Thirty years of coral bleaching in the Southwestern Atlantic Ocean: a historical assessment based on degree heating week indices

Abstract Three decades have passed since the first documented coral bleaching event in the Southwestern Atlantic Ocean. Rising sea surface temperatures continue to threaten coral conservation. Due to particular characteristics of Southwestern Atlantic coral communities, the influence of heat stress on bleaching events remains a challenge. Here, we review reports of coral bleaching over the past 30 yrs and their relationship to sea surface temperature anomalies. Coral bleaching reports were compiled from 1992 to 2022 and compared with bleaching predictions based on degree heating week (DHW) indices. Our results indicate that about 15% of the analyzed bleaching events were reported during periods of high DHW conditions. In contrast, 80% of these events occurred after 2010, coinciding with an average increase of 3 $$^{\circ }$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts> <mml:mrow/> <mml:mrow/> <mml:mo>∘</mml:mo> </mml:mmultiscripts> </mml:math> C week in DHW values. These results support the expected increase in the influence of heat stress as one of the main causes of coral bleaching in recent years. In addition to a potential bias in bleaching reporting, corals near the coast between 3 $$^{\circ }$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts> <mml:mrow/> <mml:mrow/> <mml:mo>∘</mml:mo> </mml:mmultiscripts> </mml:math> S–9 $$^{\circ }$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts> <mml:mrow/> <mml:mrow/> <mml:mo>∘</mml:mo> </mml:mmultiscripts> </mml:math> S and 15 $$^{\circ }$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts> <mml:mrow/> <mml:mrow/> <mml:mo>∘</mml:mo> </mml:mmultiscripts> </mml:math> S–18 $$^{\circ }$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mmultiscripts> <mml:mrow/> <mml:mrow/> <mml:mo>∘</mml:mo> </mml:mmultiscripts> </mml:math> S appear to be historically most affected by heat stress events. Although no clear improvement in bleaching prediction performance was found by incorporating local SST variability into the DHW calculation, we suggest that extensive monitoring efforts could lead to a better understanding of this relationship under future climate change scenarios.