The intertidal areas of the Howth Peninsula
by Gill Weyman
During the summer of 1997 I carried out an intertidal survey
of the Howth Peninsula and Ireland's Eye as part of a Master of
Science Environmental Sciences research project at Trinity College,
Dublin. The results contributed towards a report on the nature and
conservation value of the area by consultants NRDC (Natural
Resources Development Centre), as part of the process of an
application for a Special Area Amenity Order by Fingal County
Council.
Seventeen sites were assessed to determine the number, abundance and distribution of species living between the low and high tide marks. The sites were chosen according to habitat type, accessibility, aspect, and wave exposure. At each site number of species was identified and their abundance noted according to biotope. A biotope is defined as the environmental (physical) habitat together with its community of species.
The results from the survey found that the intertidal areas are ecologically very complex, being dynamic and in a constant state of change. Many marine species are opportunistic and colonise only when there is a suitable substrate, adequate protection, and available food. Enteromorpha sp. is such a species, found on the freshwater outfalls at the Sutton mudflats or in the highly enriched nutrient rock pools from the seabird colonies on Ireland's Eye. Using number of species as an indicator of conservation value must be treated with caution when comparing the ecology. Not only are biotopes a relatively new method of marine classification but there is still a considerable amount of knowledge to be gained on marine species themselves.
A total of 97 species were found in the survey area. The highest number of species was found in the south western part of the Howth Peninsula to the south west of the Baily Lighthouse, probably due to the sheltered rocky inlets and readily available food to be found there.
Rocky shores are richer than other shorelines in number of species because of the availability of a suitable substrate for species such as algae, seaweeds, barnacles and limpets to attach themselves to. Coarse and gravel shores were found to be lacking in species because an unstable coarse substrate is unsuitable for burrowing.
Red algae were dominant on exposed zones such as the area directly north east of the Baily Lighthouse. Comparison of data from this survey found that the Howth peninsula and Ireland's Eye are clearly important for their number and abundance of brown and green algae rather than red algae. The zones of algae and other species are often obvious and can be seen from a boat and parts of the cliff line.
Although no rare species were found, the methods used suggest that Howth is unique to the eastern coast in terms of species richness. Thirty six biotopes were recorded, fifteen of which could be compared to similar sites in Ireland. Of these fifteen, over fifty percent had a higher number of species than similar biotopes.
The nutrient content of Dublin Bay will have an effect on species numbers and abundance, and this survey could be used as a baseline for future study. After 1998, legislation requires sewage effluent to undergo secondary treatment and the discharge pipe off the nose of Howth combined with the south to north flow of currents may well have an impact on the intertidal ecology of the surrounding area.
The area is ecologically important and of great value for educational and scientific purposes, with a wide diversity of species present within a relatively small area. The area is vulnerable due to recreational and commercial uses, and the closeness of Dublin with its relatively high population density. It is therefore important that it is managed so that its development does not result in loss of diversity, or detriment to the intertidal ecology.
© Gill Weyman, 1997.
Acknowledgements: Dr Jim Wilson, Environmental Sciences Unit, Trinity College; Natural Resources Centre, Trinity College; BioMar, Trinity College; Maurice and Joe McDermot, Howth; and the Commissioners of Irish Lights
Seventeen sites were assessed to determine the number, abundance and distribution of species living between the low and high tide marks. The sites were chosen according to habitat type, accessibility, aspect, and wave exposure. At each site number of species was identified and their abundance noted according to biotope. A biotope is defined as the environmental (physical) habitat together with its community of species.
The results from the survey found that the intertidal areas are ecologically very complex, being dynamic and in a constant state of change. Many marine species are opportunistic and colonise only when there is a suitable substrate, adequate protection, and available food. Enteromorpha sp. is such a species, found on the freshwater outfalls at the Sutton mudflats or in the highly enriched nutrient rock pools from the seabird colonies on Ireland's Eye. Using number of species as an indicator of conservation value must be treated with caution when comparing the ecology. Not only are biotopes a relatively new method of marine classification but there is still a considerable amount of knowledge to be gained on marine species themselves.
A total of 97 species were found in the survey area. The highest number of species was found in the south western part of the Howth Peninsula to the south west of the Baily Lighthouse, probably due to the sheltered rocky inlets and readily available food to be found there.
Rocky shores are richer than other shorelines in number of species because of the availability of a suitable substrate for species such as algae, seaweeds, barnacles and limpets to attach themselves to. Coarse and gravel shores were found to be lacking in species because an unstable coarse substrate is unsuitable for burrowing.
Red algae were dominant on exposed zones such as the area directly north east of the Baily Lighthouse. Comparison of data from this survey found that the Howth peninsula and Ireland's Eye are clearly important for their number and abundance of brown and green algae rather than red algae. The zones of algae and other species are often obvious and can be seen from a boat and parts of the cliff line.
Although no rare species were found, the methods used suggest that Howth is unique to the eastern coast in terms of species richness. Thirty six biotopes were recorded, fifteen of which could be compared to similar sites in Ireland. Of these fifteen, over fifty percent had a higher number of species than similar biotopes.
The nutrient content of Dublin Bay will have an effect on species numbers and abundance, and this survey could be used as a baseline for future study. After 1998, legislation requires sewage effluent to undergo secondary treatment and the discharge pipe off the nose of Howth combined with the south to north flow of currents may well have an impact on the intertidal ecology of the surrounding area.
The area is ecologically important and of great value for educational and scientific purposes, with a wide diversity of species present within a relatively small area. The area is vulnerable due to recreational and commercial uses, and the closeness of Dublin with its relatively high population density. It is therefore important that it is managed so that its development does not result in loss of diversity, or detriment to the intertidal ecology.
© Gill Weyman, 1997.
Acknowledgements: Dr Jim Wilson, Environmental Sciences Unit, Trinity College; Natural Resources Centre, Trinity College; BioMar, Trinity College; Maurice and Joe McDermot, Howth; and the Commissioners of Irish Lights