Marine heatwaves, including well-documented events along the west coast of North America (2013–2016) and east coast of Australia (2015–2016, 2016–2017 and 2020), drive abrupt shifts in community composition that may persist for years (very high confidence), with associated biodiversity loss (very high confidence), collapse of regional fisheries and aquaculture (high confidence) and reduced capacity of habitat-forming species to protect shorelines