Size Variation and Recruitment of Macoma sp. in the Southern Chukchi Sea and Possible Implications of Seasonal Ocean Acidification in the Pacific Arctic

Recent sea ice retreat and seawater warming in the Pacific Arctic are physical changes that can have direct impacts on benthic macrofaunal community composition and biomass. We used recent van Veen grab collections of the tellinid bivalves Macoma calcarea and M. moesta in July 2014 (n=84) and 2015 (n= 284), as well as historical length/weight data from the past twenty years, to follow changes in both size and recruitment of this genus at a highly productive station north of Bering Strait (UTN2; 67.05 N, 168.73 W). These bivalves are common benthic prey items for migrating walrus, bearded seals and diving seaducks, and this location is known to be a productive and biologically significant foraging hotspot. Since size and availability of prey items can affect the success of feeding bouts by benthivores, following the recruitment and size distributions of the benthic food base allows for a better understanding of potential feeding behaviors and shifts in response to biological changes.

Clam lengths in 2014 ranged from 14 mm to 55 mm, with an average length of 25.8 mm, and clam lengths in 2015 ranged from 15 mm to 50 mm, with an average size of 21.3 mm. New recruitment is surmised based upon size trend changes within the 20-year data set. In addition, ongoing seasonal ocean acidification may be affecting shell growth and respiration rates, based upon results from on-going laboratory experiments using these Macoma sp.clams. This additional influence has the potential for altering size classes and faunal composition available to the foraging benthivores.