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Role of self-propulsion of marine larvae on their probability of contact with a protruding collector located in a sea current

Settlement of marine larvae on a substrate is a fundamental problem of marine life. The probability of settlement is one of the quantitative characteristic of the settlement process. The probability of larval contact with a substrate is the upper bound of the probability of settlement. This work addresses the problem of contact probability and contact rate of marine invertebrate larvae with an isolated protruding collector located in an unbounded sea current. There are two common approaches to the problem of contact probability. In one, a collector induces certain cues, which help a larvae find the collector. In such a case, the larva moves towards the collector deliberately, using its navigation and propulsion devices. In the second approach, a larva moves towards a collector as a passive small particle. In this case, the cause of contact of a larva with a collector is a mechanical collision of a small moving body with a large obstacle. We considered a larva which does not know the location of the collector, which does not use its navigation device yet uses its self-propulsion. We mimicked a larva by a tiny self-propelled underwater vehicle, moving in shear flow of a large obstacle. We illustrated our approach by studying contact of a larva of the Bryozoan Bugula neritina with a cylindrical collector. We observed the behavior of this larva in a laboratory flume, and according to the observations formulated a mathematical model of larval motion in shear flow. The trajectories of a large number of larvae, starting their motion far from a collector with random initial conditions are calculated numerically, and the probability of their contact with a collector is estimated. The results of Monte-Carlo simulations illustrate that larval self-propulsion may increase the probability of their contact with a collector by orders of magnitude compared to passive particles.