Influences of size structure and post-bloom supply of phytoplankton on body size variations in a common Pacific Arctic bivalve (Macoma calcarea)

Abstract

The substantial loss of Arctic sea ice will alter marine ecosystems in many ways. Recent studies have reported a distributional shift in benthic macrofaunal biomass in the Pacific Arctic, likely caused by changes in food availability for benthic organisms. Here, we assessed the influence of differences in post-bloom supply of phytoplankton to the sediment on the growth of a common Pacific Arctic bivalve (Macoma calcarea) based on field and satellite observations, and feeding experiments. Among the sampling stations examined, the spatial distribution of M. calcarea body size showed clear variations and was associated with phytoplankton size structure during the post-bloom period. In addition, our feeding experiment exposing M. calcarea to different feeding treatments suggest that the continuous settlement of fresh phytoplankton is more important for the bivalve's growth than the total amount of phytoplankton settlement. This could explain the significant linkage between M. calcarea body size and phytoplankton size structure during the post-bloom period, because the larger phytoplankton represent an influx of fresh phytoplankton to the sediment and hereby support better growth and/or longevity of bivalves. Our study provides novel insights into a variety of processes related to the growth of M. calcarea and its relationship with the phytoplankton community.