Since the extent and abundance of the main Fucus cover is used as an indicator of water quality in the WFD at Helgoland and elsewhere, it is necessary to know the influence of seasonal changes in abundance and the possible restoration time after physical disturbances. The ongoing monitoring campaign started in autumn 2003 using 140 georeferenced sampling points in the northern part of the island where percentage cover of all macroalgal species is quantified in 50 x 50 cm plots revisited at each sampling date. In January 2007, a very intensive north-westerly storm most likely destroyed large parts of the Fucus serratus cover. After two years of rather consistent summer values in abundance and extent of the dense Fucus serratus beds, the mean percentage cover dropped from 100% to about 37% in February 2007, much lower than ever observed due to seasonal variation. Subsequent analysis in summer 2007 and in 2008 revealed a significant regrowth of Fucus serratus which is, however, still far from complete regeneration. Very important is the observation that understorey algae like Cladophorarupestris were not affected by the sudden removal of the top-layer and species richness remained the same. As it is the requirement of the WFD to detect changes in water quality which are not due to episodic events, continued observation of the restoration of the disturbed Fucus beds will generate the needed data. As the WFD demands values over time periods of six years, we recommend to only using the highest value observed over a six year period, thereby avoiding the strong variation due to episodic events like deleterious storms. This approach should be applied in all cases where perturbation byunusual episodic events is assumed for WFD parameters.
Helmholtz Research Programs > MARCOPOLI (2004-2008) > CO1-Coast in change