MAP Technical Reports Series No. 106 UNEP

- 69 -
winter months (Del Rio et al., 1986). Balle Cruelas (1965) also reports cases of abnormal
proliferation of diatoms off the Balearic Islands. In view of the location these blooms should
probably be attributed to normal cycles of upwelling of deep waters rich in nutrients.
Lagoons, bays, estuaries. In areas such as lagoons and estuaries where primary
productivity is generally high, increased supply of eutrophying substances of human origin has
been raising the trophic level to worrying levels over recent years. In areas of reduced water
exchange this condition generates significant levels of dystrophy and states of hypoxia/anoxia
(Lopez and Arte, 1971). Cases have been reported by Miracle et al. (1988) in the Albufera of
Valencia; this lagoon (area 26 km 2 ; mean depth of 1.1 m) receives an influx of nutrients
equivalent to 2.077 tons of nitrate+nitrite nitrogen, 1.908 of ammoniacal nitrogen, and 619 tons
of phosphorus every year (Vicente et al., 1990). Other cases are reported for the lagoons of
Encanizada, Platjola and Olles in the Ebro delta by Comin (1986), and for the Lagoon of Cadice
in the Guadalquivir delta to the West of the Strait of Gibraltar. Some of these areas are of
particular interest to naturalists because of the birds that winter and breed there. Amongst such
zones, Cruzado (1990) mentions the Alguamoles of the Ampurda, the lagoons along the coast
of Valencia, the Menor Sea and the Guadalquivir estuary system.
Even if the connection with eutrophication is doubtful, blooms of planktonic and nectonic
organisms consisting of Salpae, jelly-fish and Noctiluca miliaris have been observed in various
areas of the Southern coast of Spain. Early in 1986, a microalgae bloom which originated in the
Bay of Rosas affected 120 km of coastline (Cruzado, 1989).
5.2.2 France: North-western Mediterranean
General situation regarding eutrophication along French coasts. Areas affected along
the Atlantic French coast are mainly subject to excessive proliferation of macroalgae (Ulvaceae,
particularly in the lagoons and in some Breton bays) and to phytoplankton blooms in the areas
adjoining the estuaries of the major rivers. During the last twenty years these phenomena have
gradually increased, in direct correlation with the increased presence of eutrophying substances
of human origin. Naturally, the areas most affected are those with the longest water residence
times, and those which receive water from river basins with large populations and/or from urban
agglomerations along the coast (Ménesguen, 1990).
The excessive proliferation of macroalgae has created fairly significant environmental
dystrophies (summer anoxia in the lagoons and bays, production of volatile substances such
as hydrogen sulphide and large accumulations of phyto-biomass) generating serious economic
problems for the local authorities, which have had to remove the masses of Ulvaceae from the
beaches (Piriou, 1986). Along the coasts of Britany from 1985 to 1988 the total cost of collecting
these biomasses rose from 1.6 to 2.5 million francs (CEVA, 1989).
Also, abnormal proliferations of microalgae seem to be more significant and
widespread in the northern and Atlantic coasts than on the Mediterranean coast. During 1975-
1988 Belin et al. (1989) recorded 62 cases on France's northern coast, 125 on the Atlantic and
26 on the Mediterranean (Fig. 10). In general the organisms which have led to "coloured water"
are dinoflagellates of the species Noctiluca scintillans, Prorocentrum minimum, Gonyaulax sp.,
Gyrodinium aureolum and Gymnodinium sp.. From an overall analysis of the events which have
occurred in the North Sea, it appears that in many cases flagellates have acquired dominance
over diatoms during the last 20 years (Radach and Berg, 1986). The algal blooms observed
during the period 1975-1988 showed a constant increase until 1984, after which there was a
reduction in events that in numerical terms settled around values comparable to those of 1982-
83.