Herman, A. W.. Bedford Institute of Oceanography, hermana@mar.dfo-mpo.gc.ca
, . W.. ,

We have relied on the optical plankton counter to resolve vertical distributions of zooplankton in our Scotian Shelf coastal waters primarily for assessing narrow band layers of copepods in the upper layers and copepods in the broad layers of deep basins. We first investigated the problem of calibrating our OPCs against plankton net samples for smaller copepods in the upper layers particularly in the size range of 200-500 microns where most of our problems occur. This was accomplished by conducting an intercomparison of plankton nets catches to OPC measurements to develop a methodology for intercalibrations. The experiments were conducted during our GLOBEC field program and employed a variety of sampling nets, mostly vertical haul nets, BIONESS and nets attached to the OPC itself. We revisited the classical problem of extrusion of plankton through nets while sampling simultaneously with 3 mesh sizes, 80, 140 and 202 microns and were able to quantify plankton extrusion by species and hence susceptibility to extrusion by shape and size. Among a large number of species the most dominant were copepod nauplii which fell into the 'equivalent' OPC size range of 200-300 microns and yet less than 1/30th of their numbers were retained in the 202 micron net making it less than ideal for OPC intercomparisons. The conditions for matching plankton net mesh size to OPC are described and the variability of net efficiency as a function of time/depth is related to catch efficiency for various species. Plankton counts from the nets corrected for extrusion/efficiency are compared to OPC counts and algorithms for generating plankton biomass from OPC measurements are described.
Day: Tuesday, Feb. 2
Time: Poster
Location: Sweeney Center
Code: SS23TU0460S