Abundance, biomass and caloric content of Chukchi Sea bivalves and influence on Pacific walrus (Odobenus rosmarus divergens) abundance and distribution in the northeastern Chukchi Sea
MetadataShow full item record
The northeastern Chukchi Sea is a shallow subarctic shelf ecosystem that supports a significant benthic infaunal community. Bivalves are one of the dominant benthic taxa in this region, and represent a vital food resource for consumers such as Pacific walrus (Odobenus rosmarus divergens). The biomass, abundance and species composition of these bivalve communities not only reflect local patterns of productivity, but have the potential to affect upper trophic level consumers through bottom-up processes. Ten dominant bivalve taxa were collected over four cruises in the northeastern Chukchi Sea from 2009-2013 to establish baseline parameters in size frequency distributions, abundance, biomass and caloric content and to quantify their influence on the distribution of Pacific walrus. Pooled size-frequency distributions across all years showed strongly right-skewed distributions for most taxa, with a few showing evidence of a bimodal distribution. Calorimetric measurements revealed significant differences in caloric density between taxa (p-value < 0.001), and whole animal wet weight was a reliable predictor of caloric content. Abundance and biomass were largely dominated by calorie-dense, deposit-feeding species, including Macoma spp., Ennucula tenuis, Nuculana spp. and Yoldia spp.. Hotspot analysis revealed areas of high abundance, biomass and calories centered on and to the southeast of Hanna Shoal. Pacific walrus abundance from June through October was generally greatest in areas of high bivalve abundance and biomass. ANOVA analysis showed significant differences in mean caloric values between areas with and without walrus present (student’s t-test, p-value < 0.001), as well as between areas with low and high densities of walrus in the pooled annual dataset and in each individual month except October. The dominant bivalve taxa in this study were high-calorie deposit feeders which preferentially consume food sources that are likely to be affected by shifting sea ice dynamics, such as benthic microalgae and sea ice algae. As such, shifting sea ice dynamics have the potential to dramatically alter bivalve communities in the northeastern Chukchi Sea that may have profound implications for upper trophic levels.