The Distribution and Abundance of Surface Macro-Zooplankton in the Waters off the Otago Coast

Abstract

The present study quantifies the effects of various water masses, including the oceanic, neritic, and coastal waters, on the abundance and distribution of surface macro-zooplankton off the Otago Coast through a series of coastal transects carried out in May, 2014. Three zooplankton assemblages were identified through the use of multivariate analysis: (1) the offshore Southland Current assemblage, (2) the inner Blueskin Bay assemblage, and (3) the midshelf-northern Blueskin Bay assemblage. The zooplankton components found in each assemblage were strongly related to the specific hydrology aspects of the water masses in which they were found.

In addition, the oceanography of the waters off the Otago Coast, including temperatures and salinity levels, species abundances, and zooplankton assemblages in May 2014 were compared to a study carried out by Murdoch (1989) in May 1982, using identical sampling methods and sampling locations. The mean surface temperature and salinity levels of the surface waters off the Otago Coast were significantly lower in May 2014 compared to in May 1982. The abundances of hyperiid amphipod of genus Themisto, chaetognaths Serratosagitta tasmanica, pteropods Limacina helicina, and L. inflata were found to be significantly greater in May 2014 compared to May 1982. The three zooplankton assemblages identified in the present study was consistent to that identified by Murdoch (1989), and surface water salinity levels were found to contribute to the variations in zooplankton composition between the three assemblages, more so than the temperature levels. There was also no evidence of a shift in phenology of the zooplankton assemblages in the waters off the Otago Coast.