Crabs wandering along the seafloor or scuttling through tide pools often appear encrusted with bumpy white or pink growths. Upon closer inspection, these lumpy protrusions are actually barnacles that have attached themselves to the crab’s shell. This phenomenon leads to the question – what exactly are these bizarre barnacle growths on crabs?
An Overview of Barnacles
Barnacles are a type of small crustacean that anchors itself to hard surfaces like rocks, ship hulls, dock pilings, and even the shells of other marine animals. After cementing themselves in place, barnacles filter feed by extending feathery appendages to catch plankton floating by.
Of the over 1,400 identified barnacle species, the most common are called acorn barnacles. These have conical volcano-shaped shells made up of calcareous plates that surround the animal inside. Acorn barnacles thrive in highly active environments like wave-swept rocky shores and harbor pilings.
Why Barnacles Grow on Crabs
Crabs make the perfect moving surfaces for barnacle colonization and growth. A crab’s hard outer shell provides an ideal anchoring point for the barnacles’ powerful adhesive. As the crab moves about the seafloor and intertidal areas, juvenile barnacles floating around as larvae attach and transform into adults.
Once one barnacle establishes itself on a crab, it releases pheromones that attract other barnacles to join the party. In this way, whole clusters of barnacles accumulate on the shells of crabs over time. This is especially evident on older, larger crabs. Massive colonies of literally thousands of barnacles may crust the entire shell and even the eyestalks of ancient crabs.
For the barnacle, hitching a ride on a mobile crab provides better access to food and oxygen. As the crab moves and forages the barnacles get exposure to fresher currents full of plankton to filter feed on. They also get transported to new areas to expand their range.
Impacts on the Crab Host
This relationship is one-sided – the barnacles benefit while the crab suffers A heavy accumulation of barnacles makes it harder for a crab to walk, swim, eat, and escape predators. The extra weight and drag of a barnacle-encrusted shell stresses the crab’s metabolism and makes it expend more energy going about its daily business.
Barnacles may also obstruct the crab’s vision or block its mouthparts, further impacting its ability to find food and avoid danger In extreme cases, thousands of barnacles can virtually immobilize a crab
Barnacles attach using an extremely powerful cement-like adhesive. Prying off established barnacles can rip chunks out of the crab’s shell, making it vulnerable to infections. So crabs have a high incentive to prevent barnacles from attaching in the first place.
Crab Defenses Against Barnacles
Crabs have evolved various tactics to discourage or dislodge barnacle settlers before they grow. These include:
- Grooming – Using mouthparts and claws to scrape off barnacle larvae and recently attached juveniles
- Molting – Shedding the outer shell which removes established barnacles in the process
- Masking – Coating the shell with mud or algae to prevent barnacle adhesion
- Crushing – Forcing the underside of the shell against surfaces to crush settled barnacles
Smaller crabs and young instars are better at grooming, molting frequently, and hiding under rocks or crevices to avoid barnacle infestation. Older, larger crabs tend to accumulate the most extensive barnacle colonies since they molt less often. Their sheer size also makes self-grooming barnacles away much harder.
A Closer Look at Crab and Barnacle Interactions
- Hermit crabs don’t have their own shell, so they can’t molt away barnacles. Instead, they must pick abandoned shells already colonized by barnacles.
- Pea crabs and skeleton shrimp cohabitate inside shells with hermit crabs. They eat juvenile barnacles living in the shell walls.
- Mud and masking crab species actively coat their shells in sediment that makes attachment difficult for barnacles.
- King crabs on Alaska’s seafloor face predation from giant ribbon worms. But their barnacle armor makes them distasteful to the worms.
- Barnacle shells have growth rings similar to tree rings. Researchers can count the rings to determine a barnacle’s age.
- After settling on a crab, barnacles spend their whole lives attached right to that spot. They can’t relocate if conditions worsen.
A Symbiotic Twist – the Sacculina Barnacle Parasite
A bizarre type of barnacle called Sacculina actually infects crabs from within. Sacculina barnacle larvae land on a crab and send rootlets throughout the crab’s body. It draws sustenance directly from the crab blood and fat reserves.
As the parasite spreads inside the crab, it castrates the crab and causes degeneration of muscles and organs. The crab stops molting and essentially becomes a zombie host at the mercy of the parasitic Sacculina.
The infected crab’s behavior completely changes as the barnacle manipulates it to optimize conditions for its own growth and reproduction. The crab stops showing normal evasive behaviors, making it more vulnerable to predation. This benefits the Sacculina since being eaten allows transmission to a new host.
So in the case of Sacculina barnacles, the symbiotic relationship becomes less mutualistic and more exploitative to the crab’s detriment. This provides a fascinating example of how intricate ecological relationships can exist between marine organisms like crabs and barnacles.
In conclusion, the persistence of barnacles living on crabs illustrates a complex struggle for resources between two organisms sharing the same habitat. While unsightly and detrimental for the crab, the shells of accumulated acorn barnacles also showcase how intertwined different sea creatures’ lives are.
The sight of a barnacle-crusted old crab reminds us these armored animals have survived many years and challenges in their coastal environment. For a crab, barnacle infestation is just another hardship to endure in order to continue foraging, migrating and reproducing in the vulnerable intertidal zone they call home.
Weak 170 170 31 26 116 92
- Attack – Deal standard physical damage to single target.
- Icicle – Deal damage to single target.
- Poison Strike – Deal physical damage to single target. Inflict Poison(The target will take elemental damage at the end of their turn) for 3 turns.
Encounters[]
| Japanese | Romanized |
|---|---|
| アオコケバサミ | Aokokebasami |
Parasitic Barnacle Facts: the BARNACLE You’ve NEVER HEARD OF
FAQ
Are barnacles on crabs bad?
Yes, barnacles can be harmful to crabs. While some barnacles are harmless and can even be beneficial in some cases, others, particularly rhizocephalan barnacles, can cause significant harm to crabs.
Why do fishermen remove barnacles from crabs?
The process involved carefully removing the barnacles to ensure the crab’s health while also taking note of some rotten spots that needed attention.
What is a crab barnacle?
Sacculina is a species of barnacle that infects crabs and then manipulates their behavior to benefit itself—all to the detriment of the unsuspecting crab. They do so by growing a rootlike system throughout the crab’s entire body, which the parasite uses to feed on the crab.
Can I eat crab legs that have barnacles on them?
Yes, you can eat crab that has barnacles on its shell. Barnacles are typically harmless and do not affect the quality of the crab meat. However, it’s important to clean the crab thoroughly before cooking and consuming it. The barnacles themselves are usually not eaten, as they are tough and not particularly palatable.