The kelp Laminaria hyperborea is a dominant component of the subtidal nearshore ecosystem and is
subjected to a heterogeneous wave and current climate.Water motion is known to influence physiological
processes in macroalgae such as photosynthesis and nutrient uptake attributed to mass-transfer limitation.
The study attempts to establish the effect of water motion on the growth rates of blades and elongation
rates of the stipes of L. hyperborea at adjacent wave-exposed and wave-sheltered locations over a
12 month period from field observations. The observations were supported by detailed physical and chemicalmeasurements
(light, temperature, seawater nutrient concentrations and hydrodynamics) and of tissue
carbon and nitrogen concentrations together with δ13 carbon. Despite a 30% difference in the root mean
square of the velocity (Velrms) between the two survey locations, there was no evidence to suggest that
water motion had any direct influence on the growth rates of either the blades or elongation of stipes of
L. hyperborea. No significant differences were observed between either environmental or plant physiological
variables between the sheltered and exposed locations. Using an integral velocity parameter (Velrms) the
present study also highlighted the importance of the tidally induced current component ofwater flowin the
subtidal zone.