The truth about turtles

Image: Working with turtle ecologists, the FSU team ensured the least amount of interference with this vulnerable marine species. Photo by Matthew Ware, Florida State University. All photographs of loggerhead sea turtles were taken during research activities permitted by the Florida Fish and Wildlife Conservation Commission (permit #MTP-18-239) under conditions not detrimental to these animals. These images were taken under red light and converted to blackand-white in post-processing. Please do not attempt to recreate such images without a permit. 

"The place where the story happened was a world on the back of four elephants perched on the shell of a giant turtle. That’s the advantage of space. It’s big enough to hold practically anything, and so, eventually, it does.” Terry Pratchett, The Last Hero

Reading the recent news article, ‘Researchers uncover a world of life on the back of a turtle’, published on our website on 4 June, it was impossible to resist contacting the researchers to ask what it was like investigating life on the back of giant turtles on behalf of all Terry Pratchett fans out there. As it turns out, however, the most exciting results from this research focus on a much smaller ecological phylum.

This international team, led by Florida State University (FSU) researchers, opted to sample meiofauna, which are organisms roughly between 1 and about 0.032mm in size. Specifically, they focused on a type of aquatic meiofauna called nematodes, also known as roundworms.

“Nematodes are the most abundant animal on the planet,” said Ingels. “It has been said that four out of five animals on the planet are nematodes. They live everywhere.”

People have investigated animals and plants living on the backs of turtles for some time, but no one had investigated microscopic organisms. So, when Ingels arrived at the Florida State University Coastal and Marine Lab and noticed a turtle ecology survey underway on a nearby island with a naturally high density of nesting loggerhead turtles, he took the opportunity to include the collection and examination of meiofauna in the already active survey. Working with turtle ecologists, they were able to ensure the least amount of interference with this vulnerable marine species

Image: The FSU researchers worked with a team from Brazil, led by Professor Giovani dos Santos and Professor Yirina Valdes

 ‘I don’t think the Turtle gives a bugger… to tell you the truth.” Terry Pratchett, Small Gods

"What I am interested in are the microscopic creatures living on the turtle’s back,” explains Ingels. “I don't really care that much whether it is a turtle or not… but a turtle shell is a very intriguing substrate for the organisms I am interested in. You can compare the complexity of a turtle shell with other hard substrates, such as rocks, sea defences or sea plants.”

"To find nematodes on loggerhead turtle carapaces is no surprise, but when we compared their numbers and diversity to those from other hard surfaces or even on marine plant life, we realised their carapaces abound with this microscopic life," Ingels said.

‘Gods come and go, and still the turtle moves.’ Terry Pratchett, Small Gods

Ingels also noted that turtles are mobile; they swim large distances. So, whatever they are carrying on their backs has to come from somewhere and, indeed, is going somewhere.

“One of the main research questions was to ask if there is a link between where the turtle has been, where we find it, and if we can assess that link using these meiofauna?" he said.

The FSU team, in collaboration with a team from Brazil, sampled the shells from 24 loggerhead turtles that migrated to Florida's St. George Island in the summer of 2018 to lay eggs. Sample collection happens only after each turtle has laid her eggs and covered her nest. Once the turtle biologists have carried out their survey work, the meiofauna biologists begin theirs.

"Our sampling effort to get everything off that carapace is very intense because there is only thing on the mind of a turtle after it has finished nesting and that is to get back to the sea. I didn't realise that it is basically impossible to stop a turtle physically! It just rolls you over… it is just a very hard-shelled bulldozer that can just push you over.”

The team did, however, find some ways to make their lives a little easier.

“If you gently tap a turtle’s shell it'll move away from the direction of the tap which sometimes helps slow it down. Meiofauncologists are interested in all the things you can’t see, so we basically sponge down the entire shell and then carefully store everything we remove in special jars."

The researchers examined a forward, middle and posterior section of each shell to see if the different areas had different microscopic communities. They found thousands of meiofauna organisms. One turtle had more than 146,000 individual organisms living on its carapace - more than double the number of organisms than previously observed. By including the nematodes found in this new study, the researchers added at least 111 new species to the list of organisms that can live on the backs of loggerheads. A count that doesn't include other types of meiofauna, meaning that the final number could be even greater.

The team also found that the posterior section of the shells, closest to the rear flippers, had different communities and a higher diversity of species and that individual turtles harbour significantly different communities of meiofauna on their shells.

"Our results suggest loggerhead turtles are hotspots for organism abundance and biodiversity," said Ingels. "We suspect that larger organisms that are able to form structures serve as habitats for microscopic creatures and allow for greater levels of abundance and biodiversity."

"There was the theory that A’Tuin had come from nowhere and would continue at a uniform crawl, or steady gait, into nowhere, for all time.” Terry Pratchett, The Colour of magic

The research may help explain a paradox around the microscopic species: How can the same types of aquatic meiofauna be found in different parts of the world, hundreds or even thousands of miles away?

Researchers think they are able to travel large distances on the backs of sea turtles, which could help explain their widespread distribution.

“Our study demonstrates that if we go beyond what is visible and study the microscopic organisms on sea turtles, we can reveal rich and abundant life where it has not been recognised before. Were these turtles colonised by microorganisms in different places?" asked Ingels. "It's exciting because it means we may be able to infer where loggerheads have been based on the microscopic communities on their shells."

Images: Left - Pselionema, Right - Richtersia

Tens of thousands of microscopic organisms can colonise loggerhead turtles, which visit remote coasts and beaches during their migration. It makes sense that there would be a connection between the locations frequented by the turtles and the places where the same meiofauna are found. A better understanding of that link could help inform conservation practices for these reptiles.

The study, ‘Meiofauna Life on Loggerhead Sea Turtles-Diversely Structured Abundance and Biodiversity Hotspots That Challenge the Meiofauna Paradox’ was published in the journal Diversity.

"Information on key areas used by loggerhead turtles is crucial to inform their management, as it helps identify key threats that this vulnerable species are exposed to," said Mariana Fuentes, a co-author of the article and assistant professor of oceanography in the FSU Department of Earth, Ocean and Atmospheric Science.

Authors:

Jeroen is assistant research faculty with the Florida State University Coastal and Marine Laboratory and Mariana is an assistant professor of oceanography in the Department of Earth, Ocean and Atmospheric Science at Florida State University.