Loggerhead sea turtles migrate thousands of miles through the world’s oceans, but they don’t travel solo — research shows they carry surprisingly meiofauna — tiny organisms smaller than one millimeter — on their backs. One loggerhead carried nearly 150,000 individual animals on its shell, including nematodes, crustacean larvae, and shrimp.
It was previously known that turtles carried some hitchhikers — but this quantity and degree of diversity hadn’t been seen before.
Studies of these tiny hitchhikers may help researchers trace the travels of these and other sea turtles, since certain meiofauna are unique to specific regions.
These microscopic animals include nematodes, which look like tiny worms and are found in just about every environment on Earth, from the deep sea to the soil of the highest mountains. They also found shrimp-like creatures called amphipods, tiny crustaceans called copepods, and jellyfish-like predators called hydroids.
Many larger hitchhikers such as shrimp and crabs often prey on smaller shell inhabitants.
Nematodes eat the bacteria and detritus that settles on the shell and, in some cases, they even eat other nematodes. Some of the larger animals such as barnacles can encrust and damage a turtle’s shell and increase drag, but they can also aid in camouflage. The tiny meiofauna, however, are unlikely to harm them.
The study raises questions about how these tiny animals get on the turtles in the first place — and how important turtles are for moving them about. It’s likely the turtles pick up many of the hitchhikers when they feed along the seafloor. Here, the reptiles do act as rafts, distributing hitchhikers over distances as they migrate. This may help explain how many tiny animals have become well-distributed, which remains something of a mystery, as many of these creatures cannot swim far or survive in the open ocean for long distances.