ESTIMATES OF ZOOPLANKTON ABUNDANCE AND SIZE DISTRIBUTION WITH THE OPTICAL PLANKTON COUNTER (OPC)

The capability of the Optical Plankton Count er (OPC) to examine the a bundance and size distribution of zooplankton was tested in Storfjorde n, Norway, in June 1993. Selected material obtained from net sampling was measured with a laboratory version of the OPC and compared with mi croscope analysis in order to identify main species in the in situ siz e frequency distributions obtained by the submersible version of the O PC. Differences in the particle concentration between shallow and deep water layers were clearly resolved by the submersible OPC, but the hi gh diversity of the zooplankton community and widely overlapping size ranges prevented a detailed analysis of the fine scale vertical distri bution and the horizontal variability of abundance for distinct specie s. These results are used to discuss the limitations of the OPC for ra pid and continuous surveying of spatial distribution and abundance of zooplankton.