Amphipod species behavioral adaptations to the absence of open water

Biological surveys of fauna in the Mid-Atlantic Piedmont and Coastal Plain document significant distributions of various amphipod species populations. These amphipods occupy diverse habitats and have evolved highly specialized traits specific to their niche environment. Little is understood about amphipod species habitat preferences—particularly how some species survive the seasonal changes of ephemeral habitats, with drastic water level fluctuations. Three amphipod species with populations in Washington, DC include: Gammarus minus, Crangonyx shoemakeri and Stygobromus tenuis potomacus. These species are most commonly found in separate habitats, each species having developed its own distinct behavioral adaptations to succeed. This study tests the survival of these species in the laboratory when open surface water is removed, calculating survival rates and recording observed behaviors. Crangonyx shoemakeri and Stygobromus tenuis potomacus commonly found in seeps, springs and hypotelminorheic habitats, successfully avoid desiccation after air exposure. After correcting for expected deaths, no additional deaths were recorded without surface water for both these species. Gammarus minus are ill-suited to combat this stress and die-off relatively quickly under these conditions. After correcting for expected deaths, approximately 25% of the Gammarus minus in tests without open surface water died. This difference in survival along with corresponding behavioral adaptations broadens knowledge of mechanisms allowing success of Crangonyx shoemakeri, and Stygobromus tenuis potomacus in ephemeral environments and reveals their competitive advantage against other species.