Cirripedia is the subclass for Barnacles, a type of invertebrate arthropod. They are fascinating marine creatures that are typically found in shallow and tidal waters. Their hard, protective outer shells recognize them and are often seen clinging to a variety of surfaces, including rocks, ships, and even other marine animals.
As filter feeders, they consume tiny food particles from the water using their feather-like appendages. Despite their small size and stationary lives, barnacles possess a complex life cycle with a series of transitional stages, demonstrating the diverse ways life can adapt to survive in varying environments.
Appearance
Their bodies are enclosed in a series of calcareous plates that usually form a cone or cylindrical shape, providing them with a hard protective shell. This shell is often whitish or gray and can be quite rough to the touch.
Depending on the species, Barnacles range from 1-9 inches in length and 0.5-1.5 inches in height.
The only anatomical appendages on adult Barnacles, known as “cirri,” are their feet, which they utilize for respiration and grazing. These cirri are often feathery and can extend and retract to capture plankton from the passing water.
Mature Barnacles have hardly any inner organs. They lack gills and a heart.
Their hard outer plates have an opening at the top, which they close when there is a threat or when the tide has gone out, preventing them from drying out. Depending on the species, the arrangement and number of these plates can vary.
Although they appear to be immobile, barnacles start life as free-swimming larvae. After undergoing several molts, they find a suitable hard surface, attach their heads via a stalk or directly, and encase themselves in their distinctive hard shells.
The taxon is divided into three primary subdivisions: the Thoracica, comprising stalked and acorn barnacles; the Acrothoracica, which includes burrowing barnacles; and the Rhizocephala, made up of parasitic barnacles.
Habitat
Barnacles like places with lots of activity, like underwater volcanos and intertidal zones, where they reside on sturdy objects like rocks, pilings, and buoys. They also attach to moving objects like boats and ship hulls and whales.
After emerging from the egg, the larva swims freely for a brief while in search of a substrate to adhere to. It usually settles in locations where a large number of other barnacles exist, indicating that they are conducive to life. Before it can attach, the substrate it lands on must contain a layer of algal cells.
Barnacles produce a fast-curing adhesive that is one of the strongest known natural glues, with tensile strengths of 5,000 pounds per square inch and adhesive strengths of 22 to 60 pounds per square inch. It becomes sessile after it settles and may not move again for the rest of its life.
They are not picky about where they attach so long as the surface is hard and stable. They secrete a strong adhesive substance that allows them to firmly attach and stay put. Once they’ve chosen a spot, they remain there for the rest of their lives, which can be up to 20 years.
Diet
A Barnacle consumes either animal or plant matter, making its diet omnivorous. The majority are suspension feeders, they remain permanently inside their shells, which are typically made of 6 plates, and extend their modified legs into the water column.
Plankton and necrotic organic materials make up the food, which it eats by filtering and ingesting suspensions of these nutrients. It pushes the food inside using its cirri, which it stretches and retracts, then opens its opening to let water in before closing it again.
Reproduction
Despite being hermaphrodites, meaning they have both male and female sex organs. They cannot breed through self-fertilization and must cohabit with others to breed.
When one of them is ready to procreate, they extend an extraordinarily long penis over to a neighboring shell to deliver their sperm. The receiving barnacle holds the fertilized eggs until they develop into minuscule, alien-looking creatures with translucent bodies, feathery appendages, and two, short antennae. Then larvae are released into the ocean where they swim and grow.
As crustaceans, the nauplius larvae have hard shells and undergo a process known as molting, as they shed the old shell to grow a new one. After several molting cycles, the nauplius larvae grows into its next stage, a cyprid larvae,
They can have up to 6 hatchlings a year and lay hundreds of eggs once. The eggs molt into larvae throughout the winter inside the cavity. They scavenge for suitable sticking surfaces for a few weeks after the larval stage. Their life expectancy varies between 5-10 years.
Ecological Significance
Barnacles play a crucial role in marine ecosystems as filter feeders. They help maintain water quality by filtering out plankton and organic particles from the water, reducing excess nutrients that can lead to algae overgrowth.
By serving as a food source for predators like fish, sea stars, and birds, barnacles contribute to the marine food web. Additionally, their colonies create microhabitats on surfaces like rocks, shells, and ship hulls, providing shelter for smaller organisms and enhancing biodiversity in intertidal and subtidal zones.
Threats
A barnacle faces a variety of dangers, including rival barnacles seeking limited amounts of space. Mussels, starfish, limpets, whelks, and other types of sea snails are additional predators. They are the most susceptible to predators during the larval phase.
Barnacles are likely to be eaten by other aquarium inhabitants if they are maintained as pets. Worldwide consumption of some species is regarded as a delicacy. However, humans often scrape them off of ships and piers. The overall performance of ships in the water is negatively impacted by large populations, which raise their drag.
7 More Fantastic Facts About the Barnacle
- They are not parasitic. They do not harm or feed off the creature to which they attach.
- Their feet are used to feed.
- These sticky little crustaceans are linked to crabs and lobsters.
- Of the more than 1,400 species of barnacles, the most common ones are called acorn barnacles.
- They spend all of their life fixed to a single position.
- The oldest fossil crustaceans are in the Cambrian.
- They are economically significant as biofouling on ships, where they cause hydrodynamic drag, reducing efficiency.
FAQs
Are Barnacles harmful to humans?
They are permanently fixed to a surface for the rest of their lifespan; they possess no venom or teeth that would be harmful to humans. They can be consumed as well, making them completely harmless.
Do Barnacles fall off in freshwater?
When manatees join the relatively warm springs, they enter freshwater bodies in winter, where the Barnacles can’t survive in freshwater conditions, so they perish. They eventually come off, leaving a somewhat circular wound on the manatee’s back.
Do Barnacles hurt sharks?
Most Barnacles sift small food particles from the surrounding water as they rest on rough surfaces. Anelasma Squalicola, a particular species makes an exception. Sharks are consumed by a parasitic Barnacle that attaches to their flanks and scavenges nourishment off their tissue, eventually taking chunks.
Why do they remove Barnacles from boats?
Algae, slime, and other marine life can stick to a boat’s hull during the warmer seasons, impairing its efficiency. One of the strategies to maintain a boat smooth and clear of marine debris is to remove Barnacles and periodically scrub the bottom.
