| Both dredging for sand and fisheries with trawlers or other means for bottom-dwelling fish and shell fish such as cockles and mussels leads to substantial physical disturbance of the sea floor. Intertidal cockle exploitation in the Dutch Wadden Sea, for example, has led to serious debate on the balance between economic profit and conservation of nature and policy measures by the Dutch government .
Consensus exists that over-exploitative fisheries are causing a change in the ecosystem composition of the north-east Atlantic Ocean, and the Mediterranean and Black Sea suggesting that fish stocks are being exploited at unsustainable rates (e.g. Frid et al., 2000; Trent & Nixon, 2003). These changes involve communities of open water and bottom fish (e.g. Frid et al., 2000) as well as bottom invertebrates (e.g. Collie et al., 2000). For shallow and intertidal systems, extensive studies in the Netherlands' Wadden Sea (Leopold et al., 2004) largely confirm findings elsewhere: shellfish densities decline as well as those of larger polychaete infauna in favour of smaller, shorter-lived worms (cf Ferns et al., 2000). However, Leopold et al. (2004) could not find serious effects on sediment composition and had to cope with major temporal and apparently random variability. In addition, this is thought to have reduced the food availability to migrant wader birds as well as eider ducks, and hence their survival.
In short, trawling of the sea floor forms a major disturbance that affects biodiversity and foodweb composition.
Polychaete
A marine worm with paired, flattened, bristle-tipped organs of locomotion.
See Glossary for a complete list of all terms |
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