Hyperscums and the population dynamics of Microcystis aeruginosa
1990; Oxford University Press; Volume: 12; Issue: 2 Linguagem: Inglês
10.1093/plankt/12.2.423
ISSN1464-3774
AutoresTamar Zohary, Richard D. Robarts,
Tópico(s)Aquatic Ecosystems and Biodiversity
ResumoConceptual models, based on 7 years of data, are constructed to simulate the annual cycle and population dynamics of Microcystis aeruginosa in hypertrophic, warm monomictic Hartbees-poort Dam, South Africa in order to assess the role of hyperscum formation. In Hartbeespoort Dam the large summer planktonic population (mean epilimnion biovolumes of 20–50 mm 3 I −1 ) and the low wind speed resulted in the formation of hyperscums (thick, crusted accumulations of floating cyanobacteria at wind-protected sites) containing up to 50% of the total standing crop for 2–3 months in 4 out of 5 years. In years in which hyperscums formed the post-maximal summer population maintained itself throughout autumn and into late winter before declining to the annual nadir (>1000 cells ml −1 ). When hyperscums did not form, or were artificially removed, the population fell to similarly low levels as early as May (autumn) and remained small until the spring growth phase began. Microcystis cells decompose in the upper layers of a hyperscum, but this is not a major loss to the planktonic population. Hyperscums are refuges which help maintain large planktonic standing crops during winter when growth is not possible but have no effect on the long-term (perennial) survival of Microcystis .
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