Today's Wadden Sea is a heavily human-altered ecosystem. Shaped by natural forces since its origin 7,500 years ago, humans gradually gained dominance in influencing ecosystem structure and functioning. Here, we reconstruct the timeline of human impacts and the history of ecological changes in the Wadden Sea. We then discuss the ecosystem and societal consequences of observed changes, and conclude with management implications. Human influences have intensified and multiplied over time. Large-scale habitat transformation over the last 1,000 years has eliminated diverse terrestrial, freshwater, brackish and marine habitats. Intensive exploitation of everything from oysters to whales has depleted most large predators and habitat-building species since medieval times. In the twentieth century, pollution, eutrophication, species invasions and, presumably, climate change have had marked impacts on the Wadden Sea flora and fauna. Yet habitat loss and overexploitation were the two main causes for the extinction or severe depletion of 144 species ($20% of total macrobiota). The loss of biodiversity, large predators, special habitats, filter and storage capacity, and degradation in water quality have led to a simplification and homogenisation of the food web structure and ecosystem functioning that has affected the Wadden Sea ecosystem and coastal societies alike. Recent conservation efforts have reversed some negative trends by enabling some birds and mammals to recover and by creating new economic options for society. The Wadden Sea history provides a unique long-term perspective on ecological change, new objectives for conservation, 84-95 DOI 10.1007/s10152-004-0209-z restoration and management, and an ecological baseline that allows us to envision a rich, productive and diverse Wadden Sea ecosystem and coastal society.

Humans have exploited European aquatic resources since at least the Palaeolithic, but during the Middle Ages rising human populations and demand initiated great changes in many fisheries. To help understand the past and present of the Wadden Sea, this paper sets the main developments of medieval fisheries in the context of changing larger European social and aquatic environments ca. 500-1500 A.D. Anthropogenic influences on fish populations and aquatic habitats interacted with natural environmental variations. Both nutritional and cultural needs shaped human consumption of aquatic organisms. Many fisheries met the demand for food by economic reorientation from subsistence to artisanal and then even fully commercial purposes. Exploitation slowly shifted from limited or deteriorating local inland and inshore fish populations to frontier, commonly marine, and increasingly pelagic resources. Some inland regions developed aquaculture to enhance local supplies of fresh fish. General processes are illustrated by case studies of selected indicator species from freshwater and marine habitats generally pertinent to the region surrounding the Wadden Sea. Anadromous salmon (Salmo salar) and sturgeon (Acipenser sturio) were negatively affected by overfishing and by unintentional human alteration of critical habitat. Habitat preferences of catadromous eel (Anguilla anguilla) and exotic carp (Cyprinus carpio) let these species gain from medieval human activities. In the case of herring (Clupea harengus), Europe's largest early commercial marine fishery, technological innovations which raised production and consumption played off against long-term consequences of intensely exploiting sensitive natural systems.

The European bitterling is considered to be a native species over much of its present range in Europe.

Changes in climate affected human societies throughout the last millennium. While European cold periods in the 17th and 18th century have been assessed in detail, earlier cold periods received much less attention due to sparse information available. New evidence from proxy archives, historical documentary sources and climate model simulations permit us to provide an interdisciplinary, systematic assessment of an exceptionally cold period in the 15th century. Our assessment includes the role of internal, unforced climate variability and external forcing in shaping extreme climatic conditions and the impacts on and responses of the medieval society in north-western and central Europe. Climate reconstructions from a multitude of natural and anthropogenic archives indicate that the 1430s were the coldest decade in north-western and central Europe in the 15th century. This decade is characterised by cold winters and average to warm summers resulting in a strong seasonal cycle in temperature. Results from comprehensive climate models indicate consistently that these conditions occurred by chance due to the partly chaotic internal variability within the climate system. External forcing like volcanic eruptions tends to reduce simulated temperature seasonality and cannot explain the reconstructions. The strong seasonal cycle in temperature reduced food production and led to increasing food prices, a subsistence crisis and a famine in parts of Europe. Societies were not prepared to cope with failing markets and interrupted trade routes. In response to the crisis, authorities implemented numerous measures of supply policy and adaptation such as the installation of grain storage capacities to be prepared for future food production shortfalls

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