As sessile animals, barnacles can quite easily, and rather unfairly, be dismissed as boring by virtue of their perceived ubiquitously immobile lifestyles. And while many barnacles do post up on unmoving structures such as rocks and pilings, many take to the road and adhere to ship hulls and mobile hosts like whales, sea snakes, crabs and sea turtles. Since these hitchhiking crustaceans may be a nuisance for a critter trying to move about, this epibiont-basibiont association falls somewhere on the scale between parasitism and mutualism.
Dr. John Zardus of The Citadel took particular interest on the relationship between 16 members of the barnacle superfamily Coronuloidea and all seven extant sea turtle species. By combing through publications, technical reports and data from museum collections, Dr. Zardus compiled a catalog enumerating barnacle-laden sea turtle species and the proportion hosting each species of barnacle, separated by geographic region (Atlantic Ocean, Caribbean Sea and Gulf of Mexico, Mediterranean Sea, Indian Ocean, Pacific Ocean and Central Indo-Pacific). These data spanned over the past 167 years, with over 30,500 turtles with barnacles documented! With this comprehensive information in hand, he asked: “Just how specific are the barnacle species to their sea turtle hosts, and will this vary geographically?”
Dr. Zardus found that in general, barnacles did not prefer only a single sea turtle species, but latched on to an average of three types of hosts. And just because a species of barnacle took a liking to one type of turtle in one region, didn’t mean they showed the same affinity in a different region! By far, the traveling crustacean that showed the least specificity was Chelonibia testudinaria, which latched on to every single turtle species. Green sea turtles (Chelonia mydas) took first place as a host; a whopping 13 of the 16 barnacle species were documented for them among all regions. By contrast, the small and region-specific Kemp’s ridleys (Lepidochelys kempii) cart around only three species. Barnacles Platylepas coriacea and Stomatolepas dermochelys showed the most specificity by only latching on to the leatherback sea turtles (Dermochelys coriacea), who are characterized by their soft carapace. On average, there were nine species of barnacle per region, with the greatest diversity in the Pacific Ocean (12 species) and the lowest occurrence in the Mediterranean Sea (six species).
These findings can be used to create species and region-specific “barnacle fingerprints” and inform future surveys focusing on where these sea turtles are traveling to and how they operate in their environment. These sessile crustaceans may not be so boring after all; but in fact, can be an ideal sentinel for aspects of sea turtle behavioral ecology.
“Barnacles, to the undiscerning eye, are as boring as rivets. This is largely attributable to the erroneous impression that they don’t go anywhere or do anything, ever.”
“Barnacle life is punctuated with adventurous travel, phantasmagorical transformations, valiant struggles, fateful decisions, and eating.”
- David Quammen, Point of Attachment, 1998
Dr. Danielle Ingle is a Postdoctoral Research Associate at Texas A&M University at Galveston, where she is currently investigating the form and function of sea turtle rhamphothecae (keratinous beaks) from species local to the upper Texas coast. You can reach her at firstname.lastname@example.org