Balanus improvisus (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 improvisus has a white or grey shell with a conical, smooth wall. The shell opening is diamond-shaped and toothed. The base is up to 15 mm in diameter, calcareous, flat, thin and permeated by pores with height being less than the base diameter.

Environment and Habitat

- Habitat - found from the mid shore to the sublittoral on rocks, algae and artificial surfaces in brackish water and estuarine areas.
- Often found in wave exposed areas.
- Feeds on zooplankton, phytoplankton and detritus.


- Reproductive type: Hermaphrodite.
- Reproductive frequency: Unknown.
- Age at maturity: 6 - 8 weeks.
- Development: Planktonic.
- Larval settling time: 2 - 5 weeks.


- 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 western Norway and the Baltic down to south Atlantic coasts of Spain and Portugal and into the Mediterranean and Black Sea.


Jonne Kotta Balanus improvisus Darwin (Balanidae, Cirripeda) Estonian Marine Institute, University of Tartu Tallinn, Estonia Sektorid/merebioloogia/MASE/Benthic_invertebrates.htm

The Biology of Barnacles

Balanus improvisus Exotics across the ocean
EU concerted action download/Balanus_p1.pdf

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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