| Popis: |
The red tide flagellates, Heterosigma cf. akashiwo Hada (Raphidophyceae) and Gymnodinium cf. mikimotoi Miyake et Kominami (Dinophyceae), which have well-known ichthyotoxic effects, have been recorded for the first time in Izmir Bay, Turkey. They were particularly abundant in the hypereutrophic Inner Bay and the eutrophic Middle Bay in September and November 1998. In the Inner Bay, the maximum cell density of H. akashiwo was 222,300 cells/l and that of G. mikimotoi was 15,900 cells/l on 2 September 1998. Water quality and meteorological conditions measured and/or recorded during this period are discussed in relation to phytoplankton proliferations. The reported environmental conditions that enhance the growth of these two species (i.e., phosphate, nitrogen, and iron enrichments; temperature; and salinity) have been reconfirmed. Since there has been a monitoring program in Izmir Bay for more than 20 years, and both species are cyst-forming organisms with rapid reproduction and mortality properties, it is likely that they have occurred much earlier than when this study was carried out. The cyst-forming ability of these species suggests that their introduction into the bay might be via ballast waters of long-distance cargo ships. Finally, the sediment-dredging activity being carried out at irregular intervals in the bay could be considered a potential mechanical factor that favors the growth and reproduction of these species. |
