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A diver-controlled plankton net

Many types of plankton net have evolved for various sampling needs, but in the main they are designed for sampling in mid-water, or over fine particulate substrates where they can operate within a sledge frame. The conventional plankton nets are mostly towed behind a boat and can only be used in areas where there are no obstacles to impede their course. Many nets are described in the literature and the reviews by Tranter et al. (1966) and the UNESCO monograph on zoological sampling methods (Tranter, 1968) give further details. Nets for taking benthic plankton are generally mounted on a sledge frame and either towed behind a boat (Russell, 1928; Wickstead, 1953), towed in shallow water by persons wading and pulling the net behind them (Colman & Segrove, 1955) or pushed by SCUBA divers (Fager et al. 1966). However, all these methods still leave the need to sample rocky areas and irregular substrates where conventional methods are not possible. Such areas are often extremely rich in planktonic organisms which appear to accumulate within the shelter offered by gulleys and depressions in the bottom topography (personal observation). Often species associated with inshore algal belts are poorly represented in conventional offshore plankton samples (Russell, 1973), and it may be that such species spend much of their larval existence close in shore or in association with shallow water reefs. The present paper describes a diver-controlled plankton net which has been designed to sample rocky areas. By having direct diver control this plankton net can be used to sample other areas where conventional methods are not appropriate.