Studying ctenophore maneuverability with reduced-order analytical modeling

Ctenophores are centimeter-scale zooplankton capable of performing complex maneuvers by metachronally coordinating eight rows of cilia-based paddles (ctenes) that circumscribe their bodies. We used high-speed videography to study the maneuverability of Bolinopsis vitrea. From the animal experiments, we have observed three potentially different turning mechanisms: sharp, wide, and reversal turn. During sharp turns, only the ctene rows on the outside of the turn are active. For wide turns, all ctene rows are active; however, the beat frequency varies between opposing pairs of ctene rows. During reversals, ctenophores perform sharp turns while transitioning from backward to forward swimming, which also slightly changes the body orientation. Despite these observations, we do not have a systematic understanding of how rowing coordination impacts maneuverability. To explore the role of ctene row coordination, we developed an analytical model of a ctenophore swimming freely in three dimensions. This model allows us to calculate the forces created by the ctenes under these three different turning scenarios. The results from both experimental observation and analytical modeling show that ctenophore propulsion is a prime candidate to inform future bioinspired aquatic vehicles.