TRANSOCEANIC CHARACTERIZATION OF ZOOPLANKTON COMMUNITY SIZE STRUCTUREUSING AN OPTICAL PLANKTON COUNTER

The Atlantic Meridional Transect (AMT), sampling between 50 degrees N and 50 degrees S, is a trans-oceanic research programme to characteriz e plankton community structure, productivity and bio-optical propertie s of the upper ocean in relation to ocean provinces and meso-scale fea tures. As part of a suite of continuous measurements, an optical plank ton counter (OPC) has been used on the AMT to characterize the surface distribution of zooplankton based on their abundance and community si ze structure. Results from the OPC were available in real time, and we re subsequently validated against microscope counts of zooplankton sam pled concurrently along the AMT. Zooplankton community size structure from two sections of the Transect are presented: from the northern edg e of upwelling off West Africa to the UK shelf and between the Falklan d Islands and Uruguay, where the Transect traversed a warm core ring. Results showing the zooplankton community size structure together with statistical analysis, using principal component analysis (PCA), are c ompared with the dynamic oceanographic characteristics along the Trans ect. The application of the OPC for such basin-scale studies provides a methodology for obtaining data on zooplankton abundance and communit y structure at the appropriate spatial scales for global-scale modelli ng of the marine ecosystem.