Comparisons of Video Plankton Recorder & MOCNESS Measurements of Zooplankton from a Stratified Region of Georges Bank.

Mark C. Benfield, Cabell S. Davis, Peter H. Wiebe, Scott M. Gallager, R. Gregory Lough, and Nancy J. Copley.

Abstract for AGU 1996.

A two-vessel exercise was conducted over the southern flank of Georges Bank during the onset of vernal startification 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 MultipleOpening/Closing Net and Environmental Sensing System (MOCNESS) sampling during the last section of the grid which provided an opportunity to compare data from the two systems. Both the VPR and MOCNESS provided similar data on the taxonomic composition of the plankton which was numerically dominated by copepods (Calanus, Pseudocalanus, Oithona), pteropods (Limacina) and larvacenans (Oikopleura). The absence of rare (<43.1 m^-3) species from the VPR data set was a consequence of the small volume sampled (0.0694 m^3) by the highmagnification comera while fragile gelatinous taxa were undersampled by the MOCNESS. Estimates of copepod and pteropod concentrations were comparable for the two gear types. 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 techniqes.