Community ecology dynamics on reefs in Fiji are dependent on soft coral density and depth

Some soft corals (order Alcyonacea) 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 to identify the relationships among benthic taxa across sites with varying degrees of soft coral dominance on the Great White Wall, Fiji, and then employed spatial point process analysis to reveal the ecological processes behind these associations. We found that depth was the dominant driver of community dynamics, and that white Nephtheidae soft corals were negatively associated with scleractinian corals and positively associated with algae due to a facilitative mutualism – possibly due to soft corals reducing grazing pressure. Our results show distinctions in reef benthos and ecological dynamics between scleractinian- and soft coral-dominated reefs. We found that diversity levels were significantly lower on soft coral than scleractinian reefs, potentially highlighting the risk of a loss in benthic diversity on reefs where soft corals replace scleractinians.