Balanus crenatus (Acorn barnacle)


Type of fouling organism: Barnacle

Barnacles are a unique, and much modified group within the Phylum Crustacea. All barnacles are sessile marine animals, which remain fastened to hard substrates. When the barnacle is immersed under water, the upper shell plates open and the legs reach out casting a food collecting net. These basket like limbs are called cirri and filter food from the water and direct it towards the mouth. Barnacles have both male and female organs (hermaphroditic) and are all able to fertilise one another. As the adult stage is sessile, motile larval stages living in the plankton are the main method of dispersal. Barnacle larvae develop through a number of planktonic stages with the rate determined by feeding rate and temperature.

Balanus crenatus has a shell comprised of six shell plates, which forms a volcano-like cover. The shell plates are white and smooth and in large individuals the upper edges of the shell plates are usually slightly toothed or ridged. The shell is inclined to one end when viewed in profile. The base of the shell is calcareous with an average basal diameter of 25 mm.

Environment and Habitat

- Epifaunal, principally in the sublittoral but can be found in cryptic environments on the lower shore.
- Colonises most hard substrates available in the marine environment.
- Feeds on zooplankton, phytoplankton and detritus.
- High intolerance of substratum loss, smothering, desiccation, changes in temperature and oxygenation.
- Intermediate intolerance of abrasion, displacement and changes in nutrient levels.
- Low intolerance of fluctuations in salinity, turbidity, wave exposure and suspended sentence.


- Reproductive type: Hermaphrodite.
- Reproductive frequency: Annual.
- Age at maturity: 4 months.
- Development: Planktonic.
- Larval duration: 11 - 30 days.
- Dispersal potential: > 10 km.
- Life span: 1 - 2 years.


- Solitary.
- Permanently attached.


- Found on other biofouling organisms.
- Stock species particularly shellfish.
- Fishnets, cages, pontoons, shellfish trays, tanks, pipes and buoys.

Effects and Impacts

- Problematic for stock species as can compete for space and resources.
- Can obstruct the opening of bivalve shells.
- Can reduce the value of shellfish.
- Increases the weight of equipment.
- Increases labour and production costs as a result of cleaning and removal of biofouling.

Control/ Strategies and Management

- Onshore Net washing
- Coatings (Copper sulphate, fouling release coatings e.g. silicon)
- Mechanical cleaning of infrastructure (Disk cleaners)
- Air drying nets
- Manual cleaning (scrubbing and/or brushing)
- Low power washing
- High power washing
- Jet washing
- Air drying
- Lowering trays below photic zone during major spatfalls
- Biological Control (Sea urchins and periwinkles)
- Coatings (Copper sulphate, fouling release coatings e.g. silicon)
- Manual Cleaning
- Mechanical Cleaning
- Hot water 55oC for 5 seconds (Stock mortalities of ca 5% with this method)
- Dipping (Freshwater or chemical solution)
- Lowering lines below photic zone during major spatfalls
- Biological control (Sea urchins and periwinkles)
- Coatings (Copper sulphate, spiky coatings, fouling release coatings e.g. silicon)

Principles of Management

C Combat Settlement
P Protect Equipment and Stock
R Remove Biofouling


- Commonly found on western and southern coasts of the UK and Ireland, not so frequently on north eastern shores. Range runs from Norway in the north to the Atlantic coasts of France in the south.


White, N., 2004. Balanus crenatus. An acorn barnacle. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 05/02/2007]. Available from: species/Balanuscrenatus.htm

Janet Moore (2001) An Introduction to the Invertebrates. Cambridge University Press P1

Hayward P, Nelson-Smith T & Shields C (1996) Seashore of Britain and Northern Europe. HarperCollins Pubs.

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