Northern Ireland's Priority Species

Dasya ocellata – a red seaweed

Dasya ocellata

Dasya ocellata (Grateloup) Harvey
Family: Dasyaceae

A small seaweed, not readily identified and only once recorded in Northern Ireland.

In brief

  • Recorded only once in Northern Ireland at Strangford Lough

  • 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 UK 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 at Strangford Lough. Found at extremely low water and in the sublittoral zone.

Current status
Only recorded once in Northern Ireland at Gibbs Island, Strangford Lough, in 1993 (Ulster Museum: F10666). Elsewhere in Ireland it has been recorded from Dublin, Wicklow, Waterford, Cork and Kerry.

Why is this species a priority in Northern Ireland?

  • It is very rare with only one record from Northern Ireland. Northern Ireland is a stronghold for the UK population.

Threats/Causes of decline
Vulnerable to coastal change and damage to the sublittoral, for example, dumping of illegal waste and changes to current.

Conservation of this species

Current action

  • Gibbs Island, Strangford Lough is designated as Ramsar site, SPA, SAC, ASSI, and MNR.

Proposed objectives/actions

  • Maintain the viable population of this species.

What you can do
Report any records to CEDaR, National Museums Northern Ireland, 153 Bangor Road, Cultra, Co. Down, BT18 0EU, [at]

Further information



Maggs, C.A. (1998). Life-history variation in Dasya ocellata (Dasyaceae, Rhodophyta). Phycologia. 37: 100–105.

Maggs, C.A. and Hommersand, M.H. (1993). Seaweeds of the British Isles. Volume 1. Rhodophyta Part 3A Ceramiales. The Natural History Museum.

Morton, O. (1994). Marine Algae of Northern Ireland. Ulster Museum.

Hardy, G. and Guiry, M.D. (2003). A Checklist and Atlas of the Seaweeds of Britain and Ireland. British Phycological Society, London.

Text written by:
Osborne Morton