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|78.4 - Summer 2005|
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By Brandon Schneider
Although sea turtles themselves have been extensively studied, research has focused very little on the diverse organisms that inhabit turtles’ shells and skins. These small creatures, which include barnacles, crustaceans, and even sucker fish, are known as epibionts.
“Work gets done on sea turtles; what doesn't get looked at, indeed what gets bypassed quite a bit, is their epibionts,” remarks Theodora Pinou, assistant professor of biological and environmental sciences at Western Connecticut State University. Pinou, a herpetologist, has teamed with Eric Lazo-Wasem, an invertebrate specialist, to study epibionts. Both researchers are affiliated with the Yale Peabody Museum. The research on epibionts in Mexico is part of a larger Sea Turtle Conservation Project that Pinou and Lazo-Wasem are working on conjunction with Alejandro Peña of the University of Guadalajara in an effort to save and hatch more endangered sea turtles. Undergraduates Lindsay Demaree and Emily Schenker are also assisting the team.
Eric Lazo-Wasem, an invertebrate specialist affiliated with the Yale Peabody Museum, studies epibionts. (Credit: Eric Lazo-Wasem)
Theodora Pinou, assistant professor of biological and environmental sciences at Western Connecticut State University, is a collaborating herpetologist for this project. (Credit: Theodora Pinou)
One of the initial steps in the program is to classify the collected epibionts. The Conservation Program studies Olive Ridley turtles (Lepidochelys olivacea) as they come ashore to nest at Costa Carayas, or the Turtle Coast, on the Mexican Pacific coast. Since most previous studies have focused on Atlantic or Mediterranean turtles, little is known about Olive Ridley turtles or their epibionts. In fact, only one paper has been written on epibionts of Pacific marine turtles.
Some of Pinou and Lazo-Wasem’s findings have been quite surprising. “There’s a small crustacean we’ve found that has only been reported maybe three times in the literature in the past, say, one hundred years,” states Lazo-Wasem. “It isn’t rare, but it’s rarely collected.”
Other organisms leave Lazo-Wasem questioning whether a new species has been discovered. To find out, there is no choice but to head to the library for some old-fashioned taxonomy. Lazo-Wasem consulted an article from 1879 to determine whether this epibiont is the same as ones associated with whales and a related species or is of a different species altogether.
“There’s nothing wildly new about epibionts,” Lazo-Wasem concedes. “Barnacles were described by Darwin and even earlier, but now, in the context of other questions that we’re starting to ask about them, [this field] is starting to develop.”Sinister Symbiosis
One such question being studied is the effects of epibionts on the health of the turtle. Most epibionts are harmless as they reside on the turtle’s shell and live off algae. Barnacles attach to any hard surface, including ships, piers, and the hard shell of a turtle. Using their wispy legs, barnacles grab at planktonic organisms from water flowing by. Though these organisms do not feed parasitically off the turtle’s resources, however, their effects may not be completely neutral, especially when they reside in the skin of the turtle.
Stomatolepus praegustator is such a barnacle often found in the skin of the neck and flippers. “It is sort of like a wart on the turtle’s skin,” explains Lazo-Wasem, “but, actually, the skin [has] to grow around it, and the barnacle grows in concert. It does cause some physical damage to the skin, but the overall impact of these things is really not known.”
Another specimen found in lesions of sick, captive-bred turtles had first been reported in Japan. Though they were found in abundance on the turtles, it was not known whether they direcly caused the sickness nor whether the crustaceans, in smaller numbers, would significantly affect the turtle’s health. Current sampling methods, in which epibionts are scraped from female turtles as they create nests, collect specimen only from turtles healthy enough to swim ashore and lay eggs. However, there may be turtles in the ocean severely impaired by excessive epibionts in the skin that can no longer nest and thus are not studied.
A second class of epibionts, named “ectoparasites,” are commonly thought to harm their host organism. Leeches are part of this category, yet even their effect on sea turtle health remains unknown.
“Your first impression is that [the leech] can’t be doing any good,” says Pinou, “and I would agree. But I have no evidence to show that it’s a problem. When I looked at the literature, it said that leeches are attaching to the turtle but eating the algae.” This would render the relationship an example of mutualism.Epibionts and Evolution
After collecting enough data, Pinou and Lazo-Wasem will begin exploring coevolutionary trends between the sea turtles and their epibionts using genetic analysis. The researchers are interested in whether the mutualistic relationship between sea turtles and epibionts has led them to follow linked evolutionary paths.
“We want to look at how the sea turtles are related and how the epibionts are related, and then we want to ask if they have shared an evolutionary history,” Pinou explains. The research team will create and compare phylogenetic trees to determine genetic similarity. For example, they would first create a phylogenetic tree of a single species of epibionts found on three different turtles and then chart the relationship of the three turtles in another tree for comparing the degree of similarity between the turtles.
Does an entire family of epibionts live on one particular sea turtle or are the samples stochastically placed on the tree? Pinou admits, “I honestly don’t know what to expect, but either way I will learn something.”
Some epibionts—barnacles, for example—have an aquatic larval stage. After a few days, the larvae attach to a nearby surface, such as a sea turtle swimming by, to use as a substrate for their feeding. Epibiont placement on sea turtles may be entirely random, but there are so many unresearched variables that a working hypothesis is nearly impossible to create. How far do epibiont larvae swim? How far do the host turtles swim?
“It’s really humbling,” comments Pinou. “There is so much to solve, so much to learn. We’re just beginning to see that there’s such a world out there that we have no idea about.”About the Author
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