Differential vulnerability to climate change yields novel deep-reef communities

Abstract

The effects of climate-driven ocean change on reef habitat-forming species are diverse1,2 and can be deleterious to the structure and functioning of seafloor communities3–5. Although responses of shallow coral- or seaweed-based reef communities to environmental changes are a focus of ecological research in the coastal zone1,4–6, the ecology of habitat-forming organisms on deeper mesophotic reefs remains poorly known. These reefs are typically highly biodiverse7,8 and productive as a result of massive nutrient recycling9. Based on seafloor imagery obtained from an autonomous underwater vehicle8, we related change in community composition on deep reefs (30–90 m) across a latitudinal gradient (25–45° S) in southeastern Australia to high-resolution environmental and oceanographic data, and predicted future changes using downscaled climate change projections for the 2060s10–12. This region is recognized as a global hotspot for ocean warming13. The models show an overall tropicalization trend in these deep temperate reef communities, but different functional groups associate differentially to environmental drivers and display a diversity of responses to projected ocean change. We predict the emergence of novel deep-reef assemblages by the 2060s that have no counterpart on reefs today, which is likely to underpin shifts in biodiversity and ecosystem functioning. Deep reefs and their inhabitants are diverse, but environmental change, in particular warming, will cause these reefs found along southeastern Australia to tropicalize with different responses across functional groups, resulting in novel communities by the 2060s.