Rapid localized decline of a French Polynesian coral reef following a climatic irregularity

Abstract

Coral reefs are among the most biologically diverse and complex marine ecosystems on Earth. However, anthropogenic impacts continue to degrade coral reefs worldwide, potentially increasing the ability for localized climatic irregularities or fluctuations to cause rapid changes to habitats over limited spatial scales. Bora-Bora Island was impacted by one such irregularity between 02th and January 05, 2020, with adjacent reefs subjected to a combination of low tides, high temperature and algal bloom. Our monitoring surveys showed that after only four days of these conditions, live coral cover on some Bora-Bora reefs rapidly declined from 80 ± 7% to 20 ± 7%. In addition, the density of fishes and giant clams also decreased (i.e., respectively, from 3.6 to 6.1 individuals per m2 before climatic anomaly to 2.6 and 2.2 individuals after climatic anomaly). This study suggests that, as the mean environmental conditions continue to move towards to abiotic limits on coral reef growth and persistence, even small fluctuations above these limits could have dramatic impacts on the resilience of reef communities.