A comprehensive coastal seabird survey maps out the front lines of ecological change on the western Antarctic Peninsula

Seabirds along the western Antarctic Peninsula are known to be shifting in abundance and distribution in response to changing sea ice and prey distributions, but the spatial extent of these changes has remained an open question because survey efforts have focused on the more easily accessed northern coastline. We used a yacht-based field expedition (January 5–21, 2013) to complete the first comprehensive penguin (Pygoscelis spp.) and blue-eyed shag (Phalacrocorax [atriceps] bransfieldensis) population survey of the Graham and Loubet Coasts of the western Antarctic Peninsula since the mid-1980s. Our surveys document a sharp transition zone at the northern boundary of Marguerite Bay; north of this boundary zone, we confirm widespread declines in Adélie penguins and increasing populations of gentoo penguins, but south of this zone we find Adélie populations that have remained stable or increased in abundance since the previous surveys by Poncet and Poncet (Br Antarct Surv Bull 77:109–129, 1987). Marguerite Bay has long been known as a predator “hotspot,” but our findings suggest that Marguerite Bay has actually been improving for marine predators for at least several decades. Marguerite Bay, which has fundamentally different ocean dynamics than in areas just outside Marguerite Bay, has maintained persistent phytoplankton blooms over the past decade even as summer sea ice extent, which can inhibit access to breeding areas, has declined. This provides further support for the hypothesis that ocean productivity and sea ice dynamics are critical factors regulating Adélie penguin abundance in the region and that Marguerite Bay is now at the front lines of ecological change in this region.