Changes in abundance and biomass of the bivalve Macoma calcarea in the northern Bering Sea and the southeastern Chukchi Sea from 1998 to 2014, tracked through dynamic factor analysis models

We used dynamic factor analysis (DFA) to track underlying trends in the abundance (number m(-2)) and biomass (g C m(-2)) of a common bivalve, Macoma calcarea, at eleven stations in the northern Bering and Chukchi Seas, as part of the Distributed Biological Observatory (DBO) sampling effort. Five of the stations are located in the northern Bering Sea (DBO1 - SLIP stations) and the other six stations are located in the southeastern Chukchi Sea (DBO3 - UTN stations). M. calcarea abundance and biomass were analyzed from 1998 to 2014 as part of a 25 + year benthic community dataset. Results from the DFA indicate that there are two abundance trends (one increasing and one decreasing, depending on station location) for M. calcarea in the DBO1 region. Biomass data for M. calcarea in this region also indicates simultaneous increasing and decreasing trends, depending on location. In the DBO3 region, there are also both increasing and decreasing abundance trends for M. calcarea depending on location. Furthermore, DFA of biomass data in the DBO3 region indicates that M. calcarea biomass has three underlying trends among stations (one increasing, a second trend that decreases and then increases, and third that is relatively stable through time). Model results indicate that certain surface sediment characteristics (chlorophyll-a inventories, total organic carbon, and percent >= 5 phi grain size) as well as bottom water temperature are correlated with abundance and biomass of M. calcarea in these two regions. Overall, we conclude that M. calcarea abundance and biomass declined in the DBO1 region, with some spatial complexities, which is apparent principally as a northward shift of M. calcarea abundance. Since this area is a critical winter foraging habitat for the world population of a threatened diving sea duck, the spectacled eider (Somarteria fischeri), the decline and northward shift in prey is potentially significant for management of the species. By comparison, abundance of M. calcarea in the DBO3 region exhibited a southward shift in abundance away from station UTN5 and towards UTN2, suggesting that hydrographic influences on sediment composition and food supply may be key drivers for this species.