Marine heatwaves (MHWs) are increasingly intense and frequent, causing significant stress to coastal foundation species such as macroalgae, seagrass, and corals. A global study analyzed the impacts of MHWs on these species across 85 marine ecoregions, revealing that MHWs have led to major population changes, with the proportion of negative responses increasing over time. The study found that MHWs have a stronger impact on species near their warm range edges, with some ecoregions showing little to no response. Key factors influencing the impacts include the intensity, duration, and temperature of MHWs, as well as the species' geographic range. The study highlights that the loss of foundation species can lead to ecosystem collapse, affecting biodiversity, ecological function, and ecosystem services. The results suggest that many coastal ecosystems are losing foundation species, which could have far-reaching ecological and socioeconomic consequences. The study also identified that some species show resilience to MHWs, and that responses vary across ecoregions. The findings emphasize the need for better understanding of how MHWs affect species and ecosystems, and for developing management strategies to mitigate their impacts. The study used a combination of long-term ecological data and MHW metrics to assess the impacts of MHWs on foundation species, revealing that strong MHWs are more likely to cause significant damage. The study also found that responses to MHWs vary depending on the species and ecoregion, with some species showing positive responses under certain conditions. The study underscores the importance of understanding the complex interactions between MHWs and foundation species to develop effective management and adaptation strategies.Marine heatwaves (MHWs) are increasingly intense and frequent, causing significant stress to coastal foundation species such as macroalgae, seagrass, and corals. A global study analyzed the impacts of MHWs on these species across 85 marine ecoregions, revealing that MHWs have led to major population changes, with the proportion of negative responses increasing over time. The study found that MHWs have a stronger impact on species near their warm range edges, with some ecoregions showing little to no response. Key factors influencing the impacts include the intensity, duration, and temperature of MHWs, as well as the species' geographic range. The study highlights that the loss of foundation species can lead to ecosystem collapse, affecting biodiversity, ecological function, and ecosystem services. The results suggest that many coastal ecosystems are losing foundation species, which could have far-reaching ecological and socioeconomic consequences. The study also identified that some species show resilience to MHWs, and that responses vary across ecoregions. The findings emphasize the need for better understanding of how MHWs affect species and ecosystems, and for developing management strategies to mitigate their impacts. The study used a combination of long-term ecological data and MHW metrics to assess the impacts of MHWs on foundation species, revealing that strong MHWs are more likely to cause significant damage. The study also found that responses to MHWs vary depending on the species and ecoregion, with some species showing positive responses under certain conditions. The study underscores the importance of understanding the complex interactions between MHWs and foundation species to develop effective management and adaptation strategies.