The impacts of marine heatwaves on coastal ecosystems in a rapidly warming world

Climatic extremes are becoming increasingly common against a background trend of global warming. In the oceans, the frequency and duration of marine heatwaves (MHWs)—periods of anomalously warm water—have increased significantly over the past century, with wide-ranging impacts on ecosystems and coastal societies.  Our understanding of MHW patterns, drivers and impacts has expanded rapidly in recent years, with MHWs emerging as pervasive drivers of ecosystem change. We quantified trends and physical attributes of MHWs heatwaves globally, and examined their biological impacts from individuals to ecosystems. The physical attributes of prominent recent MHWs varied considerably, but all had deleterious impacts across a range of biological processes and taxa, including critical foundation species (e.g. corals, seagrasses and kelps). Certain regions may be particularly vulnerable to MHW intensification, due to the co-existence of high levels of biodiversity or concurrent human impacts. An examination of how MHWs influence ecosystem service provision revealed significant socioeconomic impacts, and also highlighted opportunities and examples of successful management interventions. MHWs are now recognised as forceful agents of disturbance with the potential to restructure entire ecosystems and disrupt the provision of ecosystem services. Improved forecasting combined with a wider range of adaptation measures will facilitate management decisions and help guide conservation efforts, which will be integral for future-proofing marine biodiversity and ecosystems in a warmer world.