Membranipora membranacea (Sea mat)


Type of fouling organism: Encrusting Bryozoan

Bryozoa are sessile colonies of microscopic animals where each animal inhabits a separate box of the cuticle within the colony which is called a zooid. The zooid body has a fixed trunk and a lophophore for food collection. zooids are hermaphroditic. Gametes are passed out through the pores and fertilised eggs are internally incubated. After hatching motile larvae are released and while most are generally of short duration (minutes to hours), some can survive for up to a year in the plankton before settling. Bryozoa are common intertidal and subtidal animals, most are marine but there are some freshwater species.

Membranipora membranacea forms an encrusting lacy mat-like colony of very small, rectangular zooids, 0.42 x 0.13 mm in size. zooids are rectangular and fit neatly together in arranged rows that grow outwards and branch into new rows as the colony grows. The entire frontal surface is covered by a membrane and appears greyish white in colour.

Environment and Habitat

- Shallow marine habitats between the mid intertidal to the shallow sublittoral.
- Marine environments but can also live in brackish water.
- Encrusting colonies are typically found on the fronds of marine algae e.g. Laminaria digitata and Laminaria hyperborea.
- Occasionally small colonies can be found on Fucus serratus and in rock pools.
- Grows quickly (several mm / day) in response to predation from sea slugs.
- Rapid growth is seen in fast flowing environments.


- Reproduction type: Hermaphrodite.
- Reproduction frequency: Annual.
- Egg production: Springtime.
- Development: Planktonic.
- Settling time: 1 - 3 months (late summer-early autumn).


- Colonial.


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

Effects and Impacts

- Problematic for stock species.
- Reduces the value of shellfish and compete with them for space and resources.
- 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


- Found on algae on moderately exposed coasts throughout the north east Atlantic.


Rowley, S.J., 2004. Membranipora membranacea. Sea mat. 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/Membraniporamembranacea.htm

Tenkin M.H. Gamete Spawning and Fertilization in the Gymnolaemate Bryozoan Membranipora membranacea. The Biological Bulletin, Vol 187, Issue 2 143-155

Lazy Crust Bryozoan The Marine Fauna of Norway fauna/Mosdyr/membran.htm

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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