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The marine ecosystem provides numerous goods and services, dampens the impacts of floods and storms, and provides climate control, through the regulation of carbon fluxes, nutrient cycling, and the bioremediation of human waste and tourism. However, the ocean is vulnerable to anthropogenic threats and has been severely altered by humans.Seabirds and marine mammals are long lived, highly mobile, easily identifiable, and occupy the upper levels of trophic webs. These ecological features make them suitable as sentinels of the marine ecosystem.Sighting data collected during eight oceanographic surveys were analysed to describe and compare the biodiversity of the communities of top predators within the marine protected areas (MPAs) of Namuncurá/Burdwood Bank I and II and the surrounding areas in two contrasting seasons (summer and winter). Data were grouped into six zones based on depth and geographic position.Twenty‐five species of seabirds and 13 species of marine mammals were recorded in 113 days of surveys between 2014 and 2018. Top predator community composition varied seasonally in the different zones.A suite of indicator species was identified according to their specificity and fidelity to a particular zone. Most of the species identified as potentially useful indicators differed between summer and winter, highlighting the importance of conducting systematic surveys in both periods.The MPAs Namuncurá/Burdwood Bank I and II are key areas for top predator communities in the region, mainly in summer when the number and abundance of species increase. However, the waters around Isla de los Estados and the channel between Isla de los Estados and Burdwood Bank were also identified as a relevant habitat for many species. This knowledge should be included to create a regional network of areas under special management considerations that connect the established MPAs with other key pelagic and coastal areas (as found in this study) for the conservation of subantarctic marine megafauna. [ABSTRACT FROM AUTHOR]

Cetaceans are known to play an important role in ecosystem structure and dynamics because they occupy the highest position in food webs. In order to improve our knowledge on the feeding ecology of the long finned pilot whale, Globicephala melas edwardii, in the western South Atlantic Ocean, we analyzed carbon (δ13C) and nitrogen (δ15N) stable isotope composition of bone collagen from 54 specimens found stranded along the coast of Tierra del Fuego, Argentina. Through Bayesian mixing models we estimated the contribution of the most putative prey to the consumer's diet. Prey species were selected, based on previous knowledge and covered all possible foraging areas for the region that were analyzed through a visual spatial analysis (based on sightings records). Based on our results, the long finned pilot whale is mainly a teutophagous species, feeding on squids, and can complement its diet with neritic prey when moving sporadically to coastal areas. We found that the southeastern part of Tierra del Fuego, north of Staten Island and the slope break around the Burdwood Bank are plausible feeding areas, which offer suitable habitats where pilot whales can search for their preferred prey. These areas are important for Argentin's conservation policies, since they enclose three oceanic Marine Protected Areas (Namuncurá–Burdwood Bank, Burdwood Bank II and Yaganes). Therefore, it is crucial to improve the knowledge regarding their foraging preferences in order to provide support for conservation and management strategies in these MPAs. [ABSTRACT FROM AUTHOR]