Comparative population structure, abundance and vertical distribution of six copepod species in the North Atlantic: Evidence for intraguild predation?

The abundance, vertical distribution and stage composition of the copepods Euchaeta norvegica, Metridia lucens and Pleuromamma robusta and the abundance and vertical distribution of Acartia sp., Oithona spp. and Oncaea sp. were analysed for a period of 4.5 years (1971-1974), based on data previously collected at weather station India in the North Atlantic (59°N, 19°W). The results were compared with previously published results on Calanus finmarchicus during the same study. The factor analysis showed two well-differentiated groups. The cohort development and abundance of C. finmarchicus, E. norvegica and Oncaea were related to successive phytoplankton blooms. On the contrary, the cohort development and abundance of M. lucens, P. robusta, Acartia spp. and Oithona spp. were not related to phytoplankton concentration and showed negative relationships with Calanus abundance. We suggest that C. finmarchicus, which largely dominates the biomass at station India, could play a key role in the structuring of the community: as prey for the carnivorous E. norvegica, vectoring the spring bloom to deep waters through faecal pellet consumption by the coprophagous Oncaea spp., and through intraguild predation on the early stages of other omnivorous copepods such as Acartia, Oithona, M. lucens and P. robusta.