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Zooplankton of Wellington Harbour, New Zealand
The Stations
The Stations
Location
Two adjacent bays in Wellington Harbour were selected as research stations. Station One extends from Point Halswell south-east across Kau Bay to Kau Point in a zone approximately 300 yards wide (Text-fig. 2). Station Two extends Station One from Kau Point south across Mahanga Bay to Point Gordon and is approximately 200 yards wide (Text-fig. 2).
Surrounding Shores and Sea Floor
The littoral zone of both stations (Kau Bay and Mahanga Bay) consists mainly of rough shingle interspersed with rocks, but large rock outcrops extend to well below the low water mark at Point Halswell, Kau Point, and Point Gordon. From the low water mark to a depth of approximately one fathom there are extensive colonies of Macrocystis pyrifera (L.) and other algae clinging to a rocky substrate. Macrocystis pyrifera is concentrated mainly at Point Gordon, Kau Point and in Kau Bay. From one fathom to approximately five fathoms the sea floor shelves steeply, and is covered with coarse sand and gravel on which thick patches of red-green algae and large sponges grow. The sand and gravel merges into soft grey mud below five fathoms. Both plankton stations lie for the most part over the muddy substrate at depths between seven and nine fathoms.
Hydrography
Wind Influence
Station One is directly exposed to the prevailing northerly winds. Tows were not usually attempted in winds from this quarter above force four on the Beaufort Scale. Station One is however sheltered by steep hills from the less frequent southerly winds. Station Two is also exposed to the north, but its northern end is sheltered by the rocks of Kau Point.
Tidal Currents
The tidal flow pattern for Wellington Harbour has been outlined by Brodie (1958, p. 701, fig. 2). He shows that the tide floods in through the restricted harbour entrance channel at a speed of approximately ½ knot, but slows to ¼ knot in the inner harbour. The main current passes close to Seatoun, Mahanga Bay, and Point Halswell, and continues in a clockwise direction parallel to the inner harbour coastline to follow a southerly course along the eastern harbour bays to Eastbourne. This pattern of flow is reversed during the ebb tide. Both plankton stations are therefore influenced by oceanic waters during the flood tide only, and during the ebb tide a flow from the northern inner harbour mixed with water from Evans Bay covers the area.
Fresh Water Influence
With heavy flooding in the Hutt River and the Kaiwharawhara and Ngauranga streams the plankton stations were discoloured by muddy water. Under such conditions no significant change was seen in the plankton samples.
Pollution
Effluence from the Ngauranga Freezing Works appeared to have no marked effect on the plankton samples. Effluence was mainly particles of fat which surface drifted in the direction of the stations during prolonged wind from a northerly quarter.
Surface Water Temperatures
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Text-fig. 2.—Location map of Wellington Harbour. Showing the harbour plankton research stations.
seen (Text-fig. 8). Highest temperatures, above 18.0°C., were recorded in February of each year, and the coolest months were July and August when temperatures below 10.0°C. were recorded. The highest temperature recorded was 20.0°C. on 1 February 1962, and the lowest temperature was 8.8°C. on 11 August 1961.Mean monthly surface water temperatures varied from year to year. This variation was due to the difference in air temperatures as shown by the meteorological records. Thus the milder winter of 1962 kept the mean water temperature above that of 1961 and 1963 by approximately 2°C. (Text-fig. 8). Short period temperature fluctuations of 3°C. or 4°C. were recorded mainly in winter during calm weather and in midsummer after cold southerly rain.