Development of human impact on suspension-feeding bivalves in coastal soft-bottom ecosystems

Suspension-feeding bivalves often may occur in large concentrations ('beds') on tidal flats. This makes them attractive for human consumers and the archaeological record shows collection of bivalves by coastal populations already tens of thousands of years ago. In modem time human interference with coastal stocks of bivalves intensified. This paper describes the successive steps in this development: 1. Local exploitation and local consumption, leading to reduction of average age, average size and small shifts in species composition. 2. Local exploitation coupled to remote markets. This leads to the same changes as at 1, but also may lead to extirpation of local populations. 3. Relaying of imported bivalves to restock overexploited beds. This may result in destruction of genetic adaptations, and it has been demonstrated that it results in the importation of parasites and diseases. 4. Cultivation of bivalves with either spat from natural sources or from hatcheries. Bivalve culture usually results in increased harvests compared to open fisheries; it may lead to overstocking with effects on the remainder of the ecosystem. 5. Introduction of new, exotic species, either to be cultivated or as an unplanned introduction of 'weed' species.