Skip to main content
U.S. flag

An official website of the United States government

Kelp, cobbles, and currents: Biologic reduction of coarse grain entrainment stress

January 1, 2016

Models quantifying the onset of sediment motion do not typically account for the effect of biotic processes because they are difficult to isolate and quantify in relation to physical processes. Here we investigate an example of the interaction of kelp (Order Laminariales) and coarse sediment transport in the coastal zone, where it is possible to directly quantify and test its effect. Kelp is ubiquitous along rocky coastlines and the impact on ecosystems has been well studied. We develop a physical model to explore the reduction in critical shear stress of large cobbles colonized by Nereocystis luetkeana, or bull kelp. Observations of coarse sediment motion at a site in the Strait of Juan de Fuca (northwest United States–Canada boundary channel) confirm the model prediction and show that kelp reduces the critical stress required for transport of a given grain size by as much as 92%, enabling annual coarse sediment transport rates comparable to those of fluvial systems. We demonstrate that biology is fundamental to the physical processes that shape the coastal zone in this setting.

Citation Information

Publication Year 2015
Title Kelp, cobbles, and currents: Biologic reduction of coarse grain entrainment stress
DOI 10.1130/G36616.1
Authors Claire C Masteller, Noah J Finnegan, Jonathan Warrick, Ian M. Miller
Publication Type Article
Publication Subtype Journal Article
Series Title Geology
Series Number
Index ID 70169218
Record Source USGS Publications Warehouse
USGS Organization Pacific Coastal and Marine Science Center