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Biological impacts of oil pollution and cleaning in the intertidal zone of exposed sandy beaches: Preliminary study of the "prestige" oil spill

Abstract:

On 13th September 2002, the oil tanker "Prestige" sunk off the Galician coast, causing one of the most important oil spills in history, which affected the entire coastline, particularly the exposed rocky shores and sandy beaches. Seventeen exposed sandy beaches were analysed along the Galician coast, in May 2003, and results were compared with previous data for September 1995 and 1996. The intertidal areas of the beaches were sampled in four tidal zones along the beach profile: swash, resurgence, retention and dry sand. Six cores of 0.05 m2 were taken at each level and washed through a 1 mm mesh. Sediment samples were collected at each level for sediment analysis. The species were grouped into six main taxonomic groups: polychaetes, molluscs, marine crustaceans, semi-terrestrial crustaceans, insects and others. The total number of species was calculated in each group before and after the oil spill. The disturbance effect on each tidal level was determined. A decrease in the species richness was generally observed in all the studied beaches, although this decrease was not homogeneous in all the taxonomic groups. Polychaetes, insects, semi-terrestrial crustaceans and others lost species in all cases, while marine crustaceans did not show this tendency, losing species in some cases and gaining in others. The most affected beaches lost up to 66.7% of the total species richness after the oil spill. The most disturbed levels were swash, losing most of the polychaetes, and dry sand, with decrease in insects and semi-terrestrial crustaceans in many cases. Dry sand level received a high amount of oil and was more affected by grooming and cleaning activities where fuel and polluted material were removed, including algal wrack that is used by the supratidal macrofauna as food and shelter.