Zooplankton counters

Figure 1. The Batfish vehicle with its full complement of sensors a Va-riosens fluorometer, a digital CTD unit, and the prototype electronic zooplankton counter with its sampler net (7).

Electronic Zooplankton Counter. The electronic zooplankton counter (prototype) mounted on Batfish operates on a principle similar to the Coulter counter where an insulating particle, such as a zooplankter, displaces seawater in a tubular cell and causes a change of electrical con-... 

The in situ Batfish sampler does not provide seawater samples for on-deck analysis. Therefore, we have also developed a continuous profiling pumping system (11) that measures biological profiles of copepods and chlorophyll and temperature while on station. Copepods and chlorophyll are measured on deck from the hose effluent with a deck-mounted electronic zooplankton counter and Turner 111 fluorometer. Measured profiles of copepods and chlorophyll indicate a vertical resolution of 3-4 m while the pumping system delivers — 50-60 L/min of seawater on deck. 

For quantifying zooplankton abundance and depth distribution, particle counters have been developed on the basis of commercially available five-electrode conductivity cells, which are similar in concept to those used on Batfish (20-22). Particle counters have particular application for counting fish eggs or larvae that fall in narrow bands (mackerel eggs are 1.3 0.1 mm in diameter), or the dominant species of copepod in any plankton assemblage. 

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