Northern Ireland holds a large number of sites with this sea squirt, which otherwise is regarded as rare. It is threatened by bottom fishing operations, and may have declined as a result of this.

In brief

• Found at a number of sites from Rathlin Island through to St John’s Point, Dundrum Bay
• Habitat is silty areas with moderate shelter
• Can be found throughout the year
• Regarded as a species of conservation concern because of likely decline in recent years
• Main threats are from use of mobile fishing gear.

Species description: This is a solitary and somewhat inconspicuous sea squirt; however, its distinctive form prevents confusion with other species. It is grey or grey-brown in colour, globule in shape, up to 4cm height, and is covered with branched hairs or spine-like projections, each with its own array of four to eight secondary spinelets. These trap silt, partly causing the colour. The siphons (inhalant and exhalant openings for feeding and respiration) are short and sometimes fringed with a reddish colour.

Life cycle: Settlement and recruitment take place throughout the year.

Similar species: None.

How to see this species: This is a northern species, found from the Arctic through Norway and Sweden, around Scotland. The only sites in Ireland are in Northern Ireland, at Rue Point on Rathlin, Murlough Bay, the Maidens, Muck Island, the Copeland Islands, the Long Sheelagh in Strangford Lough and off St John’s Point in Dundrum Bay. It may be found in silty areas of moderate shelter, though elsewhere in its range, more exposed sites have been reported.

Current status: Present at a range of sites around the Northern Ireland coast. The species has no legal protection.

Why is this species a priority in Northern Ireland? This sea squirt is regarded as rare, and Northern Ireland holds all the Irish locations, according to current information. It is likely to have declined in recent years due to disruption of its seabed habitat.

Threats: The main threat is disruption of its seabed habitat by the use of mobile bottom fishing gear, trawling or dredging for scallops or Nephrops. The former is particularly known to be the case in Strangford Lough.

Action:

• Maintain the number of viable populations
• Maintain the range
• Establish appropriate management on appropriate historical sites —notably Strangford Lough, but also investigate other locations where damage is likely to have occurred
• Monitor populations (or samples) at appropriate key locations.

Objectives: Records of new sites for this species, with details of habitat and population are always valuable. Send these to CEDaR, National Museums Northern Ireland, 153 Bangor Road, Cultra, Holywood, County Down BT18 0EU. Tel 028 9039 5257 or e-mail cedar.info [at] nmni.com. If you are a diver, and interested in becoming involved in recording marine life in Northern Ireland through the Seasearch project, contact Claire Goodwin at claire.goodwin [at] gmail.com or look at the web site www.seasearch.org.uk (Northern Ireland web pages).

Conservation: Survey work is being conducted throughout Northern Ireland waters (including the north coast) by Northern Ireland Environment Agency for this and other species and habitats generally.

Rathlin Island and its waters, and Strangford Lough are designated as Special Areas for Conservation under the EU Habitats Directive. Strangford Lough is the subject of a restoration project to restore the Modiolus modiolus community, and this is likely to benefit this sponge as it colonises shells of M. modiolus and other associated epifaunal.

There is no Species Action Plan for this species, but the Habitat Action Plans for Inshore Sublittoral Sediment (UK), and the Northern Ireland Habitat Action Plan for Modiolus modiolus beds apply. The latter has the following provisions:

• maintain the extent of M. modiolus beds in Northern Ireland
• where appropriate, maintain the area of M. modiolus beds in favourable condition
• by 2020, improve the condition of as much as is practical, of the 1200ha of M. modiolus beds currently in unfavourable condition within Strangford Lough.

Distribution Map from NBN: Boltenia echinata at National Biodiversity Network mapping facility, data for UK.

iNaturalist: Boltenia echinata at iNaturalist World Species Observations database.

WoRMS: Boltenia echinata at World Register of Marine Species. Accepted name: Boltenia echinata (Linnaeus, 1767). AphiaID: 103814.

Literature:

Picton, B.E. and Morrow, C.C. (2007). [In] Encyclopedia of Marine Life of Britain and Ireland.

http://www.habitas.org.uk/marinelife/species.asp?item=ZD2300.

Svane, I. and Lundälv, T. (1982). Population dynamics and reproductive patterns of Boltenia echinata (Ascidiacea) on the Swedish west coast. Neth. Jour Sea Res. 16: 105-118.

Classification: Biota; Animalia; Chordata; Tunicata; Ascidiacea; Stolidobranchia; Pyuridae; Boltenia

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Allen & Mellon Environmental Ltd. (2026). Boltenia echinata. (Linnaeus, 1767). [In] Priority species, Marine Biodiversity Portal NI. https://www2.habitas.org.uk/marbiop-ni/priorityaccounts.php?item=ZD2300. Accessed on 2026-07-28