Seasonal variations in length of copepods in South Pacific New Zealand waters

Abstract

Measurements of cephalothorax length were made on females and males of Centropages aucklandicus, Acartia clausi, Paracalanus parvus, and Clausocalanus arcuicornis, and on female Calanus australis for the period from April 1964 to May 1965. Centropages aucklandicus and A. clausi increased gradually in length during autumn and winter to maximal size in the spring and were smaller again in summer. Paracalanus parvus was larger in spring and smaller the rest of the year. Calanus australis and C. arcuicornis were large in spring, but during summer they were also large on occasion, possibly because offshore populations had been brought into the area.

Length-temperature-phytoplankton correlations showed that in temperate New Zealand waters with a relatively narrow temperature range the seasonal variations in length of all the copepods studied were significantly related to the annual phytoplankton cycle; temperature was an important factor for only two of the species. Some of the species measured are primarily herbivorous whereas others, such as Centropages and Acartia, are probably omnivores. Data are lacking for carnivorous copepods. However, since the spring bloom acts as a stimulus to zooplankton reproduction, it is suggested that all copepods that feed on living food might attain maximal size at around the time of the spring bloom in temperate waters with a relatively narrow temperature range.