Coral mass mortalities in the Chagos Archipelago over 40 years: Regional species and assemblage extinctions and indications of positive feedbacks.

The global decline of reef corals has been driven largely by several marine heatwaves. This has greatly reduced coral cover but has reduced coral diversity also. While there is a lack of data in most locations to detect coral species losses, reefs of the Chagos Archipelago, central Indian Ocean, have long term monitoring data extending back to the late 1970s. Severe declines in cover have occurred since the 1970s, with regional extinctions of some species and key species assemblages. There is a severe decline in coral settlement, along with a substantial loss of habitat quality which has reduced the habitat available for settlement. This is a clear precursor to positive feedback. Regional species extinctions here occur mainly when total coral cover is <10% of pre-warming levels. Climate models predict more frequent and more severe marine heatwaves, and even if this ecosystem recovers it will contain fewer species.

One size does not fit all: the emerging frontier in large-scale marine conservation.

On the 20th anniversary of the Convention on Biological Diversity, a network of very large marine protected areas (the Big Ocean network) has emerged as a key strategy in the move to arrest marine decline and conserve some of the last remaining relatively undisturbed marine areas on the globe. Here we outline the ecological, economic and policy benefits of very large-scale MPAs and show their disproportionate value to global marine conservation targets. In particular we point out that very large-scale MPAs are a critical component of reaching the Aichi targets of protecting 10% of global marine habitats by 2020, because in addition to encompassing entire ecosystems, they will bring forward the expected date of achievement by nearly three decades (2025 as opposed to 2054). While the need for small MPAs remains critical, large MPAs will complement and enhance these conservation efforts. Big Ocean sites currently contain more than 80% of managed area in the sea, and provide our best hope for arresting the global decline in marine biodiversity.

One-third of reef-building corals face elevated extinction risk from climate change and local impacts.

The conservation status of 845 zooxanthellate reef-building coral species was assessed by using International Union for Conservation of Nature Red List Criteria. Of the 704 species that could be assigned conservation status, 32.8% are in categories with elevated risk of extinction. Declines in abundance are associated with bleaching and diseases driven by elevated sea surface temperatures, with extinction risk further exacerbated by local-scale anthropogenic disturbances. The proportion of corals threatened with extinction has increased dramatically in recent decades and exceeds that of most terrestrial groups. The Caribbean has the largest proportion of corals in high extinction risk categories, whereas the Coral Triangle (western Pacific) has the highest proportion of species in all categories of elevated extinction risk. Our results emphasize the widespread plight of coral reefs and the urgent need to enact conservation measures.