The vertical distribution, trophodynamics and reproductive strategies of Arctic deep-sea copepods of the families Aetideidae and Euchaetidae were studied at 19 stations in the Greenland Sea, Fram Strait and the adjacent Arctic Ocean. Results from field work, analytical and experimental approaches are combined to assess the impact of the meso- and bathypelagic copepods on the carbon flux within Arctic deep-sea ecosystems. Furthermore, general concepts concerning pelagic biodiversity and interspecific competition are highlighted and discussed.

A total of 4 euchaetid and 7 aetideid species were identified. Within both families, congeners were generally restricted to distinct depth strata, thus vertically partitioning the water column. For example, in the central Greenland Sea Chiridius obtusifrons occupied the mesopelagial from 100 to 500 m depth, whereas Aetideopsis minor was concentrated in 500 to 1000 m and A. rostrata inhabited the bathypelagial below 1000 m. In the northern part of the investigation area the vertical ranges of most species were shifted upwards, thus supporting the widely established concept of a polar emergence. The multi-layered distribution pattern, however, remained principally the same. Boreal-Atlantic species were absent from the polar NE Greenland shelf and Nansen Basin. Nevertheless, they occurred abundantly at 82°N over the Yermak Plateau, where their distribution reflected the inflow of Atlantic water masses into the Arctic Ocean. This observation supports the hypothesis that a branch of the West Spitsbergen Current extends northward along the western flank of Yermak Plateau.

With respect to reproductive strategies, strong differences were detected among Pareuchaeta species. Epi- to mesopelagic congeners produced high numbers (40 to >50) of relatively small eggs, while bathypelagic forms relied on larger, energy-rich eggs at the expense of reduced egg numbers (4 to 19). The increase of egg size and energy content with depth is interpreted as an adaptation to the food-limited conditions of the deep-sea. A lecithotrophic development based on the enhanced energy reserves within the eggs makes young stages of bathypelagic species less dependent on external food sources. In contrast, high offspring numbers may be important for epipelagic species to counter higher predation risks.

Differences in feeding behavior and dietary composition among Euchaetidae and Aetideidae were studied by lipid biomarkers and feeding experiments. Based on the vertical distribution, dietary composition and reproduction strategies, the question is discussed as to which mechanisms act to minimize interspecific competition among closely related sympatric species in the food-limited deep-sea environment. In general, congeneric species are restricted to distinct vertical ranges and partition the water column. Different feeding preferences reduce competition mainly between sympatric genera. However, in the case of the dominant Pareuchaeta glacialis and P. norvegica re-colonization processes triggered by the complex current system and hydrographic-biological interactions are the keys to understanding their sympatric distribution.

Individual ingestion rates were determined by feeding experiments, respiration measurements and by an allometric approach based on body mass. Predatory Pareuchaeta ingested 4 to 6.7% of body mass per day. The potential ingestion of Pareuchaeta populations was substantially higher than the secondary production of their principal prey Calanus, meaning that predation by Pareuchaeta may control prey population growth (top-down control). Moreover, omnivorous aetideids may consume more than 40% of the vertical carbon flux. Hence, they significantly contribute to pelagic-benthic coupling processes. In conclusion, the study demonstrates that Aetideidae and Euchaetidae are prominent members of the Arctic deep-sea ecosystem and play important roles with regard to the energy and carbon flux.