Nutrient pollution. The Black Sea is utterly polluted by organic matter and inorganic nutrients originating from agriculture, animal husbandry, domestic and industrial sewage, etc. The excessive loading of sea water with nitrogen- and phosphorus-containing substances is considered as a primary cause of the decline of the shelf ecosystems (Zaitsev, 1993; Mee and Topping, 1999) which are crowned by inshore top predators including bottlenose dolphins. A large share of nutrients is contributed to the sea by rivers. The peak of nutrient inputs has been observed in the 1970s and 1980s (Xxxxxxx and Xxxxxx, 1997). Huge inputs of nutrients are causing the eutrophication of shallow waters mainly in the northwestern Black Sea shelf area. This phenomenon includes the production of algal and zooplanktonic blooms; decline of water transparency; oxygen deficiency in the near-bottom water layer; disappearance of benthic phytocenoses at a depth below 10 m; mass mortalities of benthic fishes and invertebrates with associated widespread decay of their remains and seaweed residues (Xxxxxxx and Xxxxxx, 1997). Fish mass mortality events occur in the Black Sea since the late 1960s; blooms of dinoflagellates became annual since the early 1970s. The areas of eutrophication in the northwestern Black Sea expanded from 3,500 km2 in 1973 to 40,000 km2 in 1990 (Zaitsev, 1993). Finally, the “hyperfertilization” of sea water has resulted in widespread decline of biodiversity (Xxxxxxx, 1999). The assumed cetaceans-applied effects of the nutrient pollution include the diminution of forage areas and the depletion of benthic food resources. Both these effects could be stressful for bottlenose dolphins which consume benthic fishes. Besides, the fertilized water represents a growth medium for potentially pathogenic bacteria (see 7.2.1.7 and 7.6.2) and for toxin-producing planktonic species whose toxins may be accumulated in cetacean prey.
