Anomia ephippium (Saddle oyster)


Type of fouling organism: Bivalve

Bivalves are molluscs and include species of oyster, scallop, mussel, cockle and clam. All are aquatic and most are marine. Their body is laterally compressed between two halves of a hinged shell. Many bivalves are sedentary with a foot that secretes a number of byssus threads that enables them to attach to the substratum. Feeding is by way of two main ciliary tracts located on enlarged gill surfaces within the mantle which is contained in the shell. Hair-like structures (cilia) produce water currents and trap food particles beating them towards labial palps allowing small particles to be conveyed to the mouth

The shell of Anomia ephippium is thin and brittle and circular in shape, with a white or grey colour. Individuals can grow up to 60 mm in size. The right valve is smaller than the left and is usually flat with a hole for the byssus to attach to hard substrates. The left valve is convex and uppermost when viewing the attached organism.

Environment and Habitat

- Habitat - lower intertidal to subtidal (down to 150 m) attaching to hard substrates, including other mollusc shells and algal holdfasts.
- Filter feeding organism.


- Reproductive type: Separate sexes.
- Reproductive frequency: Unknown.
- Development of larvae: Planktonic.
- Larval settling time: Unknown.
- Dispersal potential: > 10 km.
- Age at maturity: Unknown.
- Life span: Unknown.


- Solitary.


- Mussel rope culture, oyster and suspended pectinid culture.
- Fishnets, cages, pontoons, shellfish trays, tanks, and 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


- Distribution ranges from Iceland to West Africa and also found in the Mediterranean.


Neal, K.J., 2004. Anomia ephippium. Saddle oyster. 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/Anomiaephippium.htm

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

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

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