October. Although distance from the water explained patterns of distribution for some taxa in some ERS habitats, the overall pattern was too variable to support generalizations. Finally, invasive species comprised >50% of individuals collected, with V. micado and S. invicta together comprising 42.5% of specimens. It is thus possible that such invader species may have a significant negative impact on the community, perhaps rivaling that of anthropogenic disturbance.