Abstract Reef ecosystems face multiple threats including coral bleaching, which is primarily driven by global warming and can be intensified by local stressors. Despite evidence of global and local stressors, in situ assessments of their combined effects remain scarce for Brazilian reefs (Southwestern Atlantic), which are considered putative climate refugia, notably the subtropical reefs of São Paulo. However, these reefs are exposed to intense tourism activities. Therefore, we investigated whether local tourism exacerbates the effects of global warming by assessing Mussismilia hispida and Palythoa caribaeorum bleaching across zones with high, low, and no tourism in coastal islands during thermal stress episodes. In each zone, colonies were surveyed using photoquadrats along fixed transects over five periods. We recorded numerous activities in high tourism zones throughout all monitoring periods, particularly boat anchoring in reef areas. Despite enduring severe anomalies of 10.1 °C-weeks, in the Fourth Global Bleaching Event context, bleaching remained below 43%, with negligible mortality. However, bleaching was exacerbated by local stressors, with estimated incidence rates 22 and 16.5 units higher for P. caribaeorum and M. hispida in high tourism zones, reaching up to 59%, while minimal rates occurred in the no tourism zone (≤ 10% for P. caribaeorum ; ≤ 17% for M. hispida ). Our findings demonstrate that local pressures amplified bleaching across all monitored islands, despite their potential as future climate refugia, and that environmental protection can effectively enhance the resistance of coral assemblages in these marginal rocky reefs, thereby reducing long-term bleaching consequences.
Mariano et al. (2026) studied this question.