VISUALIZATION OF SEAWATER FLOW AROUND MORPHOLOGICALLY DISTINCT FORMS OF THE GIANT-KELP MACROCYSTIS-INTEGRIFOLIA FROM WAVE-SHELTERED AND EXPOSED SITES

Our objective was to determine whether blades of Macrocystis integrifo lia from a wave-sheltered site possess morphological features that ''t rip'' velocity boundary layers (VBL) from laminar to turbulent in cond itions of low water motion compared to blades from a wave-exposed site . The movement of seawater around morphologically distinct blades of M . integrifolia from wave-sheltered and exposed sites was visualized in a recirculating flow tank in which seawater Bow was initially laminar at velocities up to 8 cm s(-1). Turbulent VBLs were observed for both blade morphologies at free-stream seawater velocities of 2 cm s(-1), and at a Reynolds numbers of between 10(2) and 10(4), which is lower t han that predicted from boundary layer theory. Flow around blades from a wave-sheltered site was dominated by separation induced by large ed ge undulations. For the wave-exposed morphology, the flow pattern was similar to that along a smooth, flat plate, but the observed thickness of the VBL was up to a factor of 2, greater than that predicted from laminar or turbulent boundary layer theory. There were no obvious diff erences in how structural features such as marginal spines and bulbs a ffected seawater flow around the different blade morphologies.