Development of Human Impact on Suspension-Feeding Bivalves in Coastal Soft-Bottom Ecosystems

Abstract

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