Sea turtles often carry an array of marine life on their shells, with barnacles being among the most commonly observed. The presence of barnacles on a turtle’s shell is a common sight in marine environments, representing a unique biological interaction.
Barnacles: The Hitchhikers of the Sea
Barnacles are crustaceans, related to crabs and lobsters, that spend their adult lives fixed in one place. Their life cycle begins with a free-swimming larval stage, crucial for dispersal and finding a suitable attachment site. The initial larval form is the nauplius, which then develops into the cyprid larva.
The cyprid larva is the stage specifically adapted for searching and attaching to a surface. These larvae possess specialized sensory organs that help them detect chemical cues and surface textures, indicating a suitable substrate. Once a desirable location is found, the cyprid larva uses a strong, permanent adhesive cement secreted from its antennules to firmly secure itself. This attachment is irreversible, and the larva then undergoes metamorphosis into its sessile adult form, characterized by its hard, calcareous plates.
Turtles: Ideal Mobile Habitats
Sea turtles offer a particularly suitable and stable substrate for barnacle attachment. Their hard, durable carapaces, or upper shells, provide a relatively non-shedding surface. Unlike many other marine animals that periodically shed their skin or exoskeletons, a turtle’s shell grows continuously, offering a consistent attachment point for the barnacles.
The relatively slow movement of many sea turtle species also contributes to their suitability as hosts. This reduced speed allows barnacle larvae sufficient time to settle and attach without being dislodged by rapid motion. Furthermore, sea turtles have exceptionally long lifespans, which provides a long-term, stable habitat for barnacle colonies to develop and thrive. Their continuous presence in marine environments, where barnacle larvae are abundant, increases the probability of successful colonization.
A One-Sided Arrangement: What Barnacles Gain
The relationship between barnacles and sea turtles is largely commensal, meaning the barnacle benefits while the turtle is generally unaffected. An advantage for barnacles is enhanced dispersal and transportation. By attaching to a mobile host like a sea turtle, barnacles are carried to new feeding grounds and areas where they can find mates. This “hitchhiking” strategy allows them to access resources and reproductive opportunities they would not have if fixed to a stationary rock.
Another significant gain for the barnacles is a constant supply of food particles. As the turtle moves through the water, it creates a continuous flow, bringing plankton and other suspended organic matter directly to the barnacles, which filter feed. This ensures a steady food source without the barnacle expending energy to create its own current. Additionally, being on a large, mobile host like a sea turtle can offer protection from some predators that might target barnacles fixed to stationary objects.
Impact on the Turtle Host
However, under certain circumstances, barnacles can cause minor issues for the sea turtle host. These problems typically arise with heavy infestations or specific deep-burrowing barnacle types.
Large numbers of barnacles can create increased hydrodynamic drag on the turtle’s shell, potentially leading to a slight reduction in swimming efficiency. This additional drag might require the turtle to expend more energy for movement. Rarely, certain deep-burrowing barnacle species can cause minor irritation or superficial erosion of the shell, especially if they attach near or on soft tissues. Excessive burrowing could lead to localized discomfort or, rarely, provide a pathway for secondary infections. Professional intervention to remove barnacles is considered for severe infestations affecting the turtle’s health or mobility.