Movement data of barnacle Chelonibia testudinaria

<p>Movement is a fundamental characteristic of life, yet some taxa, such as barnacles, lose their capacity for locomotion as swimming larvae to become permanently affixed to a substratum as adults. Barnacles adopted this type of sessile life-stage at least 500 million years ago; however, we unequivocally confirm a prior report that the epizoic sea-turtle barnacle, <i>Chelonibia testudinaria</i>, has the capacity for self-directedlocomotion in the adult stage. We used time-series field and laboratory photographs to document its movement paired with transplant experiments employing various flow conditions and inter-individual configurations to test whether foraging or reproduction are ultimate causes of the activity. We also examined the barnacle cement microscopically for insight on its role in translocation. On loggerhead and green sea turtles, <i>C. testudinaria</i> moved distances up to 78.6 mm/year across its host substratum and in traverses on laboratory panels, occasionally altered course abruptly by 90^o. Our findings indicate these movements are behaviourally directed and not passively driven by external forces. Barnacles tended to move directly against water flow and independent of nearby conspecifics, suggesting that movement functions primarily to facilitate foraging, not reproduction. While the mechanism enabling this movement remains elusive, we observed that trails of cement bore signs of multi-layered, episodic secretion. We speculate that proximal causes of movement involve one or a combination of rapid shell growth, cement secretion coordinated with basal membrane lifting, and directed contraction of basal perimeter muscles.</p>