[en] Sea stars (Echinodermata: Asteroidea) are a key component of the Southern Ocean benthos, with 12% of the known sea star species living in the Southern Ocean. This group is considered quite resistant to seawater temperature changes. However, it is still likely to be impacted by the modifications of environmental conditions and food web functioning linked to climate change occurring in the Southern Ocean. Indeed, reduced abundances or disappearance of common prey put sea star populations at risk. However, trophic diversity, and notably capacity to switch prey according to environmental conditions (i.e. trophic plasticity) could help Southern Ocean sea stars to cope with climate-induced modifications of food web functioning.
Western Antarctic Peninsula is one of the most rapidly warming regions of the world, resulting in sharp decreases in sea ice cover and ice season duration. In this context, this study used stable isotopes ratios of C (hereafter referred to as δ13C) and N (hereafter δ15N) to investigate the trophic ecology of sea stars and characterise their trophic diversity and plasticity along the continental shelf of Western Antarctic Peninsula. Sea stars were sampled during the austral summer in the South Shetland Islands, the South Orkney Islands and in Marguerite Bay. Intra- and interspecific patterns in trophic diversity were investigated in each region using isotopic dispersion as well as isotopic niche (proxy of the realised ecological niche) areas and overlap.
In South Shetland and South Orkney Islands, sea stars were sampled far from the sea ice edge. In Shetland Islands, there was no difference of δ13C values between species or between the islands, indicating that sea stars of this region could rely on a common basal food source such as sinking phytoplankton. The overlap between the isotopic niches of sea star species was also important and sometimes complete at the scale of the whole region. Sea star species from South Orkney Islands had more variable δ13C but usually similar δ15N, suggesting a better source partitioning than in Shetland Islands, but also that species are feeding at more similar trophic levels than in these islands. Finally, sea stars from Marguerite Bay were sampled near the melting sea ice edge. Sea stars from this region could rely on both organic matter released during sea ice melting and sinking phytoplankton. This is highlighted by 1) high variation of δ13C values between species and sampling areas and 2) low overlap between isotopic niches. Overall, difference in niche partitioning and overlap between the regions may be linked with different environmental conditions, including sea ice coverage and dynamics.
This research was funded by the Belgian Federal Science Policy Office (BELSPO) in the framework of the vERSO and RECTO projects (rectoversoprojects.be).
