Abstract
Movement is a fundamental characteristic of life, yet some invertebrate taxa, such as barnacles, permanently affix to a substratum as adults. Adult barnacles became ‘sessile’ over 500 Ma; however, we confirm that the epizoic sea turtle barnacle, Chelonibia testudinaria, has evolved the capacity for self-directed locomotion as adults. We also assess how these movements are affected by water currents and the distance between conspecifics. Finally, we microscopically examine the barnacle cement. Chelonibia testudinaria moved distances up to 78.6 mm yr−1 on loggerhead and green sea turtle hosts. Movements on live hosts and on acrylic panels occasionally involved abrupt course alterations of up to 90°. Our findings showed that barnacles tended to move directly against water flow and independent of nearby conspecifics. This suggests that these movements are not passively driven by external forces and instead are behaviourally directed. In addition, it indicates that these movements function primarily to facilitate feeding, not reproduction. While the mechanism enabling movement remained 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.
Highlights
The goal of movement ecology is to determine how, why, where and when organisms move [2,3,4]
The substratum inhabited may bear on the phenomenon, but while some epibiotic barnacles associate with particular sea turtle species [20], C. testudinaria is the least host-specific of the turtle barnacles [21] and is found on manatees [22] and crabs [23]
The specimens were fed live adult Artemia once per day, the seawater was changed daily and the shell surfaces were brushed clean every 3 days to avoid algal overgrowth. This experiment was repeated but in the second instance, we used three C. testudinaria obtained from the carapaces of dead stranded green sea turtles
Summary
The goal of movement ecology is to determine how, why, where and when organisms move [2,3,4]. The specimens were fed live adult Artemia once per day, the seawater was changed daily and the shell surfaces were brushed clean every 3 days to avoid algal overgrowth This experiment was repeated but in the second instance, we used three C. testudinaria obtained from the carapaces of dead stranded green sea turtles. These barnacles were once again photographed in apical, lateral and basal view but photos were taken daily instead of weekly. We placed five barnacles on to 16 × 16 cm acrylic plates at an inter-individual distance of 5 cm (electronic supplementary material, figure S1E). Several C. testudinaria had mature ovaries and testes upon dissection at the end of the experiment, suggesting that many individuals were reproductively active during the experiments
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