A New Bottom-Plankton Sampler

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Abstract
The sampler, which weighs about 30 kg in air, consists of a net mounted on a tubular steel sled, the latter surmounted by a diving plane. The mouth of the net is a rectangular wooden frame, in which revolves a spring-loaded door. This door is held in the open or closed position by one of two pins, which are attached on either side of the pivot of a metal ‘see-saw’ shoe beneath the frame, and which protrude through holes in the frame base into the path of the door. When in contact with the sea-bed, the rear part of the shoe is forced upwards; this withdraws one pin and releases the door, which revolves through 90° to be held by the other pin which has been forced upwards. On leaving the sea-bed, a compression spring forces the shoe downwards, so restoring the pins to their original position and the door revolves through a further 90°, to close the net mouth. Three hauls near the surface are compared with three on the bottom in 5 m depth in Red Wharf Bay (North Wales) and these show that certain of the plankters were more concentrated near the bottom.

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