IMIS

A double sampling strategy was set up to maximise the scope of this PhD thesis. First, sea stars were collected in the Southern Ocean during campaigns taking place in the framework of the vERSO and RECTO projects from December 2015 to March 2017. Second, suitable samples originating from multiple oceanographic campaigns and surveys from January 1985 to January 2015 were retrieved from archived collections stored in museums or institutions. Institutions that provided samples included the Université Libre de Bruxelles (Belgium), the National Museum of Natural History (Paris, France) and the Institute of Oceanology of the Polish Academy of Sciences (Sopot, Poland).
Sampling: Sea stars were sampled in the Southern Ocean from 1985 to 2017 throughout multiple oceanographic campaigns. Storage: Depending of the sampling campaign, sea stars were frozen, dried, stored in ethanol or fixed with formaldehyde and then stored in ethanol. Sample preparation: For each sea star, one or several arms were separated from the central disc. Internal organs and podia were removed in each arm. With the exception of the already dried samples, the tegument and the podia of each arm were washed with demineralised water and oven-dried at 50°C during 48 hours. All samples were then homogenised into powder. Carbonates were removed from subsamples by exposing subsamples to 37 % hydrochloric acid vapour during 48 hours. Acidified subsamples were then kept at 60°C until further sample preparation. Stable isotope analysis: The subsamples were then precisely weighed (ca 2.5-3 mg) in 5×8 tin cups with ca 3 mg of tungsten trioxide. Their elemental composition and their stable isotope values were analysed with an elemental analyser coupled to a continuous-flow isotope-ratio mass spectrometer. Impact of preservation on stable isotope values: Correction factors were added to the δ13C and δ34S values of sea stars fixed with formaldehyde and/or stored in ethanol as fixation in formaldehyde and preservation in ethanol impact stable isotope values in sea stars (Le Bourg et al., 2020). For samples stored in ethanol, a correction factor of –0.6 ‰ was subtracted to δ13C values. For samples fixed with formaldehyde and then stored in ethanol, a correction factor of 0.2 ‰ was added to δ13C values to take into account the effects of both ethanol (–0.6 ‰) and formaldehyde (+0.8 ‰) on δ13C values. A correction factor of 1.5 ‰ was also added to δ34S values for samples fixed with formaldehyde. Reference: Le Bourg B, Lepoint G, Michel LN. 2020. Effects of preservation methodology on stable isotope compositions of sea stars. Rapid Communications in Mass Spectrometry 34, e8589.