Ulva intestinalis (Gut weed)


Type of fouling organism: Green algae

Algae include several groups of relatively simple, eukaryotic, living aquatic organisms that capture light energy with different pigments and use it through photosynthesis to convert inorganic substances into organic matter. Algae vary from small, single-celled species to complex multicellular species, such as seaweeds. Seaweeds live in the sea or in brackish water occupying both the inter and sub-tidal. The algae can be distinguished by the different pigments into three basic colours: red, green and brown. Green algae attribute their colour to the presence of the pigments chlorophyll a and b. Most species are aquatic and can be found in freshwater and marine environments. Some 8,000 species have been described with over 800 marine species. Green algae may be unicellular, multicellular, colonial or composed of one large nucleate/multinucleate cell.

Ulva intestinalis is a green seaweed found at all levels of the shore. It has inflated, irregularly constricted, tubular, generally unbranched fronds that grow out from a small base. The fronds may be 100 - 300 mm in length and have a diameter of 6 - 18 mm. The plant is a summer annual and decays to become a bleached and decaying mass towards the end of the summer season.

Environment and Habitat

- Photosynthetic nutrition occurring on all levels of the shore and is a common epiphyte on shells and other algae.
- High intolerance of substratum loss, smothering, abrasion.
- Intermediate intolerance of increases in suspended sediment and water flow.
- Low intolerance of increases in turbidity, wave exposure and desiccation.
- Tolerant of displacement, changes in salinity, decrease in wave exposure, water flow rate, and suspended sediment.


- Reproductive type: Alternation of generations.
- Reproductive frequency: Annual protracted.
- Development mechanism: Spores.
- Fecundity: > 1 million.
- Dispersal potential: > 10km.
- Duration before settlement: 8 days.


- Epiphyte.


- 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 occlude flow of water through nets.
- 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


- Considered to be worldwide in it's distribution.


Budd, G.C. & Pizzola, P., 2006. Ulva intestinalis. Gut weed. 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/Ulvaintestinalis.htm

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

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