HIGH-RESOLUTION OBSERVATIONS OF PLANKTON SPATIAL DISTRIBUTIONS CORRELATED WITH HYDROGRAPHY IN THE GREAT SOUTH CHANNEL, GEORGES BANK

During a cruise to Georges Bank in May 1992, the Video Plankton Record er (VPR) was towyoed while non-invasively obtaining images of the plan kton and environmental (CTD)data. Data from an 8 h transect across the Great South Channel (GSC) were analyzed on a continuum of spatial sca les from coarse-scale (100 km) to micro-scale (mm). Abundance was dete rmined for 12 taxonomic groups including: invertebrate larvae (ophiopl uteus larvae, anthozoa larvae: Cerianthus sp.), hydroids, copepods (Ca lanus sp., Pseudocalanus sp.), pteropods (Limacina retroversa, Clione sp.), ctenophores (Mnemiopsis sp., Pleurobrachia sp.), larvacea (Oikop leura sp.), chaetognatha (Sagitta sp.), and diatom colonies (Chaetocer os socialis). Species-specific plots of the positions of individual pl ankton in the water column and plots of the temperature and salinity a t which the plankton were observed (temperature-salinity-plankton plot s) showed that major taxonomic groups were patchy at coarse scales bec ause of their association with specific water masses of different orig in and associated temperature/density discontinuities (pycnocline and fronts). Analysis of,the T-S characteristics of water types indicated that diatom colonies and ophiopluteus larvae of echinoderms were trans ported to GSC in a band of coldwater originating on the south flank of Georges Bank. Within this band, diatom colonies formed an intense pat ch at a front reaching a density of 5 ml(-1). Within each water mass, fine-scale (10s of meters) plankton patchiness was associated with reg ions of vertical stability as indicated by the association of plankton with regions of high gradient Richardson number. Aggregation of plank ton at the microscale (<1 m) occurred significantly only for plankton capable of active swimming, suggesting a dynamic interaction between b iological and physical variables at this spatial scale. On occasion, v eliger larvae of Limacina retroversa were found in spawning patches at concentrations exceeding 600 ml(-1) within a few centimeters of the a ir-sea interface. The ability to observe and quantify local concentrat ions of plankton together with micro-scale physics, but over broad spa tial scales, will help provide information on the coupling between spa tial scales necessary to understand how individuals interact to form p opulations and communities in the world oceans. Copyright (C) 1996 Els evier Science Ltd.