Amphipods in sediment traps of the eastern Fram Strait

Life-cycle characteristics of the free-swimming lysianassoid amphipod Cyclocaris guilelmi were investigated and compared to those of other regularly appearing amphipods in the Arctic deep-sea community. In this context we analysed time-series data of meso- and bathypelagic amphipods collected as swimmers in moored sediment traps from 2004 to 2008 at the deep-sea long-term observatory HAUSGARTEN (79°N/4°E) in the eastern Fram Strait, Arctic Ocean. Six mesopelagic and three bathypelagic deep-sea amphipod species regularly occurred in the traps. The lysianassoid C. guilelmi showed a stable interannual population size and seasonal peaks in its occurrence from August to February during the five-year sampling period. The investigation of its population structure and reproduction ecology indicated year-round breeding behavior of this species. Up to 4 cohorts consisting mainly of juvenile and female C. guilelmi were observed. We conclude that C. guilelmi plays an important role within the Arctic amphipod deep water community.

Nematodes and meiofauna in sediments obtained from RRS Discovery cruise D297, Portuguese continental margin

Samples collected in the deep Nazaré Canyon and at the adjacent slope, during the HERMES RRS Discovery D297 cruise (2005), were analysed for metazoan meiofauna, nematode structure and diversity and its relation to quality and quantity of sedimentary organic material. The amount and quality of organic matter available for direct consumption was much higher in the canyon compared to the slope and positively correlated with high nematode abundances (795-1171 ind. 10 cm**-2) and biomass (93.2-343.5 µg dry weight 10 cm**-2), thus leading to higher standing stocks. Canyon nematode assemblages also showed particular adaptations (e.g. higher trophic complexity, variability of nematode morphology, and presence of opportunistic genera) to canyon conditions, particularly in the deeper sediment layers. The Nazaré Canyon's nematode diversity was slightly lower than that of the adjacent slope and its assemblages were characterised by a higher dominance of certain genera. Still, the canyon contributes considerably to total Western Iberian Margin diversity due to different assemblages present compared to the slope. Furthermore, the harsh conditions in terms of hydrodynamic disturbance and the high organic matter flux are likely to have a negative impact on the establishment of species rich meiobenthic communities, especially in the canyon axis.