MAP Technical Reports Series No. 106 UNEP

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waters (eg Pojed and Kveder, 1977; Smodlaka, 1986; Degobbis, 1990b). In conclusion, oxygen
changes in the northern Adriatic may not necessarily depend on eutrophication, especially in
periods when unusual meteorological processes significantly affect the water exchange rate
between the northern and central Adriatic. According to Degobbis et al. (in press) eutrophication
trends inferred from oxygen only (eg. Justic et al., 1987), should be re-evaluated.
It further appears that water transparency in the northern Adriatic has also been
significantly decreasing over time with a gradual increase in suspended organic particles
(phytoplankton biomass and debris). Compared to data obtained in the period 1911-1913 with
those form 1972-1982 (Justic, 1988) transparency in the western part of the northern Adriatic
has fallen by 1/3. Domijan and Smircic (1992) reach the same conclusions: decrease of
transparency measured in the entire basin in different periods (1956-1971 compared with 1972-
1990) was estimated at 1/3 in the northern Adriatic and at about 1/5 in the central and southern
Adriatic.
The orography of the eastern Adriatic basin and its coasts (the former Yugoslavia) is
generally mountainous that prevents the transfer to the sea of waters from large internal
hydrographic basins. Therefore, and in contrast with the north-western nearshore waters,
eutrophication phenomena which occur in the coastal waters of the easter Adriatic are normally
of a local nature. In almost all cases, the zones affected by the phenomena are the ports and
bays, whose trophic state is influenced by sewage outfalls and industrial effluents.
Bay of Pula. Because of the inadequacy of the sewage treatment system, during the
last 20 years this area has gradually deteriorated (Maretic et al., 1977). Recurrent dinoflagellate
blooms may reach chlorophyll-a concentrations in excess of 120 mg/m 3 . Prorocentrum micans
generally causes blooms during the spring, while in the summer Gonyaulax poliedra blooms
occur; other blooms are periodically caused by Noctiluca miliaris and by the genus
Gymnodinium (Degobbis, 1990a).
Bay of Rijeka. Although oligotrophic throughout most of its area, the bay is affected by
high trophic levels in the northern part due to the input of the Rjecina river, sewage outfalls and
industrial effluents (Degobbis, 1990a).
Dalmatian coast. Recurrent eutrophic episodes are also reported from the estuary of
the Krka river, including the Bay of Sibenik. The western part of the bay is particularly affected
because of the nutrient inputs from the city of Sibenik (population 30,000) and industrial areas.
Legovic et al. (1991a; 1991b) report a bloom of Gonyaulax poliedra in the centre of the bay in
October 1988. This event, associated with inputs of nutrients, heavy rainfall and a marked
halocline, caused anoxia in the bottom waters with widespread bottom fauna kills.
A research project lasting 14 years aimed at identifying the physical-chemical and
biological characteristics of a vast area off the main cities of Dalmatia (Zadar, Sibenik, Split,
Ploce and Dubrovnik), by Pucher-Petkovic and Marasovic (1992) show blooms in the Bay of
Sibenik normally caused by dinoflagellates. They also report large increases in nitrogen
(particularly nitrates) during the last few years.
Bay of Kastela. There are many reports of blooms in the bay on which the city of Split
stands. Marasovic (1986; 1989; 1990), Marasovic et al. (1991) and Gacic et al. (1988) highlight
that recurrent algal blooms are coincident with the growing input of fertilizing substances.
Primary productivity has risen from 120 gC m 2 /year in 1963 to 250 gC m 2 /year