The State of the Mediterranean Marine and Coastal Environment

account for 70–90 % of the total abundance (Stergiou et al. 1997). The same applies to the Western Mediterranean benthic com- munities, where increasing disturbance also leads to reduction in species richness. When the effects from organic enrichment exceed the potential for remineralisation (transforming the organic matter into in­ organic matter) by benthic organisms, anoxic zones are created and bacterial mats cover the seabed. Although this type of eco- system change is in general reversible, there could be severe and long-lasting consequences when the affected seabed is a criti- cal habitat like the meadows of the sea grass Posidonia oceanica (UNEP/MAP/MED POL 2005). Heavy metals The term heavy metal is used here for potentially toxic metals that persist in the environment, bioaccumulate in human and animal tissues, and biomagnify in food chains. Metals and orga- nometallic compounds are commonly included in emission in- ventories and monitoring networks, specially mercury, cadmium

Composition of benthic communities Co position of benthic co unities

Crustacea Echinodermata Miscellaneous Crustacea Echinodermata Miscellaneous

Polychaeta Mollusca Polychaeta Mollusca

Undisturbed area Source: ETC/MCE compilation, data from NCMR. Undisturbed area Source: ETC/MCE compilation, data from NCMR.

Polluted area Polluted area

their loss is a liability to the ecosystem as a whole. In undisturbed areas in the eastern Mediterranean, benthic communities have a high diversity of species, consisting of polychaetes (50–65%), molluscs (15–25 %), crustaceans (10–20 %), echinoderms (5–8 %) and miscellaneous taxa. By contrast, in areas ranging from heav- ily disturbed (e.g., sewage outfall vicinity) to polluted (e.g., ur- banised bay), echinoderms, crustaceans and miscellaneous taxa largely disappear, while a small number of polychaete species

Mean concentrations of trace metals

In Blue Mussels ( Mytilus galloprovincialis )

In sediments

Lead

PCB

Lead

Up to 20 21 to 46 47 to 218 219 to 370 Concentration, μg/g dw

Concentration, μg/g dw

Co

Up to 1.56 1.57 to 3.74

3.75 to 8.15 8.16 to 28.05

Mercury

DD

Mercury

Concentration, μg/g dw

Co

Concentration, μg/g dw

Up to 0.15 0.16 to 0.75

0.76 to 7.5

Up to 0.01 0.23to 0.53

0.02 to 0.22

7.6 to 81.3

0.53 to 3.69

Cadmium

H

Cadmium

Co

Concentration, μg/g dw

Concentration, μg/g dw

Up to 0.6 0.7 to 2.0

2.1 to 4.5

Up to 0.80 0.81 to 1.15

1.16 to 2.00

4.6 to 64.1

2.01 to 3.91

Source: U

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STATE OF THE MEDITERRANEAN MARINE AND COASTAL ENVIRONMENT