A large sponge, dwelling in relatively deep water, known only from two general locations in Northern Ireland, and thought to have suffered a decline.

In brief

• Found off Rathlin Island and off the Maidens.
• Rock in depths of 40 m or deeper.
• Can be found throughout the year.
• Northern Ireland holds an important proportion of this species.
• Main threats or cause of decline are not known.

Species description: Clathria barleei is a large sponge, up to 20 cm in height and across base, coloured a dull beige, yellow or green. It has a relatively flat profile, and a porous, rather pitted appearance. There is a variety of spicules, or skeletal structures, in the body structure; some are pin-shaped, curved or straight, some have flanges, others straight but with a notable kink midway along the length.

Life cycle: Sponges have either separate sexes or are hermaphrodite. In the case of the latter, self-fertilisation is avoided by eggs and sperms maturing at different rates within the same individual, so when spawning takes place and sperms are released through exhalent openings, it is unlikely that the eggs will be fertilised. Alternatively, the eggs are retained within the sponge, and sperms drawn in from surrounding water. Fertilised eggs are released and develop into planktonic larvae. Asexual reproduction may also be achieved by budding, whereby a small unit of the sponge separates and develops as an independent entity.

Similar species: There are four synonyms, largely as a result of confusion caused by the variety of spicule types - detailed confirmation of identity can only be achieved by examination of these.

How to see this species: This sponge can be found in Northern Ireland at the south-east end of Rathlin Island and at five sites in the vicinity of the Maidens; however, it is often beyond the range of most divers, generally occurring from 40 m to depths in excess of 100 m, on rocks, boulders and stones. In Ireland it has been recorded from south Donegal Bay, Achill Island, the Aran Islands, and the outer Kenmare River. Further afield, its distribution extends from the Arctic through to western coast of France and includes Rockall and Mull.

Current status: Rare and thought to be in decline. Known from only six sites in Northern Ireland, all within either Rathlin Island or The Maidens. The species has no legal protection. Scarce in Britain and Ireland. Northern Ireland is a stronghold for this species in Ireland.

Why is this species a priority in Northern Ireland?

• Criterion 2: Decline based on available data and expert judgement.
• Criterion 3: Rare or restricted range – rare breeding species confined to 5 hectads or less (based on expert judgement).
• Criterion 4: NI stronghold or endemic – both stronghold range/population and designation as ‘endemic’ subject to expert judgement.

Threats: No threats or issues causing the suspected decline have been identified.

Action: Records of new sites for this species, with details of habitat and population are always valuable. Observations with a photograph can be recorded using iNaturalist, find the MBDP-NI iNaturalist project here.

Alternatively, records can be sent to CEDaR, National Museums Northern Ireland, 153 Bangor Road, Cultra, Holywood, County Down, BT18 0EU. Tel 028 9039 5257, e-mail cedar.records@nationalmuseumsni.org, or via the online portal.

Objectives:

• Maintain the number of viable populations.
• Maintain the range of this species.
• Establish appropriate management on appropriate historical sites.
• Consider protective measures for the Maidens locations.
• Protect sites of conservation importance from damage through contamination and physical disturbance (for example, turbidity and towed fishing gear).
• Require EIAs for coastal developments to examine potential effects on intertidal and nearshore areas.
• Monitor any impact of dump sites on inshore sublittoral rock habitats, communities and wildlife, and take action as appropriate.
• Implement strategies for managing the coastal zone at local, regional and national levels.

Conservation:

• Rathlin Island is a Marine Protected Area with multiple designations.
• There is a Habitat Action Plan for Fragile Sponge and Anthozoan Communities on Rocky Habitats and Tide-Swept Channels.
• The Maidens are a Marine Protected Area with multiple designations.

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

iNaturalist: Clathria barleei at iNaturalist World Species Observations database.

WoRMS: Clathria barleei at World Register of Marine Species. Accepted name: Clathria (Clathria) barleei (Bowerbank, 1866). AphiaID: 167498.

Classification: Biota; Animalia; Porifera; Demospongiae; Heteroscleromorpha; Poecilosclerida; Microcionidae; Microcioninae; Clathria

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Adapted from text by Allen & Mellon Environmental Ltd. (2026). Clathria barleei. (Bowerbank, 1866). [In] Priority species, Marine Biodiversity Portal NI. https://www2.habitas.org.uk/marbiop-ni/priorityaccounts.php?item=C7920. Accessed on 2026-09-13