Herbivorous fishes form a keystone component of reef ecosystems, yet the functional mechanisms underlying their feeding performance are poorly understood. In water, gravity is counter-balanced by buoyancy, hence fish are recoiled backwards after every bite they take from the substrate. To overcome this recoil and maintain contact with the algae covered substrate, fish need to generate thrust while feeding. However, the locomotory performance of reef herbivores in the context of feeding has hitherto been ignored. We used a 3D high-speed video system to track mouth and body kinematics during in-situ feeding strikes of fishes in the genus Zebrasoma, while synchronously recording the forces exerted on the substrate. These herbivores committed stereotypic and coordinated body and fin movements when feeding off the substrate and these movements determined algal biomass removed. Specifically, the speed of rapidly backing away from the substrate was associated with the magnitude of the pull force and the biomass of algae removed from the substrate per feeding bout. Our new framework for measuring biting performance in-situ demonstrates that coordinated movements of the body and fins play a crucial role in herbivore foraging performance and may explain major axes of body and fin shape diversification across reef herbivore guilds.

An underwater video system, positioned on the algal turf, was comprised of two high speed cameras and a synchronized force transducer. The system allowed the 3D tracking of the movements of the fish’s body, fins and mouth during feeding, while simultaneously measuring the forces they exerted on a feeding plate naturally colonized by turf algae. We focused on two species of Acanthuridae, Zebrasoma xanthurum and Zebrasoma desjardinii

Data_for_dryad – this dataset contains kinematic measurements of 40 feeding events from 16 different fishes of the species Zebrasoma xanthurum and Z. desjardinii, and the force they exerted during feeding. Measurements were calculated from 13 digitized points, along the fish’s body and the feeding plate, and were repeated for every phase of the feeding event: “mouth opening”, “mouth closing”, “head-flick” and “transport”. 

Removal_force_dryad – this dataset contains measurements of the force exerted and the amount of algae removed from 40 feeding plates which were fed upon by fishes of the species Zebrasoma xanthurum and Z. desjardinii