Balanus trigonus (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 trigonus is a small, steep-sided, conical barnacle, with six shell plates. The colour of its base is pink, with characteristic, white coloured vertical ribs with purple lines in between. The mouth of the shell is triangular, and the small plates that close the shell opening bear distinctive rows of small pits. Average size is a height of 15 mm and a diameter of 20 mm.

Environment and Habitat

- Subtidal to depths of 150 m.
- Found in both turbid and clear waters.
- Found sheltered from waves and in bays, rarely seen in estuaries.


- Reproductive type: Hermaphrodite.
- Reproductive frequency: All year round.
- Age at maturity: 3 weeks.
- Development: Planktonic.
- Larval duration: Unknown.


- Solitary.
- Permanently attached.


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

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


- Range includes eastern Atlantic and Mediterranean.


Gulf States Marine Fisheries Commission Balanus trigonus nis_factsheet.php?toc_id=121

Australian biological resources study Species Bank Balanus trigonus Australian Government Department of the Environment and Water Resources cgi-bin/species-bank/

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

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

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