Different responses of massive and branching corals to a major heatwave at the largest and richest reef complex in South Atlantic

In 2019, a major coral bleaching event affected reefs worldwide, including marginal reefs within the Abrolhos Bank (16°40′–19°40′S, 39°10′–37°20′W), the largest and richest coral reefs in the South Atlantic. Between March and May 2019, this area was affected by the strongest heatwave since 1985. The health trajectories of the branching hydrocoral Millepora alcicornis and the endemic reef-building coral Mussismilia braziliensis were recorded during this thermal stress event. The degree heating week value reached its historical maximum (DHW 19.65), causing bleaching in 100% of Millepora alcicornis and 80% of Mussismilia braziliensis colonies. Bleached Millepora alcicornis were rapidly covered by cyanobacteria, followed by algal turfs and calcareous algae, leading to 90% mortality. Conversely, 90% of Mussismilia braziliensis colonies recovered to a healthy state after bleaching. The high post-bleaching recovery capacity and resistance to mortality of this massive reef-building coral suggests these marginal reefs can be resilient to thermal stress events, despite losing structural complexity due to high mortality of branching and less abundant hydrocorals.