New Zealand Journal of Marine and Freshwater Research abstracts

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Role of microzooplankton grazers in the subtropical and subantarctic waters to the east of New Zealand

Julie Hall
Karl Safi
Andrea Cumming

National Institute of Water and Atmospheric
 Research Limited
P.O. Box 11 115
Hamilton, New Zealand
email: j.hall@niwa.co.nz

Abstract  Subtropical and subantarctic surface waters to the east of New Zealand were sampled in four seasons over a period of 3 years to evaluate the importance of the microzooplankton as grazers of the phytoplankton community. Subtropical waters (STW) to the north were warm with high salinity and seasonal macronutrient limitation. Subantarctic waters (SAW) to the south were colder, with lower salinity, high macronutrient concentrations and chlorophyll a concentrations between 0.20 and 0.28 μg litre^-1. In the STW, phytoplankton showed a typical seasonal pattern for macronutrient-limited waters, with biomass dominated by large phytoplankton and a chlorophyll a maximum of 1.4 μg litre^-1 in spring. Microzooplankton biomass varied from 4.5 μg carbon (C) litre^-1 in the STW in winter, to 13.8 μg C litre^-1 in the SAW in winter with the heterotrophic flagellates contributing between 22% and 78% of the biomass. In spring and winter in the STW, only 73% of the primary production was grazed by the microzooplankton compared with over 100% in autumn and summer. In contrast, over 100% of the primary production was consumed in all seasons by the microzooplankton in SAW. In the SAW in all seasons and the STW in summer and autumn, microzooplankton grazing on phytoplankton dominated the organic matter fluxes from the phytoplankton population. During these periods the picophytoplankton contributed a significant proportion of the phytoplankton biomass.

Keywords  picophytoplankton; phytoplankton; microzooplankton; grazing

M02069; Online publication date 15 March 2004; Received 2 September 2002; accepted 25 November 2003
New Zealand Journal of Marine and Freshwater Research, 2004, Vol. 38: 91-101
0028-8330/04/3801-0091 © The Royal Society of New Zealand 2004

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