A small red seaweed, not readily identified and rarely recorded in Northern Ireland.

In brief

• Recorded only twice in Northern Ireland at Strangford Lough and Portstewart.
• Only recorded from the sublittoral zone.
• Plants have been found only between July and November.
• This species is rare with Northern Ireland being a stronghold for the British and Irish population.
• The only threat is any change to its habitat.

Species description: A small red alga growing erect in tufts to 5cm in high. The main axis is polysiphonous and corticate with simple monosiphonous lateral branches arranged spirally around the main axes.

Life cycle: The life cycle of the three other species of Dasya is apparently the full Polysiphonia-type life history. However, D. ocellata in the British Isles reproduces only apomictically (without fertilization or meiosis) by tetraspores, borne in “stichidia” (pod-like branchlets). Male and female plants are unknown in the British Isles. However, female plants have been found in Portugal.

Similar species: There are a number of similar small filamentous algae; microscopic examination is required for identification, especially from the other species of Dasya and Brongniartella byssoides. There are four species of Dasya in the British Isles, all of which are corticate and one of Brongniartella which is ecorticate.

How to see this species: Grows epiphytically and epilithically on shaded rock to a depth of 20m on moderately exposed coasts. Only recorded between July and November, and has only been found in Northern Ireland in Strangford Lough and Portstewart. Found at extremely low water and in the sublittoral zone.

Current status: Rare. Only recorded in Northern Ireland at Gibbs Island, Strangford Lough, in 1993 (Ulster Museum: F10666) and Portstewart in 2015. Elsewhere in Ireland it has been recorded from Dublin, Wicklow, Waterford, Cork and Kerry. Northern Ireland is thought to be an Irish and British stronghold for this species.

Why is this species a priority in Northern Ireland?

• 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: Vulnerable to coastal change and damage to the sublittoral, for example, dumping of illegal waste and changes to current.

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 viable population of this species.

Conservation:

• Strangford Lough is a Marine Protected Area with multiple designations.

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

iNaturalist: Dasya ocellata at iNaturalist World Species Observations database.

WoRMS: Dasya ocellata at World Register of Marine Species. Accepted name: Dasya ocellata (Grateloup) Harvey, 1833. AphiaID: 144720.

Classification: Biota; Plantae; Biliphyta; Rhodophyta; Eurhodophytina; Florideophyceae; Rhodymeniophycidae; Ceramiales; Delesseriaceae; Dasyoideae; Dasya

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Adapted from text by Osborne Morton (2026). Dasya ocellata. (Grateloup) Harvey. [In] Priority species, Marine Biodiversity Portal NI. https://www2.habitas.org.uk/marbiop-ni/priorityaccounts.php?item=ZM10330. Accessed on 2026-09-13