Seabirds in the Arctic and North Atlantic struggle to raise chicks as the ocean becomes warmer and more stratified. Meanwhile, birds in the Pacific are still doing better. What explains this difference? The answer lies in the ecosystems.
An Atlantic puffin at Røst returns to its chick with mackerel – an unusual prey species for this site, which may signal a change in the food web due to climate change. Photo © Tycho Anker-Nilssen
Why do climate impacts vary?
Climate change is warming the oceans, affecting everything from plankton to top predators like seabirds. But the effect is not the same everywhere. Researchers behind a study published in Communications Earth & Environment wanted to find out why some seabird populations are hit hard while others appear more resilient.
"We know the ocean is warming, but we’ve lacked knowledge about how this affects seabirds in different marine regions", says Tycho Anker-Nilssen, one of the authors behind the study.
Long time series and diet data
The researchers analysed 138 time series of breeding success data for 39 seabird species across the Northern Hemisphere – from the Arctic to Hawaii – and linked these data to changes in ocean temperature and water stratification between 1993 and 2020. They also examined how varied the birds’ diets are in different ecosystems.
Species diversity matters
The picture is clear: in the Arctic and North Atlantic, seabirds show declining breeding success. These areas have both warmer surface waters and stronger stratification, which can reduce nutrient availability. Birds in the Pacific and Hawaii, however, show no clear decline despite rising temperatures.
"When the ocean becomes more stratified, nutrients stay at depth. That means reduced productivity of food for fish – and thereby less food for the birds", Anker-Nilssen explains.
Another key finding was that seabirds in the Arctic and North Atlantic had more uniform diets than the populations in the Pacific. This suggests that ecosystems with low diet diversity – where birds have few alternative prey – are the most vulnerable.
Species diversity is crucial
The study shows that climate effects are not just about temperature, but about the structure of the entire ecosystem. Where birds have a broad range of food resources, they can easier adapt to changes. Where diets are narrow, the consequences are greater.
"This is a wake-up call. Marine management must consider the entire food web, not just individual species", says Anker-Nilssen.
"If we want to help seabirds, we also need to safeguard diversity in the ocean."
Read the article: Ecosystems mediate climate impacts on northern hemisphere seabirds