ABSTRACT
Marine heatwaves, which are becoming more prolonged, frequent and intense under climate change, now pose a significant threat to ocean species and ecosystems. Long-term observational studies that encompass these events can offer critical insights into how continued climate change will alter marine life across scales, from physiological effects on individuals to altered species interactions to ecosystem-scale processes. Between 2014 and 2016, the Northeast Pacific experienced what, to this day, remains the longest recorded marine heatwave globally, triggering a wide range of ecological responses. We conducted a systematic review of observational studies from this heatwave and synthesised the documented ecological impacts. We identified 331 relevant English-language primary reports (from 2256 records recovered), including both peer-reviewed and grey literature. In total, 240 species were found outside of their typical geographical ranges during the heatwave, with many of them (n = 101) found further north than ever before. The prolonged heatwave also drove kelp forest declines, reorganised plankton communities, altered offshore oceanographic productivity and impacted seagrass meadows and intertidal habitats. Cascading indirect effects of the heatwave were also far-reaching, driving record seabird die-offs, unusual mortality events in humpback whales, reduced abundance and nutritional quality of forage fish, the near extinction of a key rocky shore predator, Pycnopodia helianthoides, and closures of multiple fisheries, driven by changes in species interactions, disease proliferation or habitat loss. This comprehensive analysis highlights the need to better understand and mitigate the impacts of marine heatwaves, emphasising the urgency to strengthen marine ecosystem resilience in a warming world.
