Drivers of Coral Reef Benthic Changes and Implications on Ecosystem Functioning and Services

Increasing anthropogenic stressors will likely result in many coral reefs undergoing compositional and functional benthic changes, including towards non-hard coral-dominated communities. The decline of reef-building species and the increase of alternative (i.e., non-reef-building) organisms profoundly affect the functioning of coral reefs and the services provided, but this remains poorly understood, especially for non-algal alternative communities. Here, we propose a standardised framework to study coral reef benthic changes and review the knowledge on coral reef shifts and their implications on coral reef functioning and service provisioning using this framework, which contains the five following elements: (1) contextual information, (2) drivers and triggers, (3) feedback mechanisms, (4) changes in ecosystem functions and (5) effects on ecosystem services. We highlight the importance of biotic and abiotic interactions in determining the likelihood, magnitude and direction of community changes, showing that similar drivers and triggers can lead to multiple alternative communities, depending on the environmental biotic and abiotic conditions. We stress the need to build a robust and comparable database in different ecoregions that includes both biotic information about the community and its environmental characteristics over a relevant timescale. Finally, we stress the need for understanding not only the causes (i.e., drivers and triggers) behind the changes but also the processes behind the persistence of the novel communities (i.e., feedback mechanisms), as well as their broader socio-ecological relevance (e.g., impact on ecosystem functions and services). Addressing all these knowledge shortfalls is vital to increase the prediction power of coral reef benthic changes, understand their persistence and design effective restoration measures to facilitate coral recovery.