Vertical distribution (0-1000 m) of macrozooplankton, estimated using the Underwater Video Profiler, in different hydrographic regimes along the northern portion of the Mid-Atlantic Ridge

The vertical distribution (0-1000 m depth) of macrozooplankton along the northern portion of the Mid-Atlantic Ridge (59 degrees 58N, 25 degrees 53W to 41 degrees 29N, 28 degrees 19W) was investigated during the MAR-ECO program (June and July 2004) using the Underwater Video Profiler (UVP). Twelve relatively large (> 1 cm) groups were selected from the recorded images: sarcodines (with two sub-groups), crustaceans (excluding copepods), chaetognaths, ctenophores (with two sub-groups cyclippids and lobates), siphonophores, medusae (with three subgroups Aeginura grimaldii, Aglantha spp. and all other medusae), appendicularians, and thaliaceans. The numerically dominant groups over the whole area were crustaceans (26%), medusae (20%) and appendicularians (17%). The gelatinous fauna were consistently most numerous at 400-900 m. Appendicularians, ctenophores and Aeginura grimaldii occurred mostly below 300 m (maximum concentrations of 75, 58, and 30 individuals 100 m(-3), respectively). Sipbonophores, Aglantha spp. and the other medusae were more uniformly distributed in the water column (maxima of 42, 42 and 300 individuals 100 m(-3), respectively). The macrozooplankton community below 200 m varied with the spatial distribution of the water masses, suggesting that the Sub-Polar Front restricts the mixing of macrozooplankton communities down to 1000 m depth. (c) 2007 Published by Elsevier Ltd.