Marine heatwaves (MHWs) are increasingly frequent and intense, posing significant threats to global biodiversity and ecosystem services. This study quantifies trends in MHWs across all ocean basins and examines their biological impacts. MHWs, defined as periods when daily sea-surface temperatures exceed a local seasonal threshold for at least five consecutive days, have increased significantly over the past century. These events have caused widespread mortality, species range shifts, and community reconfiguration, particularly in regions with high biodiversity and temperature sensitivity. The study highlights that MHWs are likely to intensify with anthropogenic climate change, leading to ecosystem restructuring and disruption of ecological goods and services. The research identifies regions vulnerable to MHWs, including the Pacific, Atlantic, and Indian Oceans, where high biodiversity and temperature-sensitive species coexist with non-climatic human impacts. MHWs have been linked to negative ecological impacts on various taxa, with sessile organisms like corals and seagrasses being particularly affected. The study also shows that MHWs have significant correlations with decreased ecological health of foundation species such as corals, seagrasses, and kelp. These events have severe consequences for marine ecosystems, including loss of biogenic habitat, disrupted nutrient cycles, and shifts in commercial fisheries. The study conducted a meta-analysis of ecological responses to eight prominent MHW events, revealing negative effects on biota across different taxa and response variables. The most significant impacts were observed on sessile organisms, with corals and birds being particularly vulnerable. The analysis also found that populations near the warm range edge of species' distributions were more negatively impacted by MHWs. The study emphasizes the need for managing and mitigating the effects of MHWs on ecosystem services, as they are becoming more frequent and prolonged, with record-breaking events observed in most ocean basins. The findings underscore the importance of addressing MHWs in marine conservation and management strategies to maintain the integrity of valuable marine ecosystems. The study provides a comprehensive understanding of the impacts of MHWs on marine biodiversity and ecosystem services, highlighting the urgent need for adaptive management practices to mitigate the effects of climate change on marine environments.Marine heatwaves (MHWs) are increasingly frequent and intense, posing significant threats to global biodiversity and ecosystem services. This study quantifies trends in MHWs across all ocean basins and examines their biological impacts. MHWs, defined as periods when daily sea-surface temperatures exceed a local seasonal threshold for at least five consecutive days, have increased significantly over the past century. These events have caused widespread mortality, species range shifts, and community reconfiguration, particularly in regions with high biodiversity and temperature sensitivity. The study highlights that MHWs are likely to intensify with anthropogenic climate change, leading to ecosystem restructuring and disruption of ecological goods and services. The research identifies regions vulnerable to MHWs, including the Pacific, Atlantic, and Indian Oceans, where high biodiversity and temperature-sensitive species coexist with non-climatic human impacts. MHWs have been linked to negative ecological impacts on various taxa, with sessile organisms like corals and seagrasses being particularly affected. The study also shows that MHWs have significant correlations with decreased ecological health of foundation species such as corals, seagrasses, and kelp. These events have severe consequences for marine ecosystems, including loss of biogenic habitat, disrupted nutrient cycles, and shifts in commercial fisheries. The study conducted a meta-analysis of ecological responses to eight prominent MHW events, revealing negative effects on biota across different taxa and response variables. The most significant impacts were observed on sessile organisms, with corals and birds being particularly vulnerable. The analysis also found that populations near the warm range edge of species' distributions were more negatively impacted by MHWs. The study emphasizes the need for managing and mitigating the effects of MHWs on ecosystem services, as they are becoming more frequent and prolonged, with record-breaking events observed in most ocean basins. The findings underscore the importance of addressing MHWs in marine conservation and management strategies to maintain the integrity of valuable marine ecosystems. The study provides a comprehensive understanding of the impacts of MHWs on marine biodiversity and ecosystem services, highlighting the urgent need for adaptive management practices to mitigate the effects of climate change on marine environments.