Abundance, distribution and size structure of zooplankton along a 20 degrees west meridional transect of the northeast Atlantic Ocean in July

Zooplankton distribution, abundance and size structure were characterised o n leg 2 of the PRIME cruise in the northeast Atlantic during July 1996. Lat itudinal sampling was carried out from 60 degreesN to 37 degreesN along a m eridian at approximately 20 degreesW. Zooplankton were characterised using an Optical Plankton Counter (OPC), and from traditional depth-integrated ne t hauls for taxonomy and carbon. The former method allows zooplankton to be described in terms of biovolume and size. There was good agreement between the two methods for abundance and a good correlation between OPC biovolume and carbon analysis. These data also showed compatibility with concurrent acoustic measurements of zooplankton. Results for the cruise compared to re cent studies in the region, show that, overall abundance was generally low, although most of the previous studies were closer to spring bloom conditio ns. The size structure over latitude shows that mean size fluctuated, but t here was a general trend of decreasing mean size from the north of the tran sect to about 47 degreesN. Further statistical treatment of the OPC data, u sing principal component analysis, showed that zooplankton size structure c hanged at five positions along the transect. Three of these coincided with changes in physical structure, one each side of the front at 48 degreesN an d the third on the outer edge of an eddy. The other two occurred in regions of high-surface chlorophyll concentration. (C) 2001 Published by Elsevier Science Ltd.