Measuring abundance and size distribution of zooplankton using the optical plankton counter in underway mode

The Optical Plankton Counter (OPC) is an optical instrument capable of large scale, rapid and continuous counting and sizing of zooplankton. A towed and a laboratory version of the instrument is available. A novel application of the laboratory model, in underway mode using a ship's uncontaminated sea-water supply, is the subject of this paper. The work was carried out aboard the RRS James Clark Ross, the British Antarctic Survey (BAS) research and supply vessel, on her annual voyage south from the UK to the Falkland Islands during September and October 1995. The instrument and its application are described, together with a review of some of the operational issues arising from such an application of the instrument. Samples of the data are presented, to illustrate the scale of sampling possible with the system compared with traditional methods. Some validation data from laboratory microscopic taxonomic analysis are also presented.