Pseudosolenia calcar-avis (Bacillariophyta, Centrophyceae) in the Caspian Sea

Autor: M. G. Karpinsky
Rok vydání: 2010
Předmět:
Zdroj: Russian Journal of Biological Invasions. 1:81-86
ISSN: 2075-1125
2075-1117
DOI: 10.1134/s2075111710020050
Popis: The diatom Pseudosolenia (Rhizosolenia) calcar-avis was introduced into the Caspian Sea in 1934. Within a year, it spread throughout the water area with salinity higher than 8%o and dominated in the phy-toplankton community, constituting 80–90% of the total biomass in the Middle and Southern Caspian and 20–40% in the Northern Caspian. After this introduction, the role of small-celled diatom alga Rhizosolenia fragilissima and pyrophyte Exuviaella cordata dominating earlier decreased sharply. The first species was found in single instances; the biomass of the second one decreased substantially. The P. calcar-avis domination was observed until 2000 under all environmental changes connected with the sea level fluctuations. In 2000, small-celled algae, including R. fragilissima, began to develop intensely, and in 2001, the fraction of P. calcar-avis in the total biomass decreased to 5–10% in the Middle and Southern Caspian. This occurred after the invasion of the comb jelly Mnemiopsis leidyi, which sharply decreased the number of zooplankton phytophages and as a result reduced the rate of phytoplankton grazing. P. calcar-avis, which previously successfully competed with a native phytoplankton, owing to the fact that because of its large size zooplankton organisms did not feed on it, lost its advantageous position and small-celled algae subjected earlier to grazing pressure became dominant. The grazing pressure decrease has facilitated penetration of new phytoplankton species into the Caspian Sea. If for 70 years of the 20th century only two species penetrated into the Caspian Sea, within 9 years after the comb jelly invasion at least seven species appeared in the Caspian Sea.
Databáze: OpenAIRE
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