An encrusting cushion-like sponge known only from two locations in Northern Ireland and thought to be declining, though data is lacking.

In brief

• Found on Rathlin Island and in the Strangford Lough narrows
• Found on vertical rock faces, boulders in areas of strong water movement
• Can be found throughout the year
• A species of conservation concern because of its scarcity, and data shortage
• Main threats not known.

Species description: An irregularly shaped, relatively low-lying sponge coloured sandy, or grey-brown. It has an encrusting form, the cushion-like crust up to 7cm in diameter, and about 1.5cm thick though it becomes narrower at the margin. A somewhat shaggy or lumpy appearance is caused by cone-like projections on the surface and dark pores. The spicules (skeletal structures in the body) are pin-like, but curled.

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: The species has caused some identification problems; no less than 20 synonyms have been proposed over the years.

How to see this species: In Northern Ireland this sponge can be found off Rathlin Island and on the Lee's Wreck in Strangford Lough, both locations characterised by strong water flow. Generally it is found on vertical rock surfaces, the undersides of boulders, and despite its liking for strong currents, can also occur on boulders located in areas of stones, gravel and other sediments. Elsewhere in Ireland the species occurs quite widely in the west from Tory Island, Donegal Bay, Achill Island, Kerry Head, Sherkin Island and Lough Hyne. In Britain it is found off Anglesey, Pembrokeshire, St Kilda, and Orkney.

Current status: Known from only two locations in Northern Ireland. The species has no legal protection.

Why is this species a priority in Northern Ireland? The species is regarded as scarce, possibly declining in Northern Ireland, but it is also considered that there is inadequate data to present a true picture of its status.

Threats: Other than rarity itself, no specific threats have been documented.

Action:

• Maintain the number of viable populations
• Maintain the range
• Monitor the population (or samples) at the two known Northern Ireland 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, Holwood, 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 Strangford Lough are both designated Special Areas for Conservation under the EU Habitats Directive.

There is no Species Action Plan for Clathria barleei; however, the UK Habitat Action Plan for Inshore Sublittoral Rock contains the following provisions:

• maintain the extent and quality of inshore sublittoral rock habitats in the UK, including the full diversity of communities.

Measures to be considered further include:

• protecting sites of conservation importance from damage through contamination and physical disturbance (for example, turbidity and towed fishing gear)
• requiring EIAs for coastal developments to examine potential effects on intertidal and nearshore areas
• monitoring any impact of dump sites on inshore sublittoral rock habitats, communities and wildlife, and taking action as appropriate
• implementing strategies for managing the coastal zone at local, regional and national levels.

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

iNaturalist: Biemna variantia at iNaturalist World Species Observations database.

WoRMS: Biemna variantia at World Register of Marine Species. Accepted name: Biemna variantia (Bowerbank, 1858). AphiaID: 133205.

Literature:

Picton, B.E. and Goodwin, C.E. (2007). Sponge biodiversity of Rathlin Island, Northern Ireland. Jour. Mar. biol. Ass. UK 87: 1441-1458.

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=C5830.

Classification: Biota; Animalia; Porifera; Demospongiae; Heteroscleromorpha; Biemnida; Biemnidae; Biemna

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Allen & Mellon Environmental Ltd. (2026). Biemna variantia. (Bowerbank, 1858). [In] Priority species, Marine Biodiversity Portal NI. https://www2.habitas.org.uk/marbiop-ni/priorityaccounts.php?item=C5830. Accessed on 2026-07-28