Edge vortex interaction minimizes drag in shrimp swimming

Shrimp propel themselves via metachronal paddling with five pairs of pleopods, generating both tip and edge vortices. In our high-fidelity 3D reconstruction and CFD simulations of the marsh-grass shrimp (Palaemonetes vulgaris), we found that interactions among adjacent pleopods significantly enhance propulsion and reduce energetic costs. Eliminating these inter-appendage interactions raised the cost of transport by 20%. During the recovery stroke, edge vortex merging reduces drag by 273% and power consumption by 137%, chiefly by aligning flow to lower pressure on the pleopods' anterior surfaces. These findings underscore the importance of edge vortices in improving swimming efficiency.