Project Objective and Approach
The objective of this case study (Wijsman et al. 2012) was to describe the effect of suspended sediment concentrations on the activity of filter-feeding bivalves (i.e. clearance rate, ingestion, pseudofaeces production and growth). The chosen model species was the blue mussel Mytilus edulis, since it is a ubiquitous and well-studied species with commercial importance and is regarded as an indicator species for filter-feeding bivalves.
An extensive literature search was made to identify potential effects of sand mining activities on the blue mussel. Two deterministic models are presented and their behaviour is compared with the data from the literature. This comparison was primarily made to get an impression of the order of magnitude of the rates and the nature of the relationships. The theory presents simple mechanistic rules that describe the uptake and use of energy and nutrients (substrates, food, light) and the consequences for physiological organisation throughout an organism’s life cycle.
These models, when properly tuned to the local situation, can be used to investigate or predict the impact of dredging on filter-feeding bivalve populations. The results can be used to decide how much increase in suspended solids is acceptable and what is the best period to carry out dredging and nourishment activities.
In order to calculate the effect of dredging activities on growth and development of a mussel, a Dynamic Energy Budget (DEB) model can be used to simulate the impact of increased suspended sediment concentrations on individual mussels (i.e. community effects are not taken into account). The DEB model includes a functional response that describes the energy uptake of a filter-feeding bivalve as a function of food and silt concentration. The patterns of the functional response are quite comparable with observations reported in the literature.
Prior and during marine construction activities like dredging, it has to be ensured that the activities are performed in an environmentally acceptable manner. For most dredging projects an Environmental Impact Assessment (EIA) is made, often specified and required by law or regulation. An EIA regularly contains an assessment of the potential effects of the project and can be taken into account in the project development and design stage. The DEB-model, as demonstrated in this case study, can be used to assess potential effects of dredging activities on bivalve populations.