Arctic bivalve dead-shell assemblages as high temporal- and spatial- resolution archives of ecological regime change in response to climate change

Abstract

A 15-year time-series of data on benthic community response to rapid climate change at a biomass ‘hotspot’ in the northern Bering Sea, Alaska, provides an exceptional opportunity to evaluate naturally occurring molluscan dead-shell assemblages as ecological archives. We find that, at five middle-shelf stations censused annually from 2000 to 2014, dead-shell assemblages collected in 2014 are dominated by obligate deposit-feeding Nuculanidae bivalves as opposed to the other families in that guild or the facultative deposit-feeding Tellinidae that dominate the most recent living bivalve assemblages, thus correctly detecting the location and direction of known ecological changes. However, live–dead contrast is significant where the bivalve biomass and abundance has declined over time, and muted where bivalve abundances, and therefore shell input, increased, underscoring the general danger of assuming constant shell input. We also find that proportional abundance-based measures are best suited for detecting benthic response to climate change. Combined with preliminary results from shell age-dating, these results indicate that dead-shell assemblages provide a short-lived but compositionally faithful ecological memory well-suited for detecting recent site- and habitat-level ecological change under cold-water conditions. With marine regime change suspected to now be underway throughout the Arctic, molluscan dead-shell assemblages should become an integral part of efforts to detect transitioning regions.