The same pathway to the Weddell Sea birdlife, after 65 years: similarities in the species composition, richness and abundances

Abstract

As part of a multi-year study of top predators in Antarctica, we conducted a seabird shipbased survey on board Almirante Irizar icebreaker in the Weddell Sea to the Filchner Ice Shelf in the austral summer 2020. We carried out 10-minute counts along 1843 km during 125 hours of observation. We analyzed the species distributions and the relationships with the ice cover. We registered 15 species of which four represented more than 85% of the total abundance: Antarctic petrel Thalassoica antarctica (43.9%), snow petrel Pagodroma nivea (16.3%), Arctic tern Sterna paradisaea (15.2%) and emperor penguin Aptenodytes forsteri (10.1%). Species distribution and its relationship with ice cover were analyzed statistically. The ice cover concentration was estimated by using satellite images. We compared our results with the first ship-based bird survey conducted up to the Filchner Ice Shelf in the austral summer 1955/56 to analyze possible changes in the bird community over time. Out of 13 recorded species in the 1955/56 cruise, 11 were present in this study with similar abundance proportions. In both cruises, the bird community consisted of a group of non-numerous species associated with icefree waters and another group of very numerous species associated with high concentrations on ice cover. The similarities between the two cruises, spaced 65 years apart, suggest a temporal persistence of the bird community of the central and the southern Weddell Sea that could be explained by the dynamics of the ice cover and the presence of reproductive colonies within the study site. The current environmental warming is alarming in this bird community because more than 85% of all its individuals belong to four species strongly dependent on ice cover.

The response of trophic interaction networks to multiple stressors in a marine latitudinal gradient of the Southern Hemisphere

“…Rescued sea ice can significantly affect their post-and future breeding foraging success (Wege et al 2021). In addition, the Antarctic petrel Thalassoica antarctica, which is one of the most abundant seabirds in the area, is a sea ice dependent forager and breeder (Orgeira et al 2021); therefore the loss of this habitat will degrade its foraging success and reproductive output over time. The snow petrel Pagodroma nivea also relies heavily on sea ice for foraging and its colonies in the Weddell Sea may be affected.…”

“…The Arctic tern Sterna paradisaea spends the summer in the Weddell Sea exploiting krill swarms under receding ice edges, then declines in ice cover may reduce prey availability and quality of molting habitats. Continued warming is thus expected to gradually erode the abundance and distribution of these 'primary species' that dominate the avifauna of the Weddell Sea through loss of critical sea ice habitat (Orgeira et al 2021). Variations in sea ice extent have implications for great whales, such as the Humpback whale Megaptera novaeangliae, since their primary prey resource is the Antarctic krill (Braithwaite et al 2015).…”