Modelling of diffusion boundary-layers in subtidal macroalgal canopies: The response to waves and currents

A model is described for nutrient uptake by the giant kelp Macrocystis integrifolia Bory that incorporates blade boundary-layer dynamics. The model input is derived from field measurements of water motion near wave-exposed and wave-sheltered M. integrifolia beds. Factors considered in the model include (i) the distinction between uni-directional and oscillatory flow in wave-exposed and -sheltered locations, (ii) the reduction in boundary-layer thickness due to wave-driven flow and (iii) the tight packing of M. integrifolia beds at low tide which can reduce the in-canopy flow rates. The velocities are incorporated into the model which indicates that uptake rates can vary between 5 to 300% of the steady-state equilibrium value depending on the flow regime. [PUBLICATION ABSTRACT]