How do larvae attach to a solid in a laminar flow?

A hydrodynamic model explaining the mechanism of contact of marine larvae in vertical flows is presented. Two hydrodynamic factors-flow vorticity and larval self-propulsion-are the key components in the mathematical model. It is shown that flow vorticity causes a larva to rotate and change the direction of self-thrust, thus leading to its migration across the mean flow. The latter motion is of an oscillatory nature. Contact will be enabled only for sufficiently large amplitudes of oscillations. Simple expressions for the probability of initial contact are obtained for two-dimensional Couette and Poiseuille flows. The three-dimensional motion of a larva in a tube is studied using the Monte-Carlo simulations. It is shown that contact probability depends mainly on the ratio of the characteristic flow velocity and the larva's swimming speed. The theoretical results compare favorably with available experimental data. Possible applications of the method and results presented here to the classical problem of larval attachment to bodies of general geometry are briefly discussed in the concluding section.