Calanoid copepods, feeding currents, and the role of gravity.

Feeding currents of free-swimming calanoid copepods, observed through an expanded krypton laser beam and a back-focus dark-field optical system, show that these planktonic animals generate a double shear field to help in detecting food. The interrelation between flow field, perception of food items, and body orientation explains why these animals are generally negatively buoyant.