Video Plankton Recorder estimates of copepod, pteropod and larvacean distributions from a stratified region of Georges Bank with comparative measurements from a MOCNESS sampler.

Mark C. Benfield1², Cabell S. Davis¹, Peter H. Wiebe¹, Scott M. Gallager¹, R. Gregory Lough³ and Nancy J. Copley¹

¹ Department of Biology, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543
² Present Address: Coastal Fisheries Institute, Louisiana State University, 218 Center for Wetland Resources, Baton Rouge, Louisiana 70803
³ Northeast Fisheries Science Center, National Marine Fisheries Service, NOAA, Woods Hole, Massachusetts 02543

A two-vessel exercise was conducted over the southern flank of Georges Bank during the onset of vernal stratification in May 1992. The Video Plankton Recorder (VPR), a towed video system, was used to map out the fine-scale distributions of zooplankton to a depth of 70 m along a trackline which described a regular grid (3.5 x 4.5 km) in Lagrangian space. A second vessel following a parallel course conducted Multiple Opening/Closing Net and Environmental Sensing System (MOC NESS) sampling during the last section of the grid which provided an opportunity to compare data from the two systems. Both the VPR and the MOCNESS provided similar data on the taxonomic composition of the plankton which was numerically dominated by copepods (Calanus, Pseudocalanus, Oithona), pteropods (Limacina) and larvaceans (Oikopleura). The absence of rare (<43.1 m^03) species from the VPR data set was a consequence of the small volume sampled (0.0694 m^3) by the high magnification camera, while fragile gelatinous taxa were undersampled by the MOCNESS. Estimates of copepod and pteropod concentrations were comparable for the two gear types. While the species composition of the plankton did not change statistically along the grid, abundances of the dominant taxa varied along the transect and each taxon demonstrated pronounced fine-scale vertical patterns which appeared to be related to hydrographic features. The VPR represents a powerful tool for rapid surveys of the micro-to fine-scale structure of zooplankton assemblages either alone, or in conjunction with other sampling techniques.