Dynamics of benthic copepods and other meiofauna in the benthic boundary layer of the deep NW Mediterranean Sea

A continuous high-resolution time-series survey of the hyperbenthic community and local environmental conditions was conducted in the benthic boundary layer (BBL) of the DYFAMED-BENTHOS station (43 degrees 24.61'N, 7 degrees 51.67'E at 2347 in depth in the NW Mediterranean) between January 1996 and April 1998 using bottom-moored sediment traps and a current meter. Sediment traps were set 4 m above the bottom. Hyperbenthos was collected as 'swimmers', i.e. those organisms that are alive when they enter the traps but are not part of the particle flux. Identification of these organisms showed that similar to 90%, were meiobenthic, Copepods dominated and comprised on average 75%, of total swimmers. They were followed by nauplii (12%), annelids (7.8%), nematodes and bivalves (1.8%, each), ostracods, isopods, and amphipods (1.2%, altogether). Of the 3930 copepods examined, 4%, were calanoids, 15% were harpdcticoids and 81% were cyclopoids. Among the non-calanoid copepods, 25 species or groups of species were distinguished. Two benthic copepod species outnumbered all others: the cyclopinid genius Barathricola represented 90%, of the cyclopoids, and the tisbid genus Tisbe represented 57%, of the harpacticoids. Temporal variations, both intra- and interannual, in swimmer fluxes were high (26 to 361 ind. m(-2) d(-1)), but not all groups/taxa/species were equally affected. Statistical analyses showed that these variations were the result of variability in both physical (near-bottom current) and trophic (particle flux) environmental factors. Organisms had both immediate and delayed responses, which involved passive (i.e. erosion, suspension) and active (i.e. emergence) reactions, as well as population growth. Most of the dispersal mechanisms previously reported for shallow-water benthic organisms were encountered, denoting the remarkable similarities in the general processes between coastal and deep-sea environments.