Installing offshore structures, such as wind farms and floating solar panels, introduces large amounts of artificial hard substrate into previously soft sediment-dominated areas. These substrates are rapidly colonized by filter-feeding organisms, such as mussels, which have high filtration capacities and extract significant quantities of phytoplankton and suspended particulate matter (SPM). The mussels then egest undigested material as biodeposits (fecal pellets or pseudofeces). In recent decades, the Belgian part of the North Sea has experienced significant changes in SPM dynamics that are poorly understood. Our study hypothesizes that biodeposits from blue mussels (Mytilus edulis) contribute to reduced turbidity by promoting particle aggregation and altering floc structure, density, and settling velocity. To test this, we conducted a laboratory experiment to assess the impact of biodeposits on SPM flocculation. Using a custom-made flocculation chamber, we monitored turbidity and particle size distribution in two treatments: (1) kaolinite and seawater, and (2) biodeposits, kaolinite, and seawater. Initially, both treatments were subjected to a high turbulent shear rate (75 s⁻¹) to homogenize the mixture, followed by a lower shear rate (20 s⁻¹) for 120 minutes to promote aggregation. The results indicate that flocs formed from kaolinite combined with biodeposits were larger than those formed by kaolinite alone and that the median floc size increased more rapidly in the presence of biodeposits. However, turbidity decreased at a similar rate for both treatments during the flocculation experiments. Overall, our study demonstrates that biodeposits released by mussels have the potential to significantly enhance sediment aggregation, thereby influencing the dynamics of SPM in areas adjacent to offshore structures. |
