Temperature extremes in the Gulf of Maine: A synthesis of marine heatwaves, cold-spells, and ecological impacts

Easton R White , Camyrn J Ragland, Jannine D Chamorro , Selina L Cheng, Valerie Eddington, Danielle Fradet, Kaila J Frazer, Miguel de Jesus Gomez Garcia, Ariel Greiner, Natalie Lord, Andrew R Villeneuve, Amanda White, Ryan Wisdom

Long-term environmental change has been altering ecosystem function and phenology globally. Short-term temperature pulses, often called extreme temperature events, can accelerate impacts of long-term change on ecosystems by forcing rapid changes in food webs, triggering range shifts, and disrupting reproductive cycles. Marine ecosystems at the confluence of large global currents are particularly vulnerable to extreme temperature events because small shifts in currents can trigger rapid local change. The Gulf of Maine, located at the confluence of the Labrador Current and the Gulf Stream, is one such marine ecosystem. The Gulf of Maine has experienced rapid warming in recent decades, punctuated by frequent extreme temperature events which have impacted productive fisheries and diverse ecosystems in the region. Yet, synthesis work has not quantified changes in extreme temperature events over time or the implications for Gulf of Maine ecosystems. From 1993 to 2025, we observed a 3% yearly increase in marine heatwave events with a 4% yearly decrease in marine cold-spells, but trends varied spatially across the Gulf of Maine. To assess how these events are impacting Gulf of Maine ecosystems, we conducted a formal literature review. Here, we identified 12 papers (from a search of 539 that met our initial criteria) that focused on extreme temperature events affecting ecosystems in the Gulf of Maine; this dearth of papers highlighted the need for more work in the region. Across marine ecosystems, we noted the direct physiological impacts of extreme events, as well as the cascading effects these events cause by enabling the spread of disease, altering food webs, and disrupting fisheries. We also reviewed how extreme events affect coastal human communities and how this might change in the future with emerging stressors and human migration. Lastly, we pointed out research gaps, especially in relation to designing management plans that account for extreme events.