Determination of species of the genus Ceratium is very difficult due to the strong variability of all parts of the cell, seasonal and local variations that are observed in the size and shape of the body, when discarding or lengthening the "horns". Based on the characteristic features of the species, the taxon was identified as Ceratium tripos var. balticum F.Schutt 1895.
During more than a century of research on the phytoplankton of the Caspian Sea, the introduction of the large-celled diatom Pseudosolenia calcar-avis (=Rhizosolenia calcar-avis) was already noted in 1934. Its mass development and rapid spread throughout the entire Caspian Sea in a short time led to the displacement of previously dominant local small-celled algae species, including those that predominated in phytoplankton and were important food objects for zooplankton. The large size allowed the invader to avoid being eaten by zooplankton, while the pressure of grazing on the native small-celled algae increased. Until now, there is no effective consumer for P. calcar-avis among zooplankton organisms.
Ceratium tripos var. balticum is larger than the previously introduced P. calcar-avis, which may lead to a further reduction in the available food phytoplankton for zooplankton, and to a reduction in the biomass of zooplankton, which is the main food for Caspian sprats. Presumably, as is observed for P. calcar-avis, due to its size, C. tripos var. balticum will be included in food chains only after dying, as detritus.
The biomass and abundance indicators of the new species in the samples indicate its explosive spread, which may threaten serious structural changes in the Caspian Sea ecosystem and negatively affect productivity.
In recent years, the number of invasive species detected in the Caspian Sea has increased sharply, which may be associated with the expansion of the penetration routes of alien species into the basin and climate change processes.
VNIRO Press Service