Boundary layer: a gradient in velocity that results from a fluid’s viscosity (“internal stickiness”) and the “no slip condition,” a phrase used to describe the tendency for a fluid to adhere to a solid surface. The thickness of the boundary layer provides an estimate of the distance any substance, such as an oxygen molecule, has to travel in order to move between the water column and a benthic organism. (return to essay)
Benthic: living attached to or very closely associated with the ocean bottom. (return to essay)
Feeding type: Benthic organisms all remove food from their immediate surroundings. Suspension feeders remove food directly from the water as it moves past their feeding surface. Deposit feeders sweep food from the surrounding sediments; often these organisms have long tentacles which do not work well in fast flows. Some organisms, such as brittle stars, are able to switch between deposit and suspension feeding modes as flow speeds change. (return to essay)
Multicellular organisms have bodies comprised of more than one cell. In contrast to unicellular organisms, multicellular organisms generally cannot have all of their cells in contact with the surrounding fluid; for each unit of volume, they therefore have to transport more materials per unit of surface area exposed to the surrounding fluid. (return to essay)
Shear: A term used to describe the rate of mixing, or “scrubbing” applied by a moving fluid to a surface. The higher the shear, the faster a clod card will dissolve. (return to essay)
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