New Zealand Journal of Marine and Freshwater Research abstracts

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Distribution of zooplankton in the Avon-Heath cote Estuary, Christchurch

D. S. ROPER

M. J. SIMONS*

M. B. JONES&

Department of Zoology University of Canterbury Christchurch, 1, New Zealand

Abstract Zooplankton of the Avon-Heathcote Estuary (43°33'S, 172°44'E), Christchurch, was studied at approximately 2-weekly intervals for 6 months over the autumn-winter period. Samples were collected at high tide during the day at 5 stations distributed from the northern head to the estuary mouth. During the sampling period, water temperature varied between 8.0 and 20.5°C, salinity between S=2.0 and S=33.5, and suspended matter between 2.9 and 36.8 mgL"¹. Ninety-three taxa were identified; most were coastal, marine plank-ters. Estuarine species included the copepods Gladioferens pectinatus and Halicyclops neglectus, and the ostracods Leptocythere spp. andPropontocyp-ris sp. Two species of rotifer and 6 cladocerans of freshwater origin were found also. Marine species were generally most abundant towards the mouth of the estuary, and estuarine and freshwater species were commonest towards the estuary head. Zooplankton composition at any position within the estuary was not influenced by turbidity, but reflected the degree of mixing of coastal water, fresh water, and residual estuarine water. Some organisms showed evidence of seasonality, but for most, numbers fluctuated markedly between fortnightly samples with no indication of any seasonal patterns. The data confirm the variable nature of estuarine plankton reported elsewhere.

Keywords zooplankton; estuaries; community composition; spatial distribution; salinity; temporal distribution; New Zealand east coast

New Zealand Journal of Marine and Freshwater Research, 1983, Vol. 17 : 267-278 0028-8330/83/1703-0267$2.50/0 © Crown copyright 1983 Received 25 January 1983

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