Eric Tavernier

Lipid dynamics and trophic patterns in Pleuragramma antarctica life stages

Abstract The aim of this study was to clarify the trophic patterns of the key species Pleuragramma antarctica in the Dumont d’Urville Sea, through its development and possible changes according to sampling locations. Variability in diet composition of larvae, juvenile and adult P. antarctica was analysed using fatty acid markers. Analysis of lipid class in P. antarctica reflected lipid accumulation with increasing size at all sampling stations. The fatty acid composition of triacylglycerol highlighted ontogenetic changes in the diet. Phytoplankton markers, such as C16PUFA:C16 and EPA:DHA ratios >1, and carnivorous markers in larvae suggested an omnivorous diet. Comparison between the fatty acid signature of P. antarctica older stages (juveniles and adults) and zooplankton species using OPLS-discriminant analysis indicated that juveniles fed mainly on euphausiid larvae and to a minor extent on copepods, and confirmed that non-herbivorous copepods were the main prey for adults. Our results suggest that different feeding patterns and a generalist strategy in P. antarctica with juveniles feeding on bigger prey than adults, probably as a result of prey availability according to their vertical segregation pattern.

Lipid characterization of Pleuragramma antarcticum (Nothoteniidae) larvae off East Antarctica (139°E–145.10°E) during summer

Pleuragramma antarcticum (Antarctic silverfish) larvae are a key component of the neritic assemblages in the Antarctic coastal waters and can be considered as an indicator of the future changes that may occur in this area. Lipid class and fatty acid composition was studied to assess the nutritional status and evaluate the type of dominant trophic interactions of P. antarcticum larvae collected between Terre Adélie and the Mertz Glacier Tongue (139°E–145.10°E) during summer 2007. P. antarcticum larvae exhibit moderate lipid levels (11.9–15.0% dry weight). Lipid class analyses showed a similar pattern over the study area consisting mainly of polar lipids (61–75% of total lipids). During their first summer, larvae started to accumulate small amount of lipid reserves in the form of triacylglycerols (10–16% of total lipids). Polar lipids were dominated by phosphatidylcholine (55–59%) followed by phosphatidylethanolamine (19–21%). Fatty acid signature of triacylglycerols indicates (1) a dominance of copepod of the Oithona type in the trophic pattern of P. antarcticum larvae and (2) a significant contribution of phytoplankton. In the same way, the analysis of gut content shows that 70% of larvae fed on various assemblages of phytoplankton and zooplankton (mainly copepods) and 30% of larvae fed exclusively on phytoplankton. Although a carnivorous diet is commonly described, our results suggest that P. antarcticum larvae showed an opportunistic feeding strategy (i.e. high degree of omnivory) and that dietary energy seems to be mainly directed towards fast growth rather than energy storage for periods of starvation.

Trophic Ecology of Early Developmental Stages of Antarctic Silverfish

The Antarctic pelagic ecosystem over the continental shelf is dominated by the Antarctic silverfish Pleuragramma antarctica (Nototheniidae) which represents up to 90% of the fish biomass. P. antarctica is the only notothenioid species to have an entire pelagic life cycle. This species is characterized by a particularly long larval stage that lasts over a year and a vertical distribution with larvae in the surface layer and the older individuals in deeper ones. The reproductive cycle of P. antarctica is closely linked to seasonal sea ice dynamics and early stages depend on the spatial and temporal match with zooplankton production. P. antarctica is planktivorous at all stages of development, larvae are omnivorous actively feeding on diatoms and small copepods such as Oithona and Oncaea spp., while juveniles and adults are strictly carnivorous and feed mainly on copepods and euphausiids. In the early years of its life-history Antarctic silverfish exhibit primarily a marked transition in terms of trophic ecology between larvae and juveniles. The food resource partitioning is relatively clear between larvae and older life stages with a negligible overlap. Although the shift in diet between juveniles and adults remains less obvious in several geographic locations, juveniles and adults seem to share a similar mid-trophic level around Antarctica.