The use of offshore energy conversion is predicted to expand significantly throughout estuarine and marine environments, with a global potential comparable to that of wind and hydro power. Therefore, it is important to study the interactions of offshore wave power devices with the marine environment. The Lysekil Project is a test park for wave power located about 100 km north of Gothenburg at the Swedish west coast. The concept is based on a linear wave power generator placed on the seabed, and connected via a wire to a buoy acting as point absorbers on the surface. Biofouling on offshore wave energy devices is an issue of concern for the operation or survival of the components. On the other side, these structures may provide habitats for marine organisms and thus increase biodiversity and form artificial reefs. In this chapter, size distribution and biomass of blue mussels on sheltered and exposed marking buoys are examined. Further, these results are used for calculating a worst case scenario of mussel growth on the lifting force of a specially designed toroidal buoy. The results show that more wave-exposed buoys were particularly favourable for blue mussel colonization, but that the hydrodynamic forces of the toroidal buoy were not significantly affected by mussel growth. Thus, biofouling is not necessarily negative for the wave energy absorbance of the wave power buoys.