Calanus tonsus (Copepoda, Calanoida) in southern New Zealand waters with notes on the male

Abstract

Calanus tonsus, a subantarctic planktonic copepod, was taken abundantly in surface waters off south-eastern New Zealand in spring and early summer (September to January). Nearly two generations are passed in this time but individuals of the second generation appear to descend into deep water as Stage V copepodites. Here they overwinter before they mature and breed in August. Males were not taken at all in surface samples and only appeared in deep water upon the maturation of the overwintering stocks. When they first appear, males outnumber females.

C. tonsus was seasonally abundant near the surface in the Southland Current, and further offshore in subantarctic water, but not in neritic waters near the shore. It is probably introduced into the Southland Current each spring from deeper subantarctic water.

C. tonsus is closely related to C.plumchrus of the North Pacific and the two species have many similarities in their life-cycles and hydrological afiities.

The male of C. tonsus has been more fully described in this paper.