New Zealand Journal of Marine and Freshwater Research abstracts
SEASONAL SUCCESSION AND VERTICAL DISTRIBUTION OF PHYTOPLANKTON IN LAKE HAYES AND LAKE JOHNSON, SOUTH ISLAND, NEW ZEALAND
Carolyn W. Burns
S. F. Mitchell
Department of Zoology, University of Otago, Dunedin, New Zealand
Abstract
In two small monomictic lakes near Queenstown, South Island, New Zealand, algal associations characteristic of eutrophic waters were present throughout most of the period from December 1969 to February 1972,
In Lake Hayes, five of the six algal genera which were recorded in the plankton in 1948-50 were still present, but
Anabaena appeared to have increased. Blooms of
A. flos-aquae which were not recorded 20 y ago (Jolly 1952) occurred in the lake in the three summers of this study and in winter of the second year.
Melosira granulata dominated the plankton in winter; at other times of the year
Closterium aciculare, Cyclotella kuetzingiana, and
Staurastrum spp. were dominant.
In Lake Johnson the major algae differed from one year to another. Blooms of
Anabaena flos-aquae formed during the first two summers but were absent in the third, when
Closterium aculum var.
variabile was dominant.
Peridinium cinctum was abundant throughout the first year, especially in December 1969 and October 1970, when concentrations of more than 1000 cells per ml occurred at the surface. During autumn and winter of the second year,
Staurastrum bibrachiatum dominated the plankton.
In both lakes micro-algae were abundant in late spring and early summer.
In winter when the lakes were isothermal, algae were distributed fairly uniformly with depth. During the period of thermal stratification, algae were mainly confined to the epilimnion. Although green algae and diatoms were usually dispersed fairly uniformly throughout this zone,
Cryptomonas and
Peridinium were often concentrated at a certain depth. In Lake Johnson in late summer 1971, a layer of purple photosynthetic bacteria, of which concentrations of 0.5-1.3 X 10° cells per ml were recorded, was present at a depth of 7-8 m.
Algae were more abundant in summer than in winter in both lakes. The mean standing crop of algae for the trophogenic zone of Lake Hayes was 6000 cells per ml, and a maximum crop of 65 000 cells per ml was recorded in December 1971 during an
Anabaena bloom: the mean volume of phytoplankton was 1.93 mm
8 per litre for the trophogenic zone with a maximum of 7.49 mm
3 per litre in January 1970 when
Anabaena and
Peridinium were abundant. In Lake Johnson the mean number of algae in the trophogenic zone was 11000 cells per ml and the mean volume of phytoplankton was 9.37 mm
11 per litre: a maximum volume of 33.12mm
3 per litre was recorded in October 1970 when
Peridinium was abundant.
N.Z. Journal of Marine and Freshwater Research 8 (1): 167-209
Received for publication 7 May 1973
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