Helical swimming by jet-propelled salp colonies in the ocean

Helical swimming is common among microorganisms and has inspired the development of swimming microrobots owing to their high performance at low Re.  However, there are few reported cases of larger swimmers that rely on a helical swimming pattern. Salps are cm- to meters-long colonial organisms that coordinate multiple jet-propelled swimming units to achieve efficient swimming.  The salp species, Weelia cylindrica, swims in a helical pattern but it is unknown what drives this swimming pattern and whether helical swimming confers any propulsive advantages over non-helical swimming salp species.  We recorded the three-dimensional swimming paths of W. cylindrica via a SCUBA diver-operated stereo camera system to address the following questions: 1) are helical swimming trajectories driven by morphology, kinematics or, both? and, 2) do helically swimming salps achieve higher swimming speeds than their non-helical-swimming counterparts?  The details of W. cylindrica swimming mechanics offer insights into performance of helical swimming driven by the coordination of multiple jets.