New Zealand Journal of Marine and Freshwater Research abstracts

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Phytoplankton species of Lake Okaro, Central North Island

SUSAN J. DRYDEN WARWICK F. VINCENT

Taupo Research Laboratory
Division of Marine and Freshwater Science
Department of Scientific and Industrial Research
P. O. Box 415, Taupo
New Zealand

Abstract The species composition of the Lake Okaro (New Zealand) phytoplankton community was described as part of a detailed study of the lake ecosystem during 1979/80. The dimensions of each species were measured to estimate cell biovolume and to define the morphometric characteristics of each population. The algal dominants (> 50% of community biomass) were bloom-forming cyano-phytes in summer through to early winter (Micro-cyst is aeruginosa Kiitz., Anabaena flos-aquae (Lyng.) Breb., A. spiroides Kleb.), centric diatoms in autumn and winter (Melosira granulata (Ehr.) Ralfs, M. granulata var. angustissima Mull.), and colonial chlorococcaleans in spring (Coelastrum microporum Naegeli, Micractinium pusiltum Fre-senius, Oocystis parva West and West, Actinastrum hantzschii Lagerh.). These algal communities were different to the communities recorded in Lake Okaro 10 years earlier. M. granulata dominated the winter plankton in 1980 but not 1970. Colonial chlorococcaleans were more important constituents throughout the year than during 1970, and a previously unrecorded, non N₂-fixing blue-green alga (M. aeruginosa) produced water blooms from December 1979 to June 1980. The chlorococcalean and cyanophyte shifts suggest that further enrichment of this eutrophic water body has occurred over the decade 1970-80.

New Zealand Journal of Marine and Freshwater Research, 1986, Vol. 20: 191-198 Received 29 April 1985; accepted 26 July 1985

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