How can kelp shape the coastline?

Kelp forests colonize a large portion of global coastlines and support diverse assemblages of organisms. To this end, their role in coastal ecosystems has been well studied.  However, the impact of kelp on the morphology of the coastlines upon which it colonizes is not as well known.  We quantify the effect of kelp on current driven coarse sediment transport by developing a model for the motion of coarse grains coupled to kelp fronds, and show that kelp significantly enhances particle mobility, allowing large grains to be transported at current velocities where their motion would typically be impossible.  Our model predictions agree well with a year of underwater observations of kelp-assisted sediment transport from the Strait of Juan de Fuca. 

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tl;dr Kelp can act like a sail on a sailboat. It effectively translates water forces to the attached particle, making the particle more mobile under low currents.