Collective behavior and ambient flow in barnacle cypris larvae

Barnacles are small crustaceans, having two types of larval periods. While both of them swim, cypris larva is specialized in searching for and attaching to a surface without feeding. They tend to live in groups. It is known that the grouping can be induced by the settlement-inducing protein complex (SIPC). However, the grouping may be induced by various other factors such as phototaxis, water flow, substrate state, and communication between individuals. Few studies have focused on the detailed behavior of cypris larva, and none has on its collective nature. The phenomenon of collective behavior can be confirmed in various organisms. It is natural to expect some collective behavior of cyprids while swimming, since they live in groups, but no definitive evidence has been found. In this work, we visualized the flow around cypris larva during swimming, quantified the state of collective behavior, and calculated various statistics such as the correlation coefficient, in order to elucidate the communication between allogeneic individuals. We found the surrounding viscous flow and the small yet nontrivial correlation between them.