Temporal changes in community structure of tide pools following the “

The impact of the “Erika” oil spill on the tidal rock pool community, and particularly on two species of sea urchin (Paracentrotus lividus and Psammechinus miliaris), was investigated over a 3-year period, at Piriac-sur-Mer (Department of Loire-Atlantique, France, 47°21.6' N; 2°31.7' W). A dramatic increase in the abundance of two macroalgae Ulva sp. and Grateloupia doryphora occurred following a 100% mortality of sea urchins observed three weeks after the oil spill. The density of sea urchins and of other main herbivores, the periwinkle Littorina littorea and the trochid mollusks Gibbula umbilicalis and Gibbula pennantii, were monitored between January 2000 and March 2003. There was significant inverse relationship between the overall density of herbivores (sea urchins, periwinkles and trochid mollusks) and the percent cover of algae in the tidal pools. The first urchins in the tidal pools were observed two years after the oil spill and it took three years to reach sea urchin densities comparable to the reference value of 63 ind.m−2 obtained before the oil spill.