Type of fouling organism: Hydroid

Hydroids are simple in structure, all are aquatic and most are marine. The life cycle includes both sessile polyps and freely floating medusae, with hydroids formed as the sessile asexual polyp stage with a reduced pelagic free floating sexual medusae or jellyfish stage. In many hydroids, the medusa stage is reduced and remains attached to the hydroid. Some species may even have a swimming polyp stage in the life cycle.

This hydroid forms neat rounded aggregates of large polyps, which are more diffuse than Tubularia indivisa. The stems are tubular, with a yellowish coloured tegument and are branched at the base. The polyp colour is pale pink to red, and consists of a central circle of oral tentacles surrounded by paler but larger aboral tentacles. Average height is 40 - 60 mm (smaller than Tubularia indivisa) and the diameter of the polyp and tentacles is ca 10 mm. Tubularia indivisa and Tubularia larynx can be difficult to distinguish and the two often occur together. In Tubularia larynx the stems branch, while in Tubularia indivisa they are unbranched, though separate individuals settle on the stems of others forming irregular clumps.

Environment and Habitat

- Intertidal, found on rocks and algae in shallow water down to ca 25 m.
- Tolerates exposed habitats and strong water currents.
- Often seen fouling piers, boats and other structures.

Reproduction

- Reproduction type: Budding, separate sexes, vegetative.
- Reproduction frequency: Annual.
- Age at maturity: variable with change between sessile hydroid and free-living medusoid stages in the life cycle.
- Fecundity: Unknown.
- Development: Planktonic.
- Larval settlement time: Variable with life cycle change from sessile to free living.
- Dispersal potential: Unknown.
- Life span: variable, like other hydroids has the potential to be very long lived.

Communities

- Neat, bushy colonies.

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 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

- Widespread throughout the north east Atlantic and Mediterranean.

References

Tubularia larynx [In] Encyclopedia of Marine Life of Britain and Ireland P2http://www.habitas.org.uk/marinelife/species.asp?item=D1450

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.