The impact of extreme storm events on resilience of intertidal Fucus serratus communities
Intertidal serrated wrack Fucus serratus is common throughout the temperate N-Atlantic and plays an important role as a bioengineering species structuring lower intertidal communities. Several studies have addressed the impact of Fucus cover and its disturbance on species richness, diversity and succession of associated species in manipulative experiments. However, natural catastrophic events have scarcely been followed on a spatial mesoscale. We analyzed a 10-yrs time series on 140 permanent geo-referenced plots in the intertidal zone at the island of Helgoland (North Sea) covering an area of approx. 100 x 100 m. Samples were taken biannually in winter and summer. We describe the general intra- and interannual dynamics of F. serratus coverage and associated seaweed and mollusk species. The spatio-temporal extent and percentage coverage of F. serratus displayed a regular intra-annual pattern with lower coverage in winter than in summer whereas the spatial extent of the zone remained stable over many years. In winter 2006/2007 there was considerable loss of cover (from 100% to ≤30%), probably caused by several successive strong autumn and winter storms. Recovery of the F. serratus population required three vegetation periods. We will present data on the temporal co-variation of associated seaweed and mollusk species richness, evenness and diversity before and after the disturbance and discuss differences between investigations at different spatial scales.