Body mass and lipid dynamics of Arctic and Antarctic deep-sea copepods (Calanoida, Paraeuchaeta): ontogenetic and seasonal trends

Ontogenetic and seasonal trends in body dry mass (DM) and total lipid content were studied in polar species of the predatory calanoid copepod genus Paraeuchaeta. Analyses included the Arctic representatives Paraeuchaeta glacialis, P. norvegica, P. barbata, and P. polaris as well as the Antarctic congener P. antarctica and one sample of P. cf. biloba. A total of 567 samples including 7007 individuals collected during four Antarctic and six Arctic research cruises was processed to provide seasonal coverage from spring to fall for both areas investigated, the Antarctic Weddell Sea and Arctic Fram Strait. All epipelagic species, i.e. P. glacialis, P. norvegica, and P. antarctica, showed a continuous increase in body DM from early copepodite stage CI onwards to stage CV. On average, body mass tripled with every moult. In females, body mass tripled again during the last moult to adulthood, whereas adult males, which have reduced mouthparts and do not feed at all, did not significantly increase their body mass after moulting from the CV stage. In contrast, early stages, i.e. nauplii to copepodids CII, of the bathypelagic species P. barbata remained at similar DMs. The deepest living species P. polaris was characterised by relatively large juvenile stages but small adult females, resulting in a rather small increase in body mass during ontogenetic development. Total lipid content decreased from maximum values of 60-70% of DM in eggs and early copepodite stages to <20-30% DM in stage CIII. Starting with stage CIV, lipids were again accumulated leading to high values of 40% to >50% DM in adult females. Distinct differences were detected with regard to seasonal trends of body mass and lipid content between epipelagic and bathypelagic species: Copepodids CIV, CV and adult females of epipelagic species exhibited highest body masses and lipid contents in fall, whereas for the deeper-living P. barbata maximum values occurred in spring. These discrepancies are discussed in relation to reproductive patterns and differences in abiotic and biotic environmental factors between the epipelagic and bathypelagic zones.