Using fish to identify ecological regions
Fish are helping scientists identify different ecological regions in the Dumont d'Urville Sea.
The Dumont d'Urville Sea, ranging from Terre Adélie to the Mertz Glacier tongue, in George V Land was investigated during the Collaborative East Antarctic Marine Census (CEAMARC) to understand the composition of the marine biota in relation to their environments, and to establish baseline information that could be used to track changes over time.
Historical surveys listed about 20 species of fish, but we have now identified 91 species belonging to 21 families. This shows the importance of having integrated international surveys. Fifty-one per cent of the species belonged to the Notothenioids, a group highly endemic (or specific) to the Southern Ocean shelves (such as icefish, toothfish and Antarctic silverfish). These are followed by Myctophids (lantern fish), a deep sea family very abundant in the Southern Ocean that migrates from the deep layers (greater than 200 m) to the surface layers.
Different ecoregions were found in the pelagic and continental shelf zones. In the pelagic zone, we found a clear distinction in species composition between the surface water layer (0–200 m), the intermediate layer (200–600 m) and the deep layer.
The continental shelf regionalisation, based on fish living near the sea floor, showed a clear difference between continental margins, inner-shelf depressions, banks and coastal zones. Some species were caught specifically in inner-shelf depressions and especially in the George V Basin. This shelf regionalisation is probably related to both recent environmental features and past environment. Further investigation is needed to determine if colonisation of the shelf occurred from the continental margin itself, or from shelter sites over the shelf that were not covered by ice, after Last Glacial Maximum.
What have we learned from CEAMARC? The list of species known for this area has increased for all the taxa, especially for fish but also for gelatinous plankton and benthos. The Mertz Glacier tongue broke off at the beginning of the year, releasing a very large iceberg. This will change the currents and the biological productivity of the area, it will impact benthic communities (organism living on the sea floor) by scouring, and it will then modify fish habitats. Other surveys in the Dumont d'Urville Sea will try to follow the consequences of this major change in the area. Some will be led by the Australian Antarctic Division, others like the French ICO²TA project (Integrated Coastal Ocean Observations in Terre Adélie) supported by Institut Polaire Paul Emile Victor, will continue to study the changes in the pelagic environment (plankton and pelagic fish) each year.
Observatoire Océanologique de Villefranche sur Mer, France