Listening to global warming: assessment of the impact of coral bleaching and marine protection measures in Polynesia through passive acoustic monitoring

Among the different disturbances affecting coral reefs, climate change is expected to become the major cause of their degradation towards this century. In coral reefs, anomalously high sea temperatures are linked to coral bleaching events. Mass bleaching events alter the ecological process of coral reefs while marine protected areas (MPAs) can increase the resilience of coral reef communities to natural disturbances, playing a role in sheltering biodiversity from climate-related impacts and in the recovery of corals from massive bleaching events. In Moorea Island (French Polynesia), two bleaching events occurred between 2015 and 2021. The aims of this study are to compare the soundscape of the external slope of Moorea Island within and outside MPAs in 2021 to access the presence or the absence of a protection effect on acoustic data and to compare them to data sampled in 2015 to access both temporal and protection effects, in relation with the benthic cover and the fish species present. MPAs have a greater fish species richness and coral cover than surrounding areas (contrary to what was observed in 2015, showing a possible reserve effect) while their low-frequency power spectral density was lower. Between 2015 and 2021, coral cover decreased by 10%. When comparing 2015 and 2021 soundscapes, nocturnal high-frequency biophony were louder on the sites from the east coast, i.e. the only sites with an increase of coral cover between 2015 and 2021. This link between high power spectral density values and coral cover between 2015 and 2021 confirm the efficacity of passive acoustic for long term monitoring.