Despite the important ecological role of cephalopods in energy and material flow in marine ecosystems, they are poorly understood, particularly those inhabiting deep-sea bottoms below 800m. To define cephalopod species assemblages from the upper to the lower slope, we conducted 13 oceanographic and trawl surveys in the Balearic basin (NW Mediterranean) in 198592 and 200710 at depths between 450 and 2200m. Multivariate analysis suggests the existence of three assemblages on the upper (450600m), middle (6501500m) and lower (16002200m) slopes. Although seasonal changes in species abundance and composition were evident, no significant variations in the assemblage structure were observed between the two time periods. Two main trophic pathways involving deep-sea cephalopods were apparent: species mainly linked to benthic resources and species mostly connected to the pelagic food web through active swimming and frequent vertical migrations. Accordingly, two environmental variables best explained the observed patterns: net primary production and river discharge. Phytoplankton availability controls the increase of zooplankton that influences the distribution and abundance of pelagic cephalopods. River discharge affects, in some instances with delays, transfer of organic matter to the benthic trophic pathway and thus to bottom-dwelling cephalopods. © 2012 CSIRO.

cited By 12