Data for "Short wave attenuation by a kelp forest canopy"

Giant kelp (Macrocystis pyrifera) forests are common along the California coast. Attached on the rocky bottom at depths of approximately 5 to 25m, the kelp, when mature, spans the water column and develops dense, buoyant canopies that interact with waves and currents. Based on observations of surface gravity waves carried in a Point Loma, California, kelp forest, and we present two novel results. First, we report short wave (1-3s) attenuation in kelp, quantified by an exponential decay coefficient a~O(10^{-3}m^{-1}) - comparable to the dampening effect of sea ice. Second, we identify seasonal and tidal changes in attenuation, peaking mid-summer with maximum kelp cover, and during low tide when a greater proportion of the fronds are at the surface. Thus, the surface canopy of a kelp forest can act as a naturally occurring, temporally varying high-frequency filter for wave energy.