Sexuality and cyst formation of the spring-bloom dinoflagellate Scrippsiella hangoei in the coastal northern Baltic Sea |
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Authors: | A Kremp A-S Heiskanen |
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Institution: | University of Helsinki, Department of Ecology and Systematics, Division of Hydrobiology, P.O. Box 17, FIN-00014 Helsinki, Finland, FI Finnish Environment Institute, P.O. Box 140, FIN-00251 Helsinki, Finland, FI
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Abstract: | The temporal sequence and the magnitude of the sexual reproduction and subsequent cyst deposition of the common spring-bloom
dinoflagellate Scrippsiella hangoei (Schiller) Larsen was studied during spring 1996 on the SW coast of Finland, Baltic Sea. The abundances of the different
size of fractions of S. hangoei (14 to 18 μm, 18 to 22 μm and >22 μm) were monitored in the water column, and the deposition of resting cysts was measured
using moored sediment traps. Cyst sedimentation rates were measured throughout the seasonal cycle in order to estimate cyst
resuspension rates for the quantitative assessment of the fraction of population undergoing encystment. The onset of sexual
reproduction, indicated by a significant increase of the small cells (14 to 18 μm) representing gametes, occurred in a nutrient
replete environment well before the exponential growth phase and peak abundances of vegetative cells. Gamete formation was
followed by high abundances of large cells (>22 μm) representing planozygotes, and subsequent sedimentation of resting cysts.
Approximately 60% of the asexually growing bloom population was estimated to form planozygotes, suggesting that encystment
was an important factor in bloom termination and possibly plays a role in the regulation of the magnitude of the bloom. Finally
encystment accounted for 40% of the entire S. hangoei population, resulting in a considerable loss of the bloom population and an input of the vernal phytoplankton biomass to
the benthos.
Received: 11 December 1998 / Accepted: 8 April 1999 |
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