Mapping and Assessment of the Seaweed Resources (Ascophyllum nodosum, Laminaria spp.) off the West Coast of Ireland

The seaweed biomass survey was designed to gather important information on those seaweed resources that are extensively harvested at present (mainly Ascophyllum nodosum) and those that offer a significant potential for future development (Laminariaceae). The first major objective of the project was to measure the intertidal biomass of Ascophyllum nodosum at selected sites along the Irish west coast. A total of 258 survey sites of varying size were selected by the survey team. They were considered to encapsulate all of the important regions where Ascophyllum nodosum harvesting was currently practiced and/or could take place in the future. Sites were selected using existing harvesting records, detailed map and chart studies and on-site visits. The total coastal area surveyed has the potential to yield 74,845 tonnes (t) of Ascophyllum nodosum sustainably per annum. The total amount harvested in 1996 was 35,850 t or some 48% of the total annual potential. The location and classification of the major Laminarian (kelp) beds off the Irish west coast was the second major objective of the project. Laminarians form the most extensive community inhabiting sublittoral rocky coasts of the North Atlantic. There are five species of the Laminariaceae and Alarinaceae families common to Irish waters, namely; Laminaria digitata, Laminaria hyperborea, Laminaria saccharina, Alaria esculenta and Sacchoriza polyschides. A process of public and private consultation, in conjunction with a number of field studies, was used to determine the distribution and relative abundance of these species on the west coast of Ireland. An estimate of the area of coastline (from Malin Head, Donegal, to Galley Head, Cork), covered by laminarians indicated that they were abundant at 22% of sites, common at 23%, scarce at 11% and absent from the remaining 44% of sites surveyed. All of the information gathered from the seaweed survey was been entered into a custom designed Geographical Information System (GIS). The system is made up of two information 'layers'. The first layer comprises a digitised outline of the Irish west coast from Donegal to Cork at a scale of 1:10,000 (6 inch to one mile). The second information 'layer' derived from data collected during the survey, comprising such details as amounts of seaweed present, harvesting details, accessibility and harvesting potential.
Funder: Marine Institute