Impact of spatiotemporal variability in phytoplankton size structure on benthic macrofaunal distribution in the Pacific Arctic

The size structure of the phytoplankton community strongly affects energy flow through food webs; hence, monitoring the spatial and temporal dynamics of phytoplankton size structure is crucial to evaluate variability in marine ecosystems. In this study, the spatiotemporal changes in phytoplankton size structure and their impact on benthic macrofaunal distribution were examined in the Pacific Arctic as part of the international Distributed Biological Observatory effort. The exponent of the chlorophyll-a(Chia) size distribution (hereafter, CSD slope), which is an index of synoptic size structure of a phytoplankton community, was estimated based on spectral shape of the phytoplankton absorption coefficient using satellite ocean color data. The CSD slope during the post-bloom period was significantly correlated with sediment Chia concentration, suggesting that the amount of organic carbon input to the seafloor was strongly related to surface phytoplankton size structure after the spring bloom. Average macrofaunal biomass in the Pacific Arctic was persistently high (> 20 g C m(-2)) throughout 2000-2013 in the regional hotspots, and the biomass-based latitudinal centroid of macrofaunal habitat in the region shifted significantly (p < 0.05) northward. This northward shift is likely driven by a spatiotemporal change in phytoplankton size structure during the post-bloom period. Our results suggest that bottom-up forcing by the phytoplankton community affected the distribution of benthic macrofauna. We conclude that the remote estimate of phytoplankton size structure largely contributes to advancing our knowledge of ecosystem changes observed in the Pacific Arctic marine ecosystem.