Widespread diversity deficits of coral reef sharks and rays

Coral reef ecosystems are facing increasing threats from human activities, such as fishing, water pollution, and climate change.

Among the vulnerable species affected are sharks and rays, which play important roles as predators and prey in coral reef food chains and nutrient cycles.

Recent studies indicate that overfishing has pushed sharks towards functional extinction on many reefs, with surveys reporting their absence on nearly 20% of surveyed reefs.

This research aimed to assess the extent of species loss in elasmobranch (sharks and rays) communities by studying 391 coral reefs across 67 nations and territories. Baited remote underwater video stations were used to record species richness, composition, and relative abundance.

The study identified 104 elasmobranch species and estimated the depletion of nine key resident species. Results showed that the depletion of reef sharks ranged from 0% to 100% across individual reefs, with an average depletion of 62.8%.

Clustering analysis revealed distinct groups of reefs with varying levels of shark depletion and increasing dominance of ray species.

This study provides valuable insights into the global extinction risk of elasmobranchs and the factors influencing their assemblage structure, highlighting the importance of preserving predator diversity for the functioning of coral reef ecosystems.