Sea urchins (diadematids) promote coral recovery via recruitment on Taiwanese reefs

Abstract

Coral reefs are of global concern in the face of increasing anthropogenic disturbance. Much research has focused on the negative factors associated with coral reef decline, but few have documented the positive factors in relation to recovering coral reefs. Here, we report a positive quantitative association between sea urchins (diadematids), coral recruitment and coral recovery, recorded along Taiwanese coral reefs. We monitored coral cover change, juvenile coral density, herbivore density (fishes, sea urchins, gastropods) and macroalgal cover, along three reefs between 2012 and 2015. Multivariable regression analyses revealed that sea urchin (diadematids) density was the primary (positive) driver, explaining 74% of variation in coral cover change and 89% in coral juvenile density among sites and years. The relationship between sea urchin density and coral juvenile density was especially evident for four common coral genera: Acropora, Dipsastraea, Pocillopora and Porites. These results suggest that diadematid urchins enhance coral recovery on these reefs by promoting the recruitment of corals. The density of juvenile corals was also found to explain 67% of variation in coral cover change, highlighting the potential use of coral juvenile density as a proxy for coral recovery potential in coral resilience studies.