The role large marine herbivores play in coral reef resiliency and recovery in Palmyra Atoll

Coral reefs are essential underwater ecosystems. However, due to detrimental anthropogenic factors such as overfishing, coral reef health have declined. An important contributor that helps maintain healthy coral reefs are marine herbivores who remove algae that competes with corals for space on the benthos. In this study, we investigate the role large marine herbivores (>50 cm) play in coral recruitment and reef recovery. The Caselle Lab set up 12 herbivore exclusion cages at a recovering reef at Palmyra Atoll National Wildlife Refuge. Each cage includes 2 settlement tile sandwiches that measure the rates of coral recruitment. After analyzing the tiles collected in 2019 and 2020, we found that the number of coral recruits in treatments where herbivores are excluded dramatically decreases. We found evidence that large herbivores prevent the establishment of macroalgae, which may impact coral growth and survival. However, we did not find a strong effect on coral settlement when only large herbivores were excluded.