Abstract
(Sub-project to 839.08.250) Carrying capacity of an ecosystem is generally defined as the maximum or potential biomass in a system. In the Wadden Sea, only a small number of bivalve species represents the majority of the systems biomass. These dominant bivalves species form an important link in this ecosystem, as they filter the water column, act as bio-engineers, and serve as food for higher trophic levels. This group of filter feeders is represented by Blue mussels (Mytilus edulis), Cockles (Cerastoderma edule) and Soft-shelled clams (Mya arenaria) that are native to the Wadden Sea, and by the invasive Pacific oyster (Crassostrea gigas) and the Razorshell clam (Ensis directus). During the past few decades, the occurrence and distribution of these species seem to change. Mussel production decreases, while the biomass of the Pacific oyster and the Razorshell clam seems to increase. These developments are important for the modelling of the carrying capacity of the Wadden Sea ecosystem. Besides their ecological importance, these species are also of economic importance, especially in mussel aqua culture. This creates an area of tension in policy making. Also for policy making it is of importance to monitor the developments of these aggregated species in the Wadden Sea. This proposal aims to monitor the occurrence (biomass, size- and age distribution) of the dominant bivalve species and several biological and physical parameters that determine the dynamics of these populations. Because these species occur in aggregated subpopulations, and because the long-term survival of these species depends largely on the stability of the structure itself, the monitoring program adjusts to these characteristics. The proposed monitoring program consists of three work packages. Work package A comprehends the monitoring of the biomass and the size- and age distribution of the bivalve species. These data will be used for the improvement of the input in and the development of ecosystem models (proposal I1). Work packages B comprehends the monitoring of biological and physical parameters that are expected to affect the development and structure of the (sub)populations, and work package C comprehends the monitoring of the development and dynamics of subtidal and intertidal mussel beds and oyster reefs, making use of air-born photo analysis and Side Scan Sonar imaging.
Netherlands