Barnacles are small crustaceans that attach themselves to hard surfaces like rocks, boats, and even sea turtles. If you’ve ever seen a sea turtle with white bumps on its shell, those are barnacles!

If you’re short on time, here’s a quick answer to your question: Turtles remove barnacles by shedding their scutes, rubbing against rocks, or seeking cleaning services from fish or sharks.

In this comprehensive article, we’ll explore how barnacles attach to turtles, the problems they cause, and the techniques turtles use to remove these pesky hitchhikers from their shells.

How Barnacles Attach to Turtles

Shell Anatomy

A turtle’s shell is made up of over 50 bones covered in keratinous scutes that form the smooth outer layer. The scutes are divided into marginal scutes around the edge, costal scutes on the ribs, vertebral scutes along the midline, and pleural scutes in between.

This bony armor provides protection but also offers anchoring points for barnacles to cement themselves.

Cementing to Scutes

Barnacles have a muscular stalk topped with an armored shell composed of calcareous plates. To attach to a turtle’s shell, barnacle larvae produce a strong cement glue that firmly bonds their base to the scutes.

This cement is incredibly tough and flexible, allowing the barnacles to adhere through the stresses of swimming, basking, and other turtle movements.

Some key facts about barnacle cement:

  • Adhesion strength can reach 9 megapascals, compared to standard superglues at around 2 MPa.
  • Cement cures rapidly, within 10-20 minutes.
  • Chemical composition involves proteins and polysaccharides.

Researchers are interested in studying barnacle cement for insights that could advance dental adhesives, bone implants, and other bioinspired applications.

Common Body Locations

Barnacles tend to accumulate on specific areas of a turtle’s anatomy:

Shell Region Reason for Settlement
Marginal scutes Access to water flow while turtle swims
Carapace (top shell) Elevated, flat surface exposed when basking
Plastron (belly) Smooth scutes, less algae growth

The exact distribution can help identify turtles’ habitat and behaviors. For instance, more plastron barnacles may indicate a turtle spends significant time inverted while resting underwater. While unsightly, most barnacles are relatively harmless symbionts just along for the ride!

Problems Barnacles Cause for Turtles

Increased Drag

Barnacles attaching to a turtle’s shell can significantly increase drag while the turtle is swimming, making it more difficult for the turtle to swim efficiently. Barnacles create roughness on the shell’s surface, disrupting water flow and creating turbulence.

This requires the turtle to exert more energy to swim at the same speed. Research has shown that green sea turtles with heavy barnacle growth on their shells experience 30% higher drag compared to barnacle-free turtles.[1] This extra effort to swim can negatively impact the turtle’s ability to migrate long distances, avoid predators, and forage for food.

Nutrient Deficiency

Large colonies of barnacles can become a significant drain on a turtle’s bodily resources. Barnacles are filter feeders, filtering enormous volumes of water daily to grab plankton and other food morsels.

This rapid filtering competes directly with the turtle’s own need to capture nutrients from the water. Heavy barnacle colonies may rob essential nutrients from the turtle that are critical for shell growth and maintenance, potentially leading to shell deformities or malnutrition.

One study found that loggerhead sea turtles with heavy barnacle loads had significantly lower levels of essential fatty acids compared to lightly fouled turtles.[2] Barnacles may also locally damage the shell surface they are attached to, creating pitting or erosion that further weakens the shell.

The nutrient drain and shell damage can become life-threatening if barnacle growth is left unchecked.

Shell Deformities

In severe cases, heavy barnacle fouling of a young turtle’s shell can directly cause deformities and abnormal shaping as the shell grows. One study on 106 green sea turtles found that individuals with excessive barnacle coverage often had highly irregular shell shapes, especially on the carapace (upper shell).[3] The barnacles outcompete the shell’s natural growth, resulting in asymmetrical domes and protrusions.

Shell deformities caused by barnacles make swimming less efficient and can hinder a turtle’s quality of life.

Additionally, the irregular shell shape provides more surface area for even more barnacles to attach, compounding the problem. Researchers thus recommend diligent removal of barnacles from juvenile turtle shells to prevent permanent damage during critical development periods.

For mature turtles, regular removal of barnacles is also crucial to limit drag and nutrient loss.


Shedding Scutes

Scute Growth Cycle

Turtles have a bony shell called a carapace that is covered with scutes. Scutes are made of keratin, the same material as human fingernails. As the turtle grows, its scutes also grow. The scutes are attached to the bony plates underneath but are not directly fused to them.

This allows the scutes to be shed and replaced over time. The shedding process is called molting.

Scutes grow in layers. New layers are generated underneath the visible older layers. The new layers push out the old scutes, which are shed from the shell in flakes or patches. Molting allows the shell to grow and expand as the turtle grows in size.

It also allows damaged scutes to be replaced with new healthy ones.

The molting process is gradual and continuous. Turtles may shed small flakes daily or patches of scutes periodically. Younger, growing turtles molt more frequently than adult turtles. The shedding happens naturally as part of the scute growth cycle.

It is not something the turtle purposefully does to remove barnacles or algae.

Shedding Process

The process of molting scutes generally follows this cycle:

  1. New keratin begins forming underneath the oldest visible scute layer.
  2. The new layers expand, loosening the old scute layer.
  3. The old scute layer peels away in flakes or patches, revealing the new layer underneath.
  4. The new scute layer then continues growing and generating additional layers beneath it.

Shedding usually begins at the center seam of the scutes and spreads outward. It can occur in small sections at a time or encompass a whole scute plate. The turtle may rub against surfaces to help loosen and remove the old layers.

Molting is a normal process and the turtle experiences no discomfort. The shedding can occur daily, weekly, monthly or seasonally depending on the turtle species, its age, health, and diet. Even after a scute is shed, some remnants may remain in crevices of the shell.

New Scute Formation

As new scute layers generate, they form according to the existing scute patterns. The new scutes will be similar in size, shape and placement to the old scutes. However, imperfections like scratches, pits, or abnormal shapes in the old scutes are replaced with smooth new growth.

In the case of injury where whole scutes are missing, the new layers can regenerate and fill in those areas. Over time, new scute growth can reshape injured or abnormal areas to match the normal scute pattern and appearance. This regeneration ability depends on the turtle’s health and age.

While scutes regenerate, the actual bony plates of the shell do not regenerate if damaged or deformed. The scute layers will mold to the existing shell structure as they regenerate. If the bony shell is malformed, the new scute growth will remain that way as well.

Rubbing Against Rocks

Turtles have developed an ingenious method for removing barnacles and other growths from their shells – rubbing up against rocks and coral. The rough, abrasive surfaces help scrape off pesky acorn barnacles, stalked barnacles, algae, and more from the keratin material that makes up the turtle’s shell (carapace and plastron).

This behavior allows turtles to groom themselves and keep their shells clean and functioning properly.

Abrasion Helps

Research has shown that over 90% of wild turtles exhibit shell-rubbing behavior as a form of self-grooming. The friction from abrasion assists with sloughing off dead tissue and flaking away unwanted debris and organisms sticking to the shell.

Some studios reveal that sea turtles may spend upwards of several hours rubbing themselves across underwater rocks to fully clear their shells. This demonstrates how essential shell-rubbing is for a turtle’s health and wellbeing.

Targeted Locations

Turtles appear to target particular locations on their anatomy to rub against surfaces. These areas on the carapace and plastron are harder to reach for the turtle and clear off itself. Some prime spots include the vertebral scutes along the dorsal shell midline and the coastal scutes along the lateral edges.

Interestingly, female sea turtles tend to exhibit more shell-rubbing due to egg laying activities that cause extra growth on the shell. By focusing abrasion on specific areas of shell fouling, turtles can efficiently remove barnacles and other organisms for cleaner shells and better performance in their aquatic environments.

Cleaning Stations

Mutualistic Relationships

Turtles have developed fascinating mutualistic relationships with certain fish species that help remove algae, barnacles, and parasites from their shells. At specialized sites called cleaning stations, turtles will wait in line for cleaner fish like wrasses, gobies, and butterflyfish to perform their services.

This interaction is beneficial for both parties. The turtles get cleaned of unwanted pests and organisms that slow them down or hurt them. Meanwhile, the fish get a free meal by picking off parasites and dead tissue—not just from turtles but also fish, eels, and even sharks and rays that visit the cleaning stations.

Common Cleaner Species

Some of the most common cleaner fish that form these relationships include:

  • Bluestreak cleaner wrasse – small bright blue fish that nibble parasites off larger hosts.
  • Cleaner shrimp – small shrimp species like the scarlet skunk cleaner shrimp that eat parasites and algae.
  • Hawaiian cleaner wrasse – picks parasites from turtles’ eyes, mouth, and cloaca.
  • Barberfish – a type of butterflyfish that nibbles old tissue off of sea turtles.

These species have sometimes coevolved with their hosts and developed tactics to signal their cleaning services, like distinctive dances, colors, or movements.

Effectiveness Varies

While cleaning fish can help slow the growth of barnacles and algae, their effectiveness has limits. Barnacles can grow back quickly, and a deep clean still requires manual removal by humans.

However, the interactions with cleaning fish likely provide some benefit. Research on green sea turtles in Hawaii showed that turtles visited cleaning stations more often when they had more parasites to remove.

So the fish help control parasite numbers, even if they can’t eliminate the problem entirely.


In summary, barnacles are a common nuisance for sea turtles, but fortunately these reptiles have evolved effective techniques to remove them. By shedding old scutes, rubbing against abrasive surfaces, and seeking cleaning services from fish, turtles can successfully rid themselves of barnacle infestations and maintain healthy shells.

Understanding how turtles eliminate these pesky epibionts gives us further insight into the amazing adaptions of these ancient mariners. With persistent self-cleaning behaviors, sea turtles persevere against the odds to live long lives roaming our oceans’ waves.

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