Interannual health status stability of the reef-building coral Montastraea cavernosa in a Southwestern Atlantic marginal reef

Abstract

Severe coral mortality after bleaching is well documented in the Indo-Pacific and Caribbean, but in the marginal Southwestern Atlantic, corals often exhibit lower post-bleaching mortality and high recovery following temperature anomalies. Understanding how these corals respond to environmental fluctuations can provide insights into their resilience against thermal stress. A seven-year assessment of the dominant reef-building coral Montastraea cavernosa was conducted in the oceanic archipelago of Fernando de Noronha, Southwestern Atlantic (3.86°S 32°42W), using a colony-based approach. We quantified healthy and bleached coral areas, colony area covered by algae, colony's border interactions with benthic organisms, and adjacent benthic cover during austral spring and relate eventual patterns with environmental drivers. Between 2013 and 2019, analyses of 43 colonies across three sites (totaling 167 observations) revealed that they largely remained healthy, with over 70 % of the area exhibiting a vivid dark color, and only small bleached areas (less than 1 %), despite a moderate-strong heatwave in 2018–2019. The adjacent algal cover fluctuated and was positively related to more turbid waters (higher sedimentation and organic matter input), but the monitored colonies were more contacted than expected by chance by algal turfs, a benthic group that does not impose a major competitive threat to corals. While it is unclear if corals bleached between sampling periods, the results suggest that reefs dominated by M. cavernosa may resist/recover thermal stress events, differing from the responses observed in the Indo-Pacific and Caribbean, highlighting the importance of including these marginal reefs in global assessments of coral responses to climate change.