Swarming of Planktonic Organisms

Abstract

AGGREGATION in planktonic organisms is often observed, both in the sea and in fresh water, and several explanations have been put forward to account for it. Uneven light intensity can often lead to aggregation; but other reasons must be put forward to account for swarms under uniform illumination. Some authors consider the animal's own behaviour to be responsible for swarming; thus social behaviour has been invoked in Cladocera¹, chemosensitivity in Hemimysis² and visual orientation to explain Mysid shoaling³. Other authors regard physical processes as being largely or entirely responsible, such as wind-generated turbulence⁴, retention in convection cells⁵ or in a weak convergence, aided by photopositive swimming⁶.