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Intertidal blue mussel beds are important for the functioning and community composition of coastal ecosystems. Modeling spatial dynamics of intertidal mussel beds is complicated because suitable habitat is spatially heterogeneously distributed and recruitment and loss are hard to predict. To get insight into the main determinants of dispersion, growth and loss of intertidal mussel beds, we analyzed spatial distributions and growth patterns in the German and Dutch Wadden Sea. We considered yearly distributions of adult intertidal mussel beds from 36 connected tidal basins between 1999 and 2010 and for the period 1968-1976. We found that in both periods the highest coverage of tidal flats by mussel beds occurs in the sheltered basins in the southern Wadden Sea. We used a stochastic growth model to investigate the effects of density dependence, winter temperature and storminess on changes in mussel bed coverage between 1999 and 2010. In contrast to expectation, we found no evidence that cold winters consistently induced events of synchronous population growth, nor did we find strong evidence for increased removal of adult mussel beds after stormy winter seasons. However, we did find synchronic growth within groups of proximate tidal basins and that synchrony between distant groups is mainly low or negative. Because the boundaries between synchronic groups are located near river mouths and in areas lacking suitable mussel bed habitat, we suggest that the metapopulation is under the control of larval dispersal conditions. Our study demonstrates the importance of moving from simple habitat suitability models to models that incorporate metapopulation processes to

In 2005, Pacific oysters, Crassostrea gigas, were collected from May to September along the East Frisian coast and processed for histology. Because of mass mortalities in September, additional samples of moribund oysters and apparently healthy blue mussels, Mytilus edulis, were subjected to virological and ultrastructural investigation. The oysters displayed a variety of pathological conditions including viral gametocytic hypertrophy which is reported here for the first time from the German coast. Haemocyte aggregations in the digestive tract, in the intestinal mucosa and submucosa, in the mid-gut gland and in the ventricle of the heart were commonly observed at some stations. In association with mass mortalities, severe gill necrosis occurred which may have contributed to the high mortality rates. Total mortality rates of up to approximately 60% were seen. All size classes and thus age classes of oysters were affected, with highest mortality rates within the youngest age classes which had just reached sexual maturity (shell lengths <40 mm). The smallest dead oysters had shell lengths of 10 mm. The phenomenon was mainly restricted to C. gigas stocks in harbours, probably because of favourable conditions for infection, i.e. limited water exchange, less food availability, reduced oxygen content and higher pollution levels.

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Predation by herring gulls Larus argentatus and oystercatchers Haematopus ostralegus was evaluated on a newly established mussel A4ytilus edulis bed on tidal flats of the German Wadden Sea. The mussel bed covered an area of 2 ha and showed a decrease in biomass of 40 % in the most densely covered parts from August to January. Synchronously, the extent of the mussel bed was reduced, resulting in a decrease of average biomass of 98 % over the whole mussel bed. From the beginning of August 1994 to mid January 1995, the average size of mussels increased from 10.7 to 20.3 ram. The P/B-ratio was 0.68 in August and 0.18 between September and November. Herring gulls and oystercatchers were the most important mussel predators. On average, 266 herring gulls and 63 oystercatchers were present on the mussel bed during one low tide; 34 % of the herring gulls and 78 % of the oystercatchers were observed to be feeding. Herring gulls fed at a rate of 4.2 mussels per minute and oystercatchers at a rate of 1.3 mussels per minute. While herring gulls took the most common mussel sizes (mean: 20 mm), oystercatchers searched for the largest mussels available (mean: 25 ram). Herring gulls consumed 13 mussels/m 2 (0.3g AFDW) during one day and oystercatchers 1.7 mussels/m ~ (0.1 g AFDW). Predation by birds was compensated by 33 % of the production. The proportion removed by bird predation amounted to 10 % of abundance and to 16 % of biomass (including production). Oystercatchers were responsible for 1% of the reduction in abundance and for 3 % of biomass. Removal was highest in the most common size classes of mussels, mainly caused by herring gulls. However, the highest proportion of mussels was eaten in the largest size classes, mainly by oystercatchers.