A global analysis of coral bleaching patterns in association with mangrove environments under global warming

Abstract

Marine heatwaves caused by global warming are progressively degrading coral reefs worldwide via the process of coral bleaching – the expulsion of photosynthetic endosymbionts. However, coral bleaching is not spatially homogeneous, but varies across environmental gradients in association with local conditions and taxonomic composition. Emerging evidence suggests that mangrove habitats are recurrent ‘'microenvironments' for reef corals, providing key biogeochemical services believed to influence their resilience, and housing co‐tolerant coral taxa. This close association between coral reefs and mangroves has led to the hypothesis that the extent of coral bleaching is reduced by the proximity of reef building corals to mangroves. Here, we present the first global‐scale test addressing this hypothesis. Using Bayesian generalised linear mixed effect modelling, we show that coral bleaching tends to increase under higher thermal stress when corals are further away from mangroves. When comparing conditional effects, corals furthest away from mangroves also show the highest levels of bleaching, suggesting a phenomenon of reduced bleaching for corals residing closer to mangroves under thermal stress. The drivers of this pattern may be numerous, but most likely include the presence of co‐tolerant coral species which are known to be associated with mangroves. Future research should focus on disentangling the mechanisms underlying these coral bleaching patterns in association with mangroves, specifically focusing on in‐situ environmental and taxonomic data collection. These endeavours will most likely require high‐resolution analyses of coral reefs at more local‐scales. Ultimately, our findings add to the ever‐growing importance of mangroves for near‐shore coral reef environments, and suggest a potentially important benefit for coral reefs associated with mangroves in the Anthropocene.