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.

Mytilus galloprovincialis is dark blue or brown to almost black in colour. The two shells are equal and nearly quadrangular. The outside is black-violet coloured; on one side the rim of the shell ends with a pointed and a slightly bent umbo while the other side is rounded. Shell shape can vary according to region between oval, subtriangular or pear-shaped. Average shell size typically only 50 - 80 mm.

Environment and Habitat

- Intertidal to subtidal.
- Rocky exposed coastlines with a high flow rate.
- Filter feeds on bacteria, detritus and phytoplankton.

Reproduction

- Reproduction Type: Separate sexes.
- Reproduction frequency: Annual.
- Fecundity: 1 million eggs per individual.
- Development of larvae: Planktonic.
- Larval settling time: 2 - 4 weeks.
- Life span: Dependent on habitat and location.

Communities

- Solitary and gregarious.
- Found in dense masses of up to 5 layers.
- Commonly fouled with barnacles and seaweed.

Equipment

- 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

Nets
- Onshore Net washing
- Coatings (Copper sulphate, fouling release coatings e.g. silicon)
- Mechanical cleaning of infrastructure (Disk cleaners)
- Air drying nets
Trays
- 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)
Shellfish
- 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

- Range extends north from the Mediterranean to the western French coast and south west shores of England, Wales and Ireland.

References

Global Invasive Species Database Mytilus galloprovincialis http://www.issg.org/database/species/ecology.asp?si=102&fr=1&sts

Janet Moore (2001) An Introduction to the Invertebrates. Cambridge University Press P2

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