Plankton Safari

Viscous Flow

Many calanoid copepods create a feeding current in order to increase the encounter rate with suspended food. The question then is: how do the animals pluck the food items from the feeding current?

The animal, Eucalanus pileatus, was tethered to a dog hair. Algae were in the water at natural densities. A micropipette filled with india ink delivered the tracer of the flow (india ink). The flow is generated by the movements of the mouth parts. The inner mouth parts remain motionless until an alga is close-by and detected. Then a fast movement is executed to capture the alga. Thus, the flow is disturbed for a short moment. The question then is: how did the animal “know” that an alga was close-by?

This clip is from a high-speed 16 mm movie made in 1979 by Tim Cowles, Mimi Koehl, Gus Paffenhofer, and Rudi Strickler in Strickler’s laboratory.The clip was transferred to digital video and condensed into a FLASH file. The clip is 29 seconds long at 30 frames per second, but was originally made at 250 frames per second. Therefore, the real scene is only 3 1/2 seconds in duration.

For more, see: Koehl, M.A.R. and J.R. Strickler. 1981. Copepod feeding currents: Food capture at low Reynolds number. Limnol. Oceanogr. 26, 1062-1073