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.
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.
Video of kelp-assisted sediment transport, Strait of Juan de Fuca, Washington, USA (I.M. Miller)
 Presenting at the UCSC Graduate Research Symposium. This presentation won the Alumni Award for Best Presentation. |
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 Kelp RockImage from underwater tripod at the mouth of the Elwha River in Washington state. |
 Kelp RockImage from underwater tripod at the mouth of the Elwha River in Washington state. |
 Kelp-Grain Force BalanceSchematic illustration of kelp-assisted entrainment model |
 Model Results & ObservationsModel output for both the grain-only force balance and the grain and kelp force balance models for incipient motion with consideration of a range of kelp frond lengths. Dots indicate underwater observations. |
 Coarse-grained beachesLarge cobbles populating beaches near the mouth of the Elwha River. Some cobbles still have kelp fronds attached. |
Masteller, C.C., Finnegan, N.J., Warrick, J., Miller, I., (2015), Kelp, Cobbles, and Currents: Biologic reduction of coarse grain entrainment. Geology. [link]