Abstract:
This Thesis describes the variation of the meroplankton communities in oceanic and coastal waters of the Ross Sea, Antarctica and hypothesizes the changes on a species distribution with future climate conditions, combining information from adult and larval environmental suitability. This work relies on the accurate identification of larval specimens. Using a morphological and molecular approach, DNA sequences obtained from specimens morphologically identified as Operational Taxonomical Units (OTUs) were aligned with reference sequences and a final identification was achieved using phylogenetic trees. In the oceanic Ross Sea, 68 of the original OTUs have been reclassified: we have been able to detect and discard from further analysis 15 holoplanktonic molecular OTUs (mOTUs) and identified 43 mOTUs from eight phyla. In the oceanic Ross Sea - investigated as part of the IPY-CAML voyage to the Ross Sea – the overall larval abundance was lower than in previous Antarctic studies (5.19 specimens per 100 m3) and was significantly higher in the first 200 m of the water column without showing any variation across regions. Alpha diversity showed regional variation and it was significantly higher over the Ross Sea Shelf than over the slope or the offshore Antarctic; and without any depth variation. The community composition varied significantly across depth and regions, and we found a weak but significant Spearman correlation between changes in community composition and a combination of three environmental variables (temperature, depth and latitude). The coastal sampling scheme - part of the Latitudinal Gradient Project - studied three sites in a latitudinal gradient along the Victoria Land coast: Cape Hallett, Terra Nova Bay and Granite Harbour. We did not find any significant latitudinal pattern on larval abundance, alpha diversity or number of OTUs, and it was in the community composition where a strong, significant regional pattern arose. These differences were driven by a combination of locally abundant and widespread species. We found no evidence of a latitudinal variation in the feeding strategy of larvae. Terra Nova Bay, the mid latitude site, showed the highest proportion of planktotrophic larvae (0.95), while Cape Hallett and Granite Harbour showed similar proportions (0.73 II planktotrophy in Cape Hallett and 0.7 in Granite Harbour), thus giving evidence of the prevalence of planktotrophy at high latitudes. The importance of dispersal stages on determining changes in a species distribution was shown. Using georeferenced larval and adult records, two species distribution models were constructed with MaxEnt, which were projected into future (2050) climate conditions. This projection has revealed a decrease on suitability for both life stages, but the dramatic drop in larval suitability in the Ross Sea predicts a population collapse in that area.