Sea turtles navigating the ocean often carry an assortment of organisms on their shells. Among the most noticeable are barnacles, crustacean relatives of crabs and lobsters. These shelled creatures find a home on the turtle’s hard carapace, a natural phenomenon observed across various sea turtle species.
Why Barnacles Choose Turtles
Barnacles seek out sea turtles as hosts due to several ecological advantages. A primary benefit is the stable, mobile surface a turtle’s shell provides, offering a solid attachment point for sessile organisms. Being on a moving turtle gives barnacles constant access to new water, bringing in plankton and other food particles they filter for sustenance. This passive feeding mechanism is more efficient than if they were stationary.
Turtles also act as a dispersal mechanism, allowing larvae to spread to new areas and colonize different oceanic regions. Attaching to a large, active animal like a sea turtle can offer protection from benthic predators. The turtle’s movement and size deter threats, providing a safe environment.
How Barnacles Attach
The process of barnacle attachment begins in their larval stages. Barnacles start as free-swimming nauplius larvae, which feed and molt through several stages. These larvae transform into the cyprid larva, adapted for finding a suitable surface for permanent attachment. The cyprid explores potential surfaces, including a turtle’s shell, using specialized antennules.
Once a suitable spot is identified, the cyprid attaches head-first. It secretes a powerful, fast-acting, proteinaceous adhesive, often referred to as biological cement, from specialized glands. This glue allows for permanent fixation. After this irreversible attachment, the cyprid transforms into the sessile adult barnacle, encased in its calcareous shell.
Effects on Sea Turtles
For the most part, the relationship between barnacles and sea turtles is commensal, meaning the barnacles benefit without significantly harming or benefiting the turtle. Barnacles do not feed on the turtle itself; they filter feed from the water. However, the presence of barnacles can sometimes lead to negative impacts on the turtle, particularly with heavy infestations.
Large numbers of barnacles can increase hydrodynamic drag and the overall weight of the turtle, making swimming more difficult and requiring more energy expenditure. This increased burden can reduce swimming efficiency and make foraging harder. If barnacles attach in sensitive areas such as near the eyes or mouth, they can interfere with the turtle’s vision or ability to feed properly. In some cases, certain barnacle species, especially those that burrow slightly into the shell or skin, can cause irritation, lesions, or even create small entry points for pathogens, though this is less common with typical sea turtle barnacles. A high barnacle load can also indicate a turtle is in poor health, as healthy turtles are more active and may naturally shed some barnacles.
Natural Detachment and Human Intervention
Sea turtles have several natural mechanisms to shed barnacles. As they grow, sea turtles periodically shed their scutes, the keratin plates covering their shells, which can naturally dislodge attached barnacles. This molting process is a continuous part of their growth. Turtles may also rub against rocks, coral, or other submerged objects to dislodge barnacles and other epibionts from their shells. This self-grooming behavior helps to keep their shells clean.
Human intervention to remove barnacles from sea turtles is generally limited to specific circumstances. Wildlife professionals, often in rescue or rehabilitation settings, will remove barnacles if the infestation is severe and demonstrably impacting the turtle’s health, mobility, or ability to forage. Improper removal by untrained individuals can cause significant harm to the turtle’s shell or skin, potentially leading to infection or further injury. In the wild, most barnacle presence is considered a natural part of the sea turtle’s ecosystem.