Long-term changes in the western Dutch Wadden Sea food web and the impact of invasive species

Abstract

This study identifies the effects of the invasions of the Pacific oyster, the American razor clam and the red-gilled mudworm on the trophic interactions within food webs of the tidal flats such as carbon flows and prey-predator interactions. In addition to the invasions, however, the Balgzand tidal flats (western Wadden Sea) experienced several other long-term changes in different components of the food web, including changes in riverine nutrient supply, in temperatures and in the occurrence of other inhabitants of the tidal flats such as bottom-dwelling fish and shrimps. This thesis describes how these concurrent changes within the system might have influenced each other. At one hand, for example, the American razor clam became a very important grazer of phytoplankton during its peak in biomass thereby enhancing the input of carbon into the local food web. Because this bivalve was difficult to access by birds, however, the additional carbon was not transferred to the rest of the food web. At the other hand, changes in factors such as salinity, nutrient availability and temperature played a role in shaping the Balgzand ecosystem and subsequently the potential of new species to become invasive. In the light of climate change, the tolerance of estuarine species towards higher temperatures and new dynamics in river runoff will become more and more important in determining who will be the winners and losers in the decades to come. This might induce shifts in present estuarine communities and, potentially, enable newly introduced species to become rapidly invasive.