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Summary
The Peridinium spring bloom in Lake Kinneret was studied by means of fluorometric and turbidometric techniques.
During the height of the bloom, Peridinium constituted 94–99 % of the total phytoplankton volume and kept close to the surface. Patches with up to 4000 cells/ml were formed. From April onwards, Peridinium retreated to deeper layers during daytime. In early morning the cells aggregated at 1.5–2 meters depth in a sharply defined peak, and some hours later a second peak was formed deeper down. Dense masses of Peridinium can be brought to the surface by upwelling water, as indicated by long and narrow brown strips which appeared in some areas shortly after the onset of strong winds. The forced exposures to intense light, together with high temperature and nutrient deficiency, may have contributed to the decline of the population in June.
Whereas the vertical distribution resulted mainly from active swimming by the cells, the strong currents of Lake Kinneret appeared to be the most important factor governing horizontal patchiness of the Peridinium bloom.
Tentative biomass calculations gave compatible results from fluorometric profiles and direct phytoplankton counts. Maximum figures of 17000–20000 tons of wet weight were obtained for the total Peridinium population of the lake (170 km2, calculated for the layer down to 10 or 12 meters depth).