ARCTOS network

Abstract of PhD thesis

Nutrition and lipid dynamic of the hyperiid Themisto libellula. Importance in terms of adaptive strategy.
Relatively few studies exist on the amphipod Themisto libellula despite a large distribution in the Arctic and high abundances.
Due to its carnivorous diet and as a prey for higher predators, this species might represent an important trophic link in the pelagic food chain and contribute significantly to the energetic transfers.
The two objectives of this thesis were: i) to understand how T. libellula adapts to polar conditions, ii) to know its trophodynamic role. In 2006 and 2007, from May to October, sampling and experiments were conducted in Kongsfjorden, a fjord located on the western coast of Svalbard (79° N).
Results revealed that dietary energy inputs were invested in growth during the first months of their life (spring) then stored as lipids of high energy value (summer-fall). Fatty acids trophic markers indicated a diet shift during their development; a mix diet composed by phytoplankton-zooplankton was identified in younger individuals and older individuals preyed mainly upon Calanus copepods.
Gut content analyses have been done and confirmed the presence of a significant amount of chlorophyll a in juveniles. Complementary predation experiments allowed determining daily ingestion rates and selectivity of T. libellula. Globally, results showed a good synchronization between life cycle of T. libellula and seasonal dynamic of lower trophic levels.
Overabundance of food resources compared to their needs and low predatory pressure on T. libellula in the studied area suggested that Kongsfjorden constitutes an ideal nursery for juveniles and sub-adults of this species.