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International audience; One of the current challenges in today's ecology research is to understand and quantify the effects of climate changes on biodiversity. In order to detect possible trends in biodiversity patterns, it is necessary to conduct long-term observations in various and representative environments. This is always challenging, even more difficult in marine habitats and in the Southern Ocean in particular. Since 2012, a submarine observatory of the coastal benthos has been in operation in the Kerguelen Islands. Eight contrasting sites are monitored using photo and video surveys, loggers, and settlement plots. To quantify potential changes, several photographic analysis techniques are also complemented by scuba diving and ROV (Remotely Operated Vehicle) observations. Investigator scientists have developed and improved new protocols that will be carried out in the long term by the staff of the National Natural Reserve of the French Southern Territories. In order to provide reliable support of species identification, the Proteker program supported by IPEV, French Polar Institute, is currently developing several field guides that should improve the identification of the main taxa being monitored. In light of their abundance in coastal environments of the Kerguelen Islands, and because they are among the most visible invertebrates and the easiest of organisms to consider for monitoring surveys, we first focused on echinoderms. Results of this first study are presented here. For each echinoderm species, a spreadsheet provides the species name with synonymies, a description of diagnostic features, the recorded distribution, as well as three different types of illustrations: (i) living specimens in their environment, which is useful for scuba divers, (ii) fresh collected specimens out of water, and (iii) specimens fixed in ethanol. Therefore, species can be identified alive while diving, but also after sampling in the field, and after several years in the laboratory. An assessment of Kerguelen's coastal echinoderms is also given.

Ocean acidification is leading to changes in the oceanic carbonate system. As a result, calcium carbonate saturation horizon is shallowing, especially at high latitudes. Biogenic high magnesium-calcites could be particularly vulnerable, since their solubility is either similar or greater than that of aragonite. Cidaroid urchins have magnesium-calcite spines covered by a polycrystalline cortex which becomes exposed to seawater when mature (not covered by an epidermis). However, deep species live at low calcium carbonate saturation states, especially at high latitudes. We describe here the morphology and the magnesium content of Ctenocidaris speciosa spines collected at different depths from the Weddell Sea (Antarctica) and relate the features with seawater calcium carbonate saturation. We observed that the spines cortex of C. speciosa presented a thicker inner cortex layer and a lower [Mg2+] below the aragonite saturation horizon. We suggest that the cortex of cidaroid spines is able to resist to low calcium carbonate saturation state.

The present study investigates in vitro 14C D-glucose transfer across the digestive wall of the irregular echinoid, Echinocardium cordatum (Echinodermata). It aims to characterize absorption ability of the gastric caecum. The experimental device used was the Ussing chamber system. It consists of two compartments clamped together, sandwiching the digestive wall. This allows orientated measurements of radiolabelled nutrient flux through the digestive wall i.e., from the digestive lumen to the perivisceral coelomic cavity. Incorporation of 14C D-glucose by the digestive tube wall as well as the transmural flux and the total amount of 14C D-glucose transferred to the coelomic compartment were quantified. The results show 14C D-glucose incorporation in the digestive wall did not differ significantly in the stomach, the gastric caecum and the intestine whereas the amount of 14C D-glucose in the coelomic fluid was significantly higher in the intestine and in the gastric caecum than in the stomach. These observations indicate regional specialization of the digestive tube and suggest that the caecum like the intestine is an important site of nutrient absorption.