MAP Technical Reports Series No. 106 UNEP

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Bay of Thessaloniki (north-west of the Gulf of Thermaikos). A eutrophic situation similar
to that in the Bay of Elefsis and the Gulf of Amvrakikos (Balopoulos and Friligos, 1986;
Samanidou et al., 1986). Huge amounts of nutrients are carried into this Gulf by industrial
effluents and the sewage outfalls of the city of Thessaloniki (population 1,300,000) and the
waters of four rivers. The Axios river is held responsible for transferring large quantities of
nitrates of agricultural origin into the Gulf. In this zone, the increase in the phytoplankton biomass
is directly correlated with the increases in nitrates and phosphates and with the reduction in
salinity values. The blooms are generally caused by diatoms: Nitzschia closterium, Cerataulina
bergonii, Leptocylindrus minimus, Chaetoceros socialis and Thalassiosira sp. are the dominant
species in the majority of cases (Gotsis-Skretas and Friligos, 1988).
Gulf of Kavala. Although the trophic levels are generally lower than in the other areas
mentioned, it appears that a bloom of the dinoflagellate Gonyaulax polyedra with 10,000,000
cells/l that occurred in August 1986 in the north-western part of the Gulf was caused by the
wrecking of a ship transporting phosphate fertilizers (Panagiotides et al., 1989).
Estuary of the Vistonis River. Yiannakopoulou (1992) reports an intense bloom in
August 1984 with maximum chlorophyll-a values of 86.0 mg/m 3 , consisting mainly of
cyanobacteria.
Gulf of Alexandropoulis (to the North-East of the Aegean). A trophic situation similar to
Kavala. Mainly because of the emissions of the Evros river, in 1981-1982 concentrations of
silicates and nitrates were three times and six times respectively higher than normal (Pagou,
1990).
5.2.7 Malta: Central Mediterranean
A three year monitoring program (1989-1991) was carried out in Malta in order to define
the trophic state of two intensely urbanized port areas with heavy commercial traffic, the Grand
Harbour and the Marsamxett Harbour. Axiak et al. (1992) found that the nutrient and chlorophyll
levels were comparable to those measured in other areas of the Mediterranean where clear
signs of eutrophication already exist. Increased levels of primary productivity has reduced the
transparency of the waters, particularly in the innermost areas with the longest water residence
times, showing a mean of 2.6 m. The same areas have the highest mean values of nutrients
(26.4 and 1.6 mg-at/m 3 for nitrates and orthophosphate, respectively) and chlorophyll-a. Nutrient
inputs come above all from sewage outfalls (population of 73,000 in the capital Valletta and its
suburbs), although the contribution of shipping and tourism should also be mentioned.
5.2.8 Turkey: North-eastern Mediterranean
Open marine waters of Turkey generally present conditions of oligotrophy; only in
limited costal areas affected by the inputs of rivers, sewage outfalls or industrial effluents
conditions of eutrophy are reported.
The Sea of Marmara is an exception because of both its size, hydrology and
hydrodynamics. A semi-enclosed sea, with an area of 11,500 km 2 and a volume of 3,378 km 3 ,
its dominant low-density surface current tends to flow from East to West, while the bottom
current carries high-density Mediterranean water from the Dardanelles towards the Bosphorus.
During an oceanographic cruise in the Sea of Marmara from 30 June to 8 July 1990, Aubert et
al. (1990) measured particularly high orthophosphate and inorganic nitrogen