Cook Strait chaetognatha

Abstract

Quantitative plankton sampling for chaetognaths was carried out in Cook Strait over a 17 month period. Chaetognath species present in Cook Strait were (in order of abundance) Sagitta tasmanica, S.minima, S.gazellae, Eukrohnia hamata, S.ferox, Pterosagitta draco and Krohnitta subtilis. Temperature and depth ranges for all species in Cook Strait are assessed; and seasonal distribution and water preference (oceanic or neritic) are compared with published data. The reproductive potential of S.tasmanica is discussed. The chaetognath fauna of Cook Strait reflects the subtropical and subantarctic origins of the water masses in that area. Both S.tasmanica and S.gazellae have strong subantarctic affinities, E.hamata is a cold water form, while S.ferox, P.draco and K.subtilis are subtropical forms. S.minima is seen to prefer neritic water. The distribution and abundance of each species in Cook Strait is examined, and discussion on the use of chaetognaths as indicator species presented. The possibility of using chaetognaths as indicator organisms seems restricted to examining the degree of penetration by cold and warm water masses. Comparison of the chaetognath fauna from each sample area (deep offshore, shallow inshore) enabled water mass comparisons to be made. The geographical range of each species is commented upon. Hydrological factors were found not to be important in limiting the distribution or abundance of most species found in Cook Strait. Turbulence in the area probably accounts for this. Cook Strait chaetognath populations appear to have lower temperature ranges when compared with the same species in other areas. Movements of the Subtropical Convergence in the Cook Strait area do not appear to markedly influence the dispersal of species. Species distribution is not sharply limited by temperature, although abundance declines outside the established temperature ranges.