Ecosystem dynamics across trophic levels Most susceptible to the negative impacts of eutrophication are semi-enclosed basins, estuaries, and lagoons, where excess nu- trients are not easily dispersed (UNEP/MAP/MED POL 2005).
Red tides are a problem for some Mediterranean fisheries. Fish- ing and mollusc farming in the northwestern Adriatic have been damaged by blooms of the dinoflagellate, Dinophysis spp., which causes Diarrhoetic Shellfish Poisoning (DSP). The occurrence of this organism has been responsible for temporary and pro- longed bans on the harvesting and sale of mussels in the coastal and lagoon areas of Emilia-Romagna (UNEP/MAP/MED POL 2005). Alexandrium tamarensis, a dinoflagellate that produces Paralytic Shellfish Poisoning (PSP) toxins has been observed in the northern Adriatic (UNEP/MAP/MED POL 2005).
The initial Integrated Assessment data suggest that eutrophica- tion is still a localised phenomenon in the Mediterranean Basin. Better monitoring regimes and analysis of resulting data to de- termine trends will, in the future, allow robust statements of the effect of eutrophication on the ecology, as well as on fisheries and other valuable ecosystem services.
Proportion and abundance at different trophic levels
Overfishing is changing the distribution and abundance of a number of species in the Mediterranean. There is evidence that demersal, or bottom-dwelling stocks are becoming dominated by juveniles. Among the species affected are red mullet (Mullus
barbatus), striped red mullet (Mullus surmuletus), four-spotted megrim (Lepidorhombus boscii) and spotted flounder (Citharus linguatula) (EEA and UNEP 2006).
Overfishing in the Mediterranean has also caused a collapse in red coral beds (Corallium rubrum), date shell (Lithophaga lith- ophaga), some sponges, such as Hypospongia communis and some Spongia species and some Decapoda crustaceans, such as the European lobster (Homarus gammarus) and the European spiny lobster (Palinurus elephas) (UNEP/MAP 2012). Numerous fish stocks are overexploited and experiencing declines. They include the European eel (Anguilla anguilla), dusky grouper (Epinephelus marginatus), and brown meager (Sciaena umbra) (UNEP/MAP 2012). Hake (Merluccius merluccius), mullet (Mullus barbatus), deep sea pink shrimp (Parapenaeus longirostris), sole (Solea solea), sardine (Sardina pilchardus), and anchovy (Engraulis encrasicolus) are also overfished in various parts of the Mediter- ranean (UNEP/MAP 2012).
There is a particular concern with respect to the overfishing of many big pelagic species, including the Mediterranean bluefin tuna (Thunnus thynnus), swordfish (Xiphias gladius), albacore (Thunnus alalunga), and pelagic sharks, such as the blue shark (Prionace glauca) (UNEP/MAP 2012). Sharks are under particular pressure in the Mediterranean. A 2008 study of 20 shark spe- cies using records dating back to the early 19th and mid 20th century found sufficient data for only five species, and these five had all declined by more than 96 % (Ferretti et al. 2008). The decrease of top-level predators in the Mediterranean Sea is already altering marine food webs in many parts of the sea (Sala 2004).
HUMAN PRESSURE, STATE AND IMPACTS ON MEDITERRANEAN ECOSYSTEMS