Half of Atlantic reef-building corals at elevated risk of extinction due to climate change and other threats

Abstract

Atlantic reef-building corals and coral reefs continue to experience extensive decline due to increased stressors related to climate change, disease, pollution, and numerous anthropogenic threats. To understand the impact of ocean warming and reef loss on the estimated extinction risk of shallow water Atlantic reef-building scleractinians and milleporids, all 85 valid species were reassessed under the IUCN Red List Categories and Criteria, updating the previous Red List assessment of Atlantic corals published in 2008. For the present assessment, individual species declines were estimated based on the modeled coral cover loss (1989-2019) and projected onset of annual severe bleaching events (2020-2050) across the Atlantic. Species traits were used to scale species' relative vulnerability to the modeled cover declines and forecasted bleaching events. The updated assessments place 45.88%-54.12% of Atlantic shallow water corals at an elevated extinction risk compared to the previous assessments conducted in 2008 (15.19%-40.51%). However, coral cover loss estimates indicate an improvement in reef coverage compared to the historic time-series used for the 2008 assessments. Based on this, we infer that, although remaining dangerously high, the rate of Atlantic reef coral cover decline has surprisingly slowed in recent decades. However, based on modeled projections of sea-surface temperature that predict the onset of annual severe bleaching events within the next 30 years, we listed 26 (out of 85) species as Critically Endangered in the IUCN Red List. Each of these species had previously been listed under a lower threatened category and this result alone highlights the severe threat future bleaching events pose to coral survival and the reef ecosystems they support.

Fig 1. IUCN red list of threatened species categories and criteria.

Fig 2. Proportion of Atlantic reef-building corals in IUCN red List categories by family.

Number of species in parentheses. Red List categories are distinguished by color; Critically Endangered (CR) red, Endangered (EN) orange, Vulnerable (VU) yellow, Near Threatened (NT) green, Least Concern (LC) dark green, and Data Deficient (DD) gray.

Fig 3. Distribution of threatened Atlantic reef-building corals by marine ecoregions.

Atlantic reef-building corals as (a) the number of species and (b) proportion of species threatened divided by marine ecoregions.

Fig 4. Estimated change in coral cover by marine ecoregions.

Range in estimated change in coral cover by ecoregions of the Atlantic Ocean as modeled by the Global Coral Reef Monitoring Network for the T1 time-series (1978 – 2008; blue) and for the T2 time-series (1989 – 2019; red). Estimated changes in coral coverage include the median estimate (50%) as well as the 80% and the 20% uncertainty bounds or confidence intervals available for each ecoregion. Data points are not plotted for Eastern Brazil & Trindade & Martim Vaz Islands due to extremely high estimated changes in coral cover.