Plankton active response to turbulence enables efficient transport

Although plankton typically have slow swim speeds relative to ocean flows, they can potentially enhance their transport by exploiting certain flow features. For example, a theorized 'surfing' strategy describes how plankton can preferentially sample upwelling areas of the flow by simply sensing and actively reorienting in response to local velocity gradients. In this study, we present the first experimental evidence that real plankton may be able to surf turbulence. We studied the bottom-heavy, planktonic larval snail Crepidula fornicata as our model organism. By observing these plankton in a jet-stirred turbulence tank, we show that they indeed have complex responses to velocity gradients. In particular, we found that they actively rotate to oppose the local vorticity, which contrasts with the typical passive, gyrotactic response. We compared our observations with those of simulated surfing plankton to demonstrate the applicability of the surfing theory to our data, where we found good agreement. Finally, we observed that the real plankton can preferentially sample upwelling areas of the flow in some cases, enhancing their transport relative to their swimming speed alone, similar to the proposed surfing theory.