Site Description of "Thumb Rock" at Mullaghmore:

Habitat / Substrate and Biotope / Faunal Community


Project description

Marine Biodiversity and Ecology Research at Mullaghmore Co. Sligo, to aid Environmental Protection of this unique ecosystem; with Sub aqua Web site Development for the Institute of Technology, Sligo.



The Mullaghmore headland is situated on the Sligo coast towards the boarder with Leitrim, on the South of Donegal Bay. The Grid Reference is G 70 60. It is predominantly composed of Mullaghmore sandstone which was laid down about 1500 million years ago. The rock is tilted, often giving a vertical face on one side and a gentle slope on the other. This variation has implications for marine life. The numerous cracks and crevices in the rocks also provide flora and fauna with the variation required for a high biodiversity.

Mullaghmore Geology

The village of Mullaghmore is situated beside the harbour on the eastern side of the headland. The village includes two hotels, a restaurant, a shop and numerous houses. A community septic tank was constructed in the mid 1960 to serve the village. The system works without a percolation area as the effluent is piped straight to the sea at G711 579. The effluent is released on a continuous flow basis - as waste water enters the system, effluent is released. Thus, in reality the system is no more than a primary settlement facility. Since its installation in the 1960s, numerous housing developments, primarily holiday homes and villages have been connected to the "sewage system". The new developments have introduced a significant seasonal variation while increasing flow substantially.

An area adjacent to the outflow of the pipe is a popular dive site (marked Thumb Rock (1) on Map ). Hailes (1994), in the Underwater Ireland, Guide to Irish Dive Sites, notes the presence of the sewage outfall. He states that "at certain stages of the tide, and especially when the village is busy, sewage can be encountered close to the shore to the south of Thumb Rock There is evidence of some pollution on Thumb itself in the form of a dusty like deposit."

Biomar field notes (unpublished) describe the sublittoral around Thumb Rock - A moderately exposed, sheltered seabed to the east of a large headland. There was a stepped limestone platform from 18-22m BCD.

Scientists Associated with BIOMAR :

Bernard Picton

Mark Costello



Conner et al (1997) in Marine biotype classification for Britain and Ireland, volume 1. Littoral biotypes and volume 2 sublittoral biotypes Link attempt to provide a tool to aid management and conservation of marine habitats. Biotype is taken as the habitat together with its recurring associated community of species, operating together at a particular scale. Habitat is taken to include substratum, wave exposure, salinity, tidal streams and other factors which contribute to the overall nature of the location. Community is taken to indicate a similar association of species which regularly recurs in widely separated geographic locations. Degree of similarity will depend on the scale.

The areas around the pipe and Thumb Rock can be classified as followes - In general terms..consists of two main Biotopes: MIR.Lhyp and in deeper water, ECR.AlcC

The diversity at this site is very high. This is a popular dive site for divers from all around Ireland. The sea fan Eunicella verrucosa and the sea cucumber, Holothuria forskali, are abundant, but, based just on impressions while diving, the former appears to be decreasing in abundance and the latter appears to be increasing in abundance. Data should be collected to check out this. The former is fragile and could be inadvertantly damaged by divers and the latter is a deposit feeder, which might initially thrive on outflows from the pipe, at low nutrient levels. A B.Sc.(Hons) in Environmental Science and Technology Project, undertaken at the Institute of Technology, Sligo, by Damian Allen, and supervised by Dr. Bill Crowe, looked at the distribution of total bacterial counts and coliform bacteria in the gut of Holothuria forscali found adjacent to the sewage disposal pipe. Sampling for the project only took place between December 1997 and February 1998 and low levels of bacteria were found. However, the situation may be different in summer months, when the population of tourists visiting and living in the region increases dramatically, adding pressure to the sewage disposal system. Polymastiid sponges are common and diverse. Potential human impacts in the area are noted as the sewage disposal, sea angling and potting.

Thumb Rock at Mullaghmore has been chosen by Biomar as an important marine site in Ireland, just across Donegal Bay from St John's Point, another important site, also chosen by them and also a DUCAS site.

DUCHAS, Ireland (1: English and Gaelige (Irish) options) : The National Parks and Wildlife Service of Duchas (The Heritage Service) Their new web site allows one to download digital maps of the various nature conservation areas (Natural Heritage Areas (NHA), Special Areas of Conservation (SAC), Special Protection areas (SPA), etc.) on county by county basis. Access to much of the information at this site requires the use of a GIS package.
DUCHAS, Ireland (2: English Version only) : The National Parks and Wildlife Service of Duchas (The Heritage Service) Their new web site allows one to download digital maps of the various nature conservation areas (NHA, SAC, SPA etc.) on county by county basis. Access to much of the information at this site requires the use of a GIS package
DUCHAS, Ireland (3) : The National Parks and Wildlife Service of Duchas (The Heritage Service) Contains information on the Heritage of Ireland, including historic sites, parks and gardens, inland waterways, and natural cultural institutions.

Thumb Rock has been characterised By Biomar in a couple of once off surveys. Now it should be studied on a continuous bases; monitored over as long a time frame as possible.

The project will aim to be in line with current policies of: Europa: The European Commission: Integrated Coastal Zone Management (This link contains links to two documents on coastal zone management: 1. A Communication from the Commission to the Council and the European Parliament on "Integrated Coastal Zone Management: A Strategy for Europe" 2. A proposal for a European Parliament and Council Recommendation concerning the implementation of Integrated Coastal Zone Management in Europe)

Recently, Mick O’Rourke has started an excellent Irish Underwater Council (C.F.T.). Web Site

Information on marine or environmentally orientated web sites.


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