Effect of water motion on the cultivation of the commercial seaweed Undaria pinnatifida in a coastal bay of Galicia, Northwest Spain

Undaria pinnatifida is an edible brown seaweed, and its cultivation is being considered in Northwest Spain. Water motion is considered to be a key factor in growth and production of macroalgae; however, little is known about their influence on the farming of commercial seaweeds. In this study we investigated water motion effects on the cultivation of U. pinnatifida in a coastal bay of Galicia (Northwest Spain). Growth and morphological features of fronds and biomass yield were compared between two locations with different degrees of water motion (moderately exposed site vs. sheltered site). Growth rate, which was measured either as length and weight changes of fronds, was significantly higher for the moderately exposed site compared to the sheltered site. Fronds in the moderately exposed site were larger and had significantly more area and biomass of blades. The highest biomass yield was obtained at the moderately exposed site. Whether the environmental conditions at these locations were responsible for these results was explored. We suggest that the different hydrodynamic conditions may be the main environmental factor responsible for the results, as different hydrodynamics can affect the uptake of nutrients and carbon dioxide by reducing the diffusion boundary layer around the algal surface. According to this view, the degree of water motion at a culture site is a key factor that should be considered when identifying optimal locations for the cultivation of U. pinnatifida and other kelps in coastal bays.