Zooplankton abundance and community structure over a 4000 km transect in the north-east Atlantic

Zooplankton samples were collected by a high speed sampler, the U-Tow, in t he north-east Atlantic between 61.6 and 36.7 degreesN during June and July 1996, and were used to examine the causality of spatial distributions along a 4000 km transect. Peak zooplankton abundance and biovolume estimations w ere associated with a frontal system at 48-52 degreesN, which separated hyd rographically distinct water masses. The zooplankton assemblage was dominat ed by herbivorous/omnivorous taxa in the northern regions, and by carnivoro us taxa in the souther regions. Arguments are developed to suggest that the switch in both the zooplankton size structure and trophic status, centered within the frontal region, are consistent with 'bottom-up' control of zoop lankton size structure in this region of the Atlantic.