Stranded Seaweed on the Isle of Anglesey

Seaweed plays an important ecological role in coastal ecosystems and provide an inherent economical interest. Anglesey (Wales/Cymru, UK) is considered an ideal place for both seaweed collection and beach tourism, therefore a generalised approach to the knowledge of the stranded seaweed could be used for future plans and management. With this purpose, four west-coast and four east-coast beaches were studied over the summer. Four surveys per beach were undertaken on the stranded seaweed, and comparisons of the following parameters were made among beaches and between coasts: strandline width, coverage, biomass, species richness, diversity, evenness, occurrence and contribution to similarities and dissimilarities between and within beaches. Width was mainly affected by the beach exposure, whereas coverage was seen to be determined by the growth cycle of the inter-tidal species. No pattern in species richness, biodiversity and evenness associated to coast, currents or exposure was found. Ascophyllum nodosum, Fucus serratus, Fucus vesiculosus and Laminaria spp. were the main groups involved in the strandline differences between the geologically different West and East coasts. Storms and tourism were observed to affect the results. Two particularities were the pooling area characterised by the high accumulation of drift seaweed detected in Cable Bay, and the considerable heterogeneity in species of the White Beach strandline due to the different source communities at both ends of the beach and currents acting upon different depths. An increase of seaweed biomass was observed from June to July, corresponding to the seasonal peak in the growth cycle. Washing-up rates were calculated and used to obtain a rough estimate of annual wet weight of drift on the isle: 4,846 tonnesDryWeight year-1 (61.38-122.46 kgWetWeight m-1 year-1). Additionally, the pattern of the invasive species Sargassum muticum, found only on the West coast, was also discussed. Finally, factors contributing to the movement of seaweed along the beach were studied, by releasing tagged specimens of A. nodosum, F. serratus and F. vesiculosus and revisiting the beach 24 hours later. Marine currents were discovered to be the main factor influencing the movement, as wind and vesicles were not shown to have significant effects on the drift. This M.Sc. Thesis was awarded a Distinction.