Ecosystems mediate climate impacts on northern hemisphere seabirds

Ecosystem structure and biophysical processes mediate biological responses to climate changes, but few studies have examined impacts of this dynamic among upper trophic levels. We investigated ecosystem differences in how diverse seabird populations across the northern hemisphere have responded to changes in regional mixed layer temperature and water column stratification. Using 138 time series of breeding productivity over the past half-century, we show that seabird reproductive productivity has declined in the Arctic and North Atlantic but not in the Pacific during a period of ubiquitous mixed layer warming and regionally-variable stratification trends. Models of breeding productivity and ocean drivers show that seabird responses to climate change vary by ecosystem. Additionally, ecosystems in which seabirds exhibit detectibly declining productivity tend to have lower overall diet diversity across seabird species. These findings emphasize the importance of ecosystem processes and structure in determining the vulnerability of marine predators to climate change. Diet diversity across northern hemisphere ecosystems affects seabird responses to climate change, with breeding productivity declining in the Arctic and North Atlantic but not in the Pacific from 1993 to 2019, based on 138 time series of breeding success and linear mixed effects models.