Diatoms from the sewage discharge area on the shelf of the Black Sea  <B>Diatoms from the sewage discharge area on the shelf of the Black Sea</B><P>L.G. Senichkina</B><I><P> Plankton Department, Institute of Biology of the Southern Seas, National Academy of Sciences of Ukraine, Crimea, Ukraine</I><P> Abstract<P> The impact of urban sewage upon diatom algae has been studied for three years (February 1987March 1990) at a testing area on the Black Sea shelf adjoining the western coast of the Crimea. Samples have been taken monthly from sea surface above the sewage discharge outlet, in waters polluted with sewage effluent and in unpolluted sea area regarded as a check (control site).<P> Diatoms totalled 60 species. 3440 species have been recorded annually that averaged 4243 % of the total number of phytoplankton species. Diatoms common to the northern shelf of the Black Sea prevailed, half of them were all the yearround species. Only four mass species have been found any time of a year, the largecelled Rhizosolenia calcar avis Schultze and Cerataulina bergonii Perag. and the smallcelled chainlike Sceletonema costatum (Grev.) Cl. and Pseudonitzschia delicatissima Cl. These diatoms induced phytoplankton blooms along the testing area at different seasons.<P> Absolute values of the numbers and biomass varying, the share contributed by diatoms into the total numbers of phytoplankton averaged 3844 % and into the total biomass 4356 %. The abundance of diatoms in general and of the mass species in particular varied depending on season and the extend of pollution.<P>