THEORETICAL AND NUMERICAL STUDIES OF THE HYDRODYNAMICS AND CHEMORECEPTION OF CALANOID COPEPODS

Houshuo Jiang

Ph.D thesis, The John Hopkins University
September 2000, Baltimore MD

ABSTRACT: The hydrodynamics of a freely swimming copepod is studied theoretically and numerically. The results show that the geometry of the flow field around a freely swimming copepod varies significantly for different behaviors. A standing-still or slow-swimming copepod generates a cone-shaped and wide feeding current. Conversely, the flow field around a free-sinking or fast-swimming copepod is not like a feeding current, is not cone-shaped, but is narrow and long. These results are consistent with observations. The numerical results show that for the same amount of power expended, a standing-still or slow-swimming copepod is able to scan a larger volume of water than a fast-swimming one. The standing-still or slow-swimming copepod also generates a flow field that is more difficult to be detected by entrained prey. Thus, the standing-still or slow-swimming behavior benefits the copepod’s feeding. Based on the velocity data output from the numerical simulations, a three-dimensional alga tracking and chemical advection-diffusion model is used to calculate the deformation of the active space around an alga entrained within the flow field surrounding the copepod. The chemoreception capability of the copepod is evaluated for several different swimming behaviors. The results show that the standing-still, slow-swimming or free-sinking copepod can use chemoreception to detect remotely and locate individual algae entrained by the flow field surrounding itself. Conversely, the fast-swimming copepod may not be able to rely on chemoreception to detect and locate individual algae. For the standing-still or slow-swimming copepod, the advance warning time for an alga about to intersect the antennules of the copepod is found to be longer than that for an alga destined to go through the capture area of the copepod. This result supports the hypothesis that re-routing of algae in the feeding current is due to the advance warning from chemoreception. It is shown that in general the flow across the antennules does not pass through the capture area. Reorientation of the copepod in response to antennule inputs is necessary to capture the food particles passing outside the capture area and re-routing of the particles by the copepod increases the actual volume sensed and captured by the copepod.