BENTHIC AMPHIPOD COMMUNITY IN THE NORTHERN BERING SEA - ANALYSIS OF POTENTIAL STRUCTURING MECHANISMS

The age class structure of ampeliscid populations is determined largely by competition for space. Population densities of the various ampeliscid species are regulated by a balance between required carbon flux rates to the seafloor, predation rates, competition for space and reproductive potential. The largest taxa require high organic matter input and low predation rates to mature and reproduce. Reductions in organic matter flux favor smaller taxa. Low predation rates favor larger taxa, which can out-compete the smaller taxa for available space. High predation rates favor smaller taxa, which have a higher reproductive rate and are therefore more effective colonizers. The above factors can explain the relative concentrations of Ampelisca macrocephala, Ampelisca birulai and Byblis spp., the most abundant ampeliscids in the northern Bering Sea. Elevated predation losses to gray whales will depress the density of the large-sized A. macrocephala populations and increase the density of the smallest species, A. birulai. Global warming should elevate ampeliscid food requirements, and may also lead to elevated predation rates, both selecting for smaller species.