This is a fragile encrusting sponge, known from a small number of sites, all on Rathlin Island and possibly well established there. These are the only known locations in Ireland. Whilst it appears not to have been strongly affected by bottom fisheries so far, it would be highly vulnerable if this occurred.

In brief

• Can be found on both north and south coasts of Rathlin Island
• Its habitat is bedrock, boulders grading down to gravel beds, in areas of strong current
• It can be found throughout the year
• This species is listed as an SoCC on account of the Rathlin sites being the only sites in an Irish context
• Although not currently adversely affected by bottom fishing, the species would be threatened by disruption to its habitat from this activity.

Species description: This is a thinly-formed, quite fragile encrusting sponge that grows up to about 20cm in extent. Its colour is generally yellow, sometimes quite bright, but some sources have reported a dark orange form. It has a somewhat granular appearance, with small respiratory openings and the respiratory/feeding channels are visible below its surface. The spicules (skeletal structures) are smooth, straight and have well-developed heads at one end.

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. In the case of this species it is thought that it probably releases eggs which are fertilised externally and develop into planktonic larvae (B. Picton, pers. comm.). Asexual reproduction may also be achieved by budding, whereby a small unit of the sponge separates and develops as an independent entity.

Similar species: Hymerhabdia intermedia is similar, but can be separated by examination of the spicules.

How to see this species: The only Northern Ireland sites where this species has been found are on Rathlin Island; Black Head, West of Derginan Point, to east of Sroanderrig (recorded as Damicornis Bay by researchers), and below the White Cliffs; it currently appears to be well established. It may be found on boulders and bedrock, particularly where boulders run on to more open gravel, on open sections of coast where there are strong currents. There are no other Irish records. Further afield it has been recorded as having a mainly southern distribution from Brittany, Azores and the Mediterranean.

Current status: Known only from sites on both north and south coasts of Rathlin Island. The species has no legal protection.

Why is this species a priority in Northern Ireland? The species is only known from Rathlin and is regarded as rare, though at one location it is regarded as well established. Northern Ireland holds all the Irish sites for this species.

Threats: It is considered that probably the species has not been affected by bottom fisheries so far. However, where it is found amongst boulders grading into more level gravel seabed, disruption by mobile fishing gear could threaten its survival, as like many sponges, it requires stable conditions.

Action:

• Maintain the number of viable populations of the species
• Maintain the range of the species
• Establish appropriate management of known sites
• Monitor population at a sample of Rathlin sites.

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 has been designated a Special Area for Conservation under the EU Habitats Directive.

There is no Species Action Plan for Hymerhabdia typica, but the UK Habitat Action Plan for Inshore Sublittoral Rock has the following objectives:

• 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

The Northern Ireland Habitat Action Plan for Sublittoral Sands and Gravels also applies, as mentioned above. This contains the following targets:

• maintain the extent of a representative range of sublittoral sands and gravel habitats and associated communities in Northern Ireland
• maintain the condition of a representative range of sublittoral sands and gravel habitats and associated communities in Northern Ireland.

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

iNaturalist: Hymerhabdia typica at iNaturalist World Species Observations database.

WoRMS: Hymerhabdia typica at World Register of Marine Species. Accepted name: Hymerhabdia typica Topsent, 1892. AphiaID: 132527.

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=C3840.

Classification: Biota; Animalia; Porifera; Demospongiae; Heteroscleromorpha; Agelasida; Hymerhabdiidae; Hymerhabdia

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Allen & Mellon Environmental Ltd. (2026). Hymerhabdia typica. Topsent, 1892. [In] Priority species, Marine Biodiversity Portal NI. https://www2.habitas.org.uk/marbiop-ni/priorityaccounts.php?item=C3840. Accessed on 2026-07-28