Influence of soft coral density and depth on benthic communities on Fiji's Rainbow Reef

Abstract

Some soft corals have the potential to increase in prevalence on tropical coral reefs as the severity of anthropogenic climate change increases. While soft corals are therefore an increasingly important component of reef ecosystems, little is known about their ecological role on coral reefs and their influence on community dynamics and diversity. We used Bayesian network inference (BNI) to identify the associations among benthic taxa across sites with varying degrees of soft coral dominance on Fiji's Rainbow Reef, and then employed spatial point process analysis (SPPA) to reveal the ecological processes behind these associations. We found that depth was a dominant driver of community dynamics, and that white Nephtheidae soft corals were negatively associated with scleractinian corals and positively associated with algal proliferation—possibly owing to soft corals reducing grazing pressure. Our results show distinctions in reef benthos and ecological dynamics between scleractinian and soft coral-dominated components of the Rainbow Reef. We found that diversity levels were significantly lower on soft coral-dominated quadrats relative to scleractinian-dominated quadrats, potentially highlighting the reduction in benthic diversity when Nephtheidae soft corals dominate reef walls.