engleski

Temporal and Vertical Distribution of Phytoplankton in Rogoznica Lake

Microplankton in the small, naturally eutrophic and periodically anoxic marine Lake Rogoznica (eastern Adriatic coast) was investigated in the period from October 1995 to December 2002. Microphytoplankton distribution in the water collumn reveals unexpected development of dinoflagellate species in upper water layer in February, possibly due to the winter resuspension of organic material. In the rest of the year, diatomes prevailed in upper layer, while dinofllagelates accumulated in the deeper layer of the water column, around and under the picnocline. The research provided evidence of exceptionally dense populations and the seasonal recurrent appearance of one diatom species Cheatoceros curvisetus followed by two microflagellates: Prorocentrum arcuatum Issel. (mixotrophic dinoflagellate) and Hermesinum adriaticum (heterotrophic microflagellate of uncertain taxonomic position). The development of these species, usually rare in marine environments, is mostly regulated by temperature (i.e. temperature dependant factors). Hermesinum adriaticum and P. arcuatum mostly appeared in summer during nitrate deficiency, while C. curvisetus dominated in spring during more favorable nitrate concentrations. Such seasonality was absent only during pre– anoxia and post– anoxia period (following October 15 1997). In the post-anoxia period P. arcuatum developed first in succession, probably due to it’ s possibility to form cysts witch are capable of surviving anoxic conditions.

anoxia; phytoplankton; Rogoznica Lake; seasonality

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