Response of offshore cultivated Laminaria saccharina to hydrodynamic forcing in the North Sea

The aim of the presented investigation was to test the sensibility of macroalgal aquaculture in offshore wind farms in the North Sea and to find arguments for the choice of appropriate sites among the planned wind farms. Based on experience with an offshore aquaculture farm of Laminaria saccharina conducted in 2002, we assessed the maximum hydrodynamic forces affecting farmed algae by applying the model software “WaveLoad”. Drag measured in a towing tank was considerably higher on algae with a more ruffled margin and wider blade collected from sheltered environments than on flat and narrow farmed Laminaria despite comparable blade areas. Drag varied according to frond size, current velocity and acceleration reaction. Dislodgement of laminarian holdfasts and the forces necessary to break the stipe depended on blade length and surface area. Neither did our measured nor our calculated values of drag exceed those forces, provided the algae had been grown in a current > 1 m s− 1. Even in storm conditions with maximum current velocities of 1.52 m s− 1 and wave heights of up to 6.4 m can cultivated L. saccharina withstand the high energy environment.