Type of fouling organism: Brown 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. There are about 2,200 species of brown algae and most are marine. Typically, brown algae are larger and more species are found in colder waters. The kelps are the largest and the most complex in this group and are the only brown algae with internal tissue differentiation. The giant brown kelp is harvested for use in commercial products such as toothpastes, soap, ice cream, and a range of other applications.

Alaria esculenta is a kelp with a claw shaped holdfast with a short cylindrical stipe with wavy membranous lamina ca 70 mm in length on either side. The frond can deteriorate over time and only the midrib remains. Their colour is yellow to olive green with a supple and flexible to texture. A. esculenta grows to a maximum length of 2 metres.

Environment and Habitat

- Found from low intertidal to subtidal, generally to 8 m depth but on very exposed shores be found at depths of up to 35 m.

Reproduction

- Reproductive type: Alternation of generations.
- Reproductive frequency: Annual episodic.
- Age at maturity: 8 - 14 months.
- Development: Spores.
- Larval duration: 1 day.
- Dispersal potential: 10 - 100 m.

Communities

- Permanently attached.
- Solitary.
- Found in high densities.

Equipment

- Stock species particularly shellfish.
- Fishnets, cages, pontoons, shellfish trays, tanks, pipes, pumps and filters.

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

- Found on North Sea and north Atlantic coasts.

References

Tyler-Walters, H., 2006. Alaria esculenta. Dabberlocks. 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: http://www.marlin.ac.uk/species/Alariaesculenta.htm A1

Alaria esculenta (Linnaeus) Greville Algaebase Species Detail http://www.algaebase.org/search/species/detail/?species_id=82&sk=0&from=results

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