Survival chance of young mussel beds during fall

Abstract

To increase mussel areal in the Dutch Wadden Sea, restoration or creation of mussel beds is considered. Because Mussel beds often not survive their first winter, project Mosselwad studies stability and restoration opportunities. In order to determine the most effective way to restore an intertidal mussel bed an experiment was performed. Mussel plots were created from mussels transplanted from edges of the mussel bed to uncovered areas in front and in the middle of the bed, 5 at each location. For each location 4 control plots were created at the same height on a bare area south of the mussel bed. The hypothesis is that the plots represent young mussel patches in fall. Sheltered from waves they are expected to prosper in the middle of the mussel bed, but they erode in the other areas. The height variations of plots and their surroundings were monitored by a high resolution 3D laser scanner. Density changes were monitored by photographs, the bed stability by sediment samples and both the strength and direction of currents and waves by pressure sensors and velocity meters. Over successive monitoring days, the change in height was small and there was little variation in hydrodynamic conditions. Plots at the bare sand bank were however influenced by the direction of currents and waves. The height increase over plots in the mussel bed was constant and the decrease in mussel coverage minimal. Decrease in mussel coverage was the largest for plots at the bare sandbank. For these plots was the bed stability the smallest. Mussel patches inside the mussel bed, had a constant increase in height, a very small decrease in coverage and large bed stability and are considered to be most viable. Plots in front of the bed are however more viable than plots at the bare sandbank, which had a significant lower bed stability and a larger decrease in mussel coverage. Because mussel patches are more viable at a sheltered than at a new/bare location, it is recommended not to create new beds, but to restore the current mussel beds.