Purple Barnacle
Purple Barnacle or Megabalanus tintinnabulum is a species from the family Balanidae. The latin name meaning handbell refers to the miniature bells or barrel-shaped like barnacles. It is distinguished from other members of the genus by having growth ridges on the external plates by having no spines or spiny projections. The Purple Barnacle can be either rough or smooth, and they are sometimes slightly folded. The basal margin of the shell is either straight or slightly sinuous. The colour is a pale shade of reddish or bluish purple, sometimes streaked longitudinally with a darker or lighter shade and sometimes with transverse bands of colour. Each Purple Barnacle is a unique shape and form and there are no two alike.
The Purple Barnacle commonly refers to certain barnacle species that have a purplish coloration, often due to pigmentation or encrusting algae growing on their shells. However, there isn't a widely recognized species officially called "Purple Barnacle." You might be referring to one of the following:
Possible Interpretations of "Purple Barnacle"
1. Amphibalanus amphitrite (sometimes appears purplish)
A common barnacle species found in warm and temperate waters worldwide.
Often has a slightly purplish or dark tint due to shell coloration or encrusting organisms.
2. Chthamalus species
Some species may have purplish hues due to shell colour or attached algae.
3. Encrusting barnacles with purple algae
Sometimes barnacles appear purple because of encrusting coralline algae or other marine algae growing on them.
General Info About Barnacles
Class: Cirripedia (crustaceans)
Habitat: Attached permanently to hard surfaces like rocks, ships, piers, shells
Feeding: Filter feeders, use feathery appendages (cirri) to capture plankton
Ecological Role of Barnacles
1. Filter Feeding & Water Quality
Barnacles are suspension feeders: they extend feathery appendages (cirri) to filter plankton and organic particles from seawater.
By filtering large volumes of water, barnacles help improve water clarity and contribute to nutrient cycling.
2. Habitat Formation & Biodiversity Support
Barnacles form dense colonies on rocks, ship hulls, shells, and other hard surfaces.
Their shells create microhabitats and refuge for many small marine organisms such as algae, small crustaceans, worms, and juvenile fish.
Barnacle beds increase local biodiversity by providing structure in otherwise bare environments.
3. Food Source
Barnacles are an important food source for many predators:
Sea stars, whelks, fish, birds, and some crabs feed on barnacles.
They form a critical part of the coastal food web.
4. Biofouling Agents
Barnacles are notorious for biofouling — attaching to ship hulls, piers, buoys, and other man-made structures.
While this can cause economic costs, it also creates new habitats for other fouling organisms, contributing to artificial reef ecosystems.
5. Indicators of Environmental Change
Because barnacles are sessile and sensitive to environmental conditions (temperature, salinity, pollution), they can be used as bioindicators to monitor coastal ecosystem health.
Barnacle Adaptations for Filter Feeding
1. Feathery Appendages Called Cirri
Barnacles possess modified thoracic legs called cirri.
These are long, feathery, and fringed with fine hairs (setae).
The cirri extend out of the shell to sweep plankton and detritus from the water.
They rhythmically wave the cirri back and forth, creating water currents and capturing suspended food particles.
2. Sessile Lifestyle with Hard Protective Shell
Barnacles are permanently attached to a hard substrate and enclosed in a tough calcareous shell.
This stable position allows them to remain in areas with good water flow, optimizing food delivery.
The shell protects them from predators and environmental stress.
3. Operculum (Opening Doors)
The barnacle’s shell has an operculum—a set of plates that open to allow the cirri to extend out and close tightly to protect the animal when feeding is not possible or danger is near.
This allows barnacles to feed when conditions are favourable and seal up when they need protection.
4. Ability to Detect Water Flow
Barnacles can sense changes in water flow and often adjust their cirri beating accordingly.
They can increase feeding activity when plankton-rich water flows by.
5. Efficient Particle Capture
The fine hairs on the cirri trap very small plankton and organic particles.
As cirri retract, captured food is moved toward the mouth.
6. Slow Metabolism and Energy Use
Barnacles have a slow metabolism, allowing them to survive periods with less food.
They can close their operculum and wait out unfavourable conditions (e.g., low tide exposure).
Why These Adaptations Matter
They enable barnacles to exploit plankton in moving water efficiently.
Adaptations protect barnacles in harsh intertidal zones with strong waves and predators.
Their filter feeding helps maintain ecosystem nutrient balance.
Barnacle Life Cycle
1. Adult Stage (Sessile)
Adult barnacles are hermaphroditic—each individual has both male and female reproductive organs.
They are permanently attached to a substrate inside a hard shell.
Despite being sessile, they reproduce sexually by exchanging sperm with nearby neighbours.
2. Mating
Barnacles have an exceptionally long, extensible penis relative to their body size, which they use to reach neighbouring individuals (sometimes up to 8 times their body length).
Fertilization is internal, with sperm transferred directly to the neighbour's mantle cavity.
This is crucial since they can’t move to find mates.
3. Egg Development
Fertilized eggs develop inside the parent barnacle’s shell, often brooded within the mantle cavity.
The larvae hatch as free-swimming nauplius larvae.
4. Larval Stages
Nauplius larva: A tiny, planktonic stage with several molts. It swims freely and feeds on plankton.
After several molts (usually 5–6), the nauplius transforms into the cyprid larva.
5. Cyprid Larva (Settlement Stage)
The cyprid larva does not feed but searches for a suitable hard surface to settle.
It uses specialized antennal attachment organs to explore and choose the ideal substrate.
Once settled, it secretes a glue-like substance to permanently attach itself.
6. Metamorphosis
The cyprid undergoes metamorphosis into a juvenile barnacle.
It develops its calcareous plates and starts building its protective shell.
Eventually, it grows into a mature sessile adult, completing the cycle.
Reproductive Strategies
Hermaphroditism: Each barnacle can produce eggs and sperm, increasing reproductive opportunities.
Spermcasting: They transfer sperm directly via their long penis to neighbours—sometimes multiple partners.
Brooding: Eggs are retained and protected inside the adult until larvae hatch.
High larval dispersal: The planktonic larvae can disperse widely before settling, increasing genetic mixing and colonization.
How Barnacle Larvae Select Settlement Sites
1. Surface Exploration
The cyprid larva uses its specialized antennules (small sensory organs) to “walk” or crawl lightly over potential surfaces.
These antennules have adhesive pads and sensory receptors that detect chemical and physical cues.
2. Chemical Cues
Barnacle cyprids respond strongly to biofilms—thin layers of bacteria and microalgae that coat submerged surfaces.
Chemicals released by:
Conspecific adults (other barnacles already settled),
Microbial biofilms, and
Certain algae or invertebrates
can attract or deter larvae.
This helps cyprids find habitats where barnacles thrive or avoid poor-quality or hostile environments.
3. Physical Surface Characteristics
Larvae assess:
Surface texture (roughness or smoothness),
Hardness (solid rock vs. soft sediment),
Orientation (vertical vs. horizontal surfaces),
Light exposure (preference often for shaded areas to reduce desiccation risk).
Rough, hard surfaces are generally preferred for better attachment and protection.
4. Presence of Conspecifics
Barnacles tend to settle near existing barnacle colonies to form dense aggregations or “beds.”
This clustering provides protection from predators and increases reproductive success since neighbours are close enough for sperm transfer.
5. Environmental Conditions
Factors like water flow, salinity, temperature, and predation risk influence settlement.
Some species prefer turbulent, oxygen-rich water; others favour calmer or more sheltered spots.
6. Permanent Attachment
Once satisfied, the cyprid secretes a strong, quick-setting adhesive from glands in its antennules.
It cements itself permanently to the chosen spot and undergoes metamorphosis into a juvenile barnacle.
