Large number of microscopic organisms found living on the shells of turtles

New research has revealed that the shells of loggerhead turtles can support entire communities of microscopic life with a much greater abundance and diversity than previously realised, raising important questions about marine meiofauna and loggerhead conservation.

algae on back
Turtles shells have been known to be covered in algae and barnacles, but it is the amount of microscopic life invisible to the naked eye which is really impressive

Throughout the animal kingdom large animals have always played host to microscopic life, whether they are aware of it or not. Even humans can carry an abundance of species with them as they go, including viruses, bacteria and even bigger hitchhikers like lice and tics. In the underwater world this is no different, especially for animals like turtles, whales and crustaceans with large solid surfaces that are ideal for microscopic communities to grow on. However a new study led by researchers at Florida State University has revealed that loggerhead turtles can take this to the next level by supporting entire worlds of microscopic life that are far more abundant and diverse than previously suspected. It suggests that these oceanic reptiles may be far more ecologically important than previously believed, as well as providing researchers with the means and motive to help protect them.

Sampling shells

This new study into the shells of loggerhead turtles, recently published in the journal Diversity, was carried out by researchers from Florida State University with help from another team of scientists from Brazil. They were looking at the abundance of meiofauna, organisms roughly between 1mm and about 0.032mm in size, on the shells of turtles nesting on Florida’s St. George’s Island in the summer of 2018. In total they sampled the shells of 24 loggerheads, by carefully scraping and sponging the very top layer from their carapace after they had laid their eggs. After collecting their samples from across the shells they then released the turtles, who remained unharmed by the process, to return to the water. The samples were later analysed by the team from FSU in the lab.

scraping shells
Researchers scrape of the samples from the carapace of a loggerhead turtle on St. Geroge’s Island

Surprising results

To the researcher’s surprise they found that the samples taken from the loggerhead turtles contained an abundance and diversity of meiofauna far greater than previous research had suggested there would be. In particular microscopic nematodes, also known as roundworms, that had been previously dismissed as a potential inhabitant of turtle carapaces. In fact 111 species of nematodes were found living on the shells, which more than doubles the previous 100 species of meiofauna thought to be able to live there, not including the other species from different taxonomic groups the researchers discovered as well. In terms of abundance, one turtle was found to have 146,000 individual organisms living on its back! Lead author Jeroen Ingels, speaking to Science Daily, explained that the turtle’s shells were “abound with this microscopic life, the extent to which had hardly been documented in the past”.

nematodes
Nematodes (as seen under a microscope) were abundant in the shell samples

Carrying communities

If this wasn’t enough, the researchers also found that each loggerhead turtle supported its own unique community of meiofauna with certain species found on some turtles and not on others. This led them to ask a new question “were these turtles colonized by microorganisms in different places?” and if so, could they be responsible for the success of meiofauna in our oceans? It has always remained something of a paradox in marine biology that most microscopic creatures in our oceans have a much greater geographic range than other species, despite not being able to travel large distances themselves. This new finding suggests loggerheads and other turtles, may have played a significant part in this by proving a sort of ‘turtle highway’ for these creatures to spread around our oceans.

migration map
An example of satellite tracking data from sea turtles shows how far they can travel across ocean basins and why they could help spread microscopic communities across our oceans

Ecologically important

Not only is this an extremely interesting discovery, but it also highlights just how ecologically important loggerhead turtles really are, with an entire world of microscopic life literally living on their backs. This makes their conservation even more important, because without them microscopic communities throughout our oceans could be significantly impacted. Luckily this same discovery also provides a way of helping protect these ocean wanderers too. “It means we may be able to infer where loggerheads have been based on the microscopic communities on their shell” explains Ingels, who calls this an ‘exciting’ development in turtle conservation. He thinks that by analysing the microscopic communities on shells could allow his team to tell where they have been over the last few months, much like an electric satellite tag could. More research is needed to test the validity of these claims, but if it works it could seriously help with conservation efforts to save them.

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