Deteriorating Predation Refugia as a Barrier to the Recovery of Keystone Species Diadema antillarum

Abstract

Diadema antillarum is a keystone species that is crucial for maintaining the health and stability of Caribbean coral reefs. After a mass mortality event decades ago, their population abundance has not seen any improvements. Hard coral cover is important for maintaining coral reef structural complexity, which offers predation refugia for D. antillarum. Recently, hard coral cover has rapidly declined across the Caribbean coral reefs, causing flattening and diminishing structural complexity. This study aims to examine how deteriorating predation refugia inhibits juvenile D. antillarum survival by comparing refuge quality and D. antillarum densities between study sites Utila, which exhibits weak recovery of D. antillarum, and Banco Capiro, which shows a unique population recovery. This study found a significant lack of juvenile survival into adulthood in Utila when compared to Banco Capiro. These differences in survival were associated with significantly different refuge quality between the sites, indicating that refuge quality is a driver of study site population differences. Interestingly, predation pressures did not differ significantly between the sites. Finally, this study’s results show that while juvenile D. antillarum population levels were not significantly determined by refuge quality, the transition from juvenile to adult was. This finding suggests that quality of predation refugia offered by coral reefs has a role in determining juvenile survival. Restoring refuge quality could serve to facilitate D. antillarum population recovery.