Diel variation in the vertical distribution of some common zooplankton species off the west coast of South Africa

Abstract

The vertical distribution and the diel variation of seven species of copepods and the euphausiid Euphausia lucens were examined over a 28-hour period covering 20—21 May 1978 in an area approximately 65 km north-west of Cape Columbine. The majority of the copepod species remained within the sampling depth (0—85 m) and showed no marked diel movement. Those that did migrate (Nannocalanus minor and Metridia lucens) showed evidence of reverse migratory behaviour. There was ontogenetic layering in the vertical range of Euphausia lucens. While the calyptopis larvae remained near the surface and did not migrate, the older stages did, with the juvenile and adults moving through a greater depth range than the younger furcilia stages. The data are discussed with reference to previous depth records from work carried out mainly in the Atlantic Ocean, and specifically to records from local waters.