Coccolithophorids in the Black Sea: Their interannual and long-term changes |
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| Authors: | A S Mikaelyan V A Silkin L A Pautova |
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| Institution: | 1.Shirshov Institute of Oceanology,Russian Academy of Sciences,Moscow,Russia |
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| Abstract: | A five-year study of the interannual changes observed in May–June during the mass reproduction of coccolithophorids was carried
out in the northeastern part of the Black Sea. The long-term dynamics were analyzed using the data on the phytoplankton collected
during the last 40 years. The fraction of coccolithophorids represents either 20 or 60% of the total biomass of the algae
and does not depend on either the previous winter conditions or the nitrogen content and the N: P ratio in the surface water
layer. Our studies have revealed the dependency between the phosphate content and the size of the coccolythophorids’ fraction
in the total phytoplankton biomass. The long-term population dynamics includes three periods. Until the mideighties, the coccolythophorid
fraction in the Black Sea phytoplankton was insignificant (3%). The average biomass was equal to 8 μg/l. In the late eighties,
the average biomass increased up to 106 μg/l. Since the midnineties, coccolythophorids often prevail in the number and mass
among the other phytoplankton species. The general tendency for the growth of the coccolythophorid fraction in the phytoplankton
cenoses coincides with the increase in the phosphate concentration in the near-surface water observed within the last 40 years.
This fact corresponds to the experimental results, which demonstrate that the coccolythophorid development during May–June
is phosphate-limited. |
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