Human transformations of the Wadden Sea ecosystem through time: a synthesis

Abstract

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.

Extinctions in ancient and modern seas

“…Several species have reached such low abundance that they can be considered ecologically, functionally, or economically extinct. However, not all local extirpations are permanent and some have been reversed by natural or assisted reintroduction [34,35]. Whether global or local, ecological, or economical, extinctions and extirpations often have strong consequences for the ecological structure and resilience of marine ecosystems as well as for ecosystem functions and services to human well-being [34,36,37].…”

“…have particularly strong effects on associated species. In the Wadden Sea, for example, loss of such habitat contributed to 70% of the 25 species extirpations in historical time [34]. In the fossil record, the loss of shallow marine habitat due to falling sea level has been associated with elevated extinction rates [13] and biodiversity loss [49].…”

“…Global warming and ocean acidification, which are of growing concern today and for the future [3,4,38], were important factors in some ancient extinctions [27,28] but played little role in historical extinctions (Table 1, Box 2) [11,33,34]. Geochemical and paleontological evidence suggests that four of five global reef crises and three of five mass extinctions in the fossil record were associated with warming and acidification ( …”

“…There is great uncertainty about how these cumulative impacts will interact to affect marine species and ecosystems; if already severely stressed, their resilience to further change can be greatly reduced [8,61,62]. Historical assessments show that multiple human impacts were involved in approximately 40% of extirpations in the Wadden Sea [34] and 42% of extirpations in estuaries and coastal seas worldwide [33]. This usually involved the combination of overexploitation and habitat loss and, to a lesser extent, pollution.…”

Nonnative macrobenthos in the Wadden Sea ecosystem

“…When 7,500 years ago sea level rise slowed down, barrier islands, extensive sediment flats, salt marshes and estuaries did evolve in roughly the present position . During the last thousand years, most salt marshes have gradually been converted into arable land, small estuaries into freshwater streams, large estuaries into shipping canals, and many soft shores into artificial hard shores (Lotze et al, 2005). Still, this coastal region is characterized by the largest coherent tidal flats on earth, attracting huge flocks of foraging birds and young fish from the North Sea.…”