Climate Change and Local Impacts Threaten Brazilian Coral Reefs

Brazilian reefs are hypothesized as potential climate-change refugia due to the lower occurrence of coral bleaching events and mortality rates than other reefs regions worldwide. This hypothesis is called Brazilian Reef Refugia Hypothesis (BRRH). In this book chapter, we review the chronic and acute stressors that are currently affecting these unique reefs and communities, including long-term warming, marine heatwaves (MHWs), acidification, sea-level rise, mismanaged touristic and industrial activities, higher nutrient inputs, increased plastic pollution, human-caused disasters (e.g., oil spills and mining), overfishing, and invasive species such as lionfish (Pterois spp.) and sun corals (Tubastraea spp). The results show the uneven incidence and frequency of stressors, which characterizes a regional wide-variation in human pressures, vulnerability and reef resistance. These stressors are impacting these reefs as cumulative and synergistic pressures and, consequently, undermining their potential to provide long-term refugia contradicting BRRH. Overall, there was an increase of the sea surface temperature and MHWs at all reef regions in the last 39 years, including the year 2024 as the worst heat stress ever recorded. The effects of warming and MHWs, the main stressors, have been most significant in low-latitude reefs, where the sea temperature has been heated twice as much as the eastern Brazilian reefs (0.2 °C versus 0.1 °C per decade). Moreover, the frequency of MHWs have increased more in equatorial reefs than in higher latitude reefs (15–20 °S). Despite being hypothesized by BRRH as more resistant than the Caribbean and Indo-Pacific reefs, the Southwestern Atlantic reefs present a large number of phase-shift events and indicators of reef decline (e.g., decreasing richness, biomass, and loss of architectural complexity) which indicates significant degradation in the supply of geo-ecological functions such as reef framework production and sediment generation, the maintenance of reef habitat complexity and reef growth potential. The disproportionate distribution of rare fish species and decreased fish biomass also reveals a higher vulnerability to human impacts. Overall, all the Southwestern Atlantic reefs are threatened by a plethora of human pressures until the end of this century, have limited potential to provide climate-change refugia, and need urgent attention to reduce and mitigate impacts at local and global scale.