Climate Change Drives Bathymetric Shifts in Taxonomic and Trait Diversity of Deep-Sea Benthic Communities.

Climate-induced changes in environmental gradients can cause shifts in ranges of organisms and community composition, with concomitant effects on ecosystem functions. Throughout geological time, deeper depths have been highlighted as refugia for biodiversity and ecosystem functions under a warming climate. Although the deep ocean provides several important ecosystem services, contemporary research on climate effects at the community and ecosystem levels has been limited to the upper 200 m of the water column. As a result, our knowledge of climate-induced impacts on the functions of deep-sea ecosystems is scarce. In this study, we examined climate-induced changes in deep-sea communities at a climate-change hotspot, the Gulf of Maine and adjacent continental slope in the Northwest Atlantic. We focused on deep-water coral communities, which are among the most diverse in the deep sea. Using a joint species distribution model, we projected and examined community composition, taxonomic diversity, and trait diversity of deep-water coral communities under two climate scenarios for the end of the century (2100). We found extensive shifts of suitable habitat for several coral genera from 500-1000 to 1500-2000 m, mostly attributed to warming in the upper 1000 m. This led to substantial reduction (30%-60%) in the existing taxonomic and functional richness at the upper continental slope, alongside gains in richness (10%-15%) at the lower continental slope and bathyal zone. Our study is the first to report extensive shifts in biodiversity from mesopelagic to bathyal depths, which will inevitably cause redistribution of ecosystem functions and services. These results showcase that climate change impacts at the ecosystem level are not restricted to shallow depths and highlight that further knowledge of them is essential for efficient conservation, planning, and management.