Biology of meso- and bathypelagic chaetognaths in the Southern Ocean

Chaetognaths contribute significantly to the zooplankton abundance and biomass in the world ocean. Stratified sampling between 500 and 2000 m depth with small mesh sizes in the Atlantic Southern Ocean has provided a unique opportunity for a detailed investigation of meso- and bathypelagic chaetognaths. The chaetognath community consisted of ten species with Eukrohnia hamata and Sagitta marri dominating. E. bathypelagica and E. bathyantarctica were characteristic deep-living species. Water depth and season were the determinants of chaetognath abundance and species composition patterns, indicating vertical seasonal migration and vertical segregation of species. Reproduction may be continuous in E. bathypelagica and E. bathyantarctica. These two deep-living species do not store high amounts of lipids and therefore rely on food supply year-round. However, their diet seems to be different because of their varying fatty acid compositions. The impact of meso- and bathypelagic chaetognaths on the copepod community in the Southern Ocean is probably significant and they may hold a central position channelling energy from lower to higher trophic levels.