Wadden Sea

Category: Marine and Oceanic Biomes.

Geographic Location: Europe.

Summary: Crucial to the migration of nearly 12 million birds and host to thousands of other native species, this ecosystem has been upset by increased ecotourism and the effects of aquaculture here.

Situated in the southeastern North Sea, the Wadden Sea is one of the largest and most naturally thriving intertidal zones in the world. The word wad in Dutch translates to “mud flat,” the defining characteristic of this area. This intertidal zone ranges from the banks of the Netherlands, Germany, and Denmark to the northwestern Frisian Islands (also known as the Wadden Islands), an archipelago of barrier islands that separates the Wadden from the North Sea. The Wadden Sea covers a total area of approximately 3,900 square miles (10,100 square kilometers), and has about 310 miles (500 kilometers) of coastline.

The chain of Frisian Islands, of which there are approximately 50, was formed some 7,000 years ago, making this isolated sea one of the youngest bodies of water in the world. Even as recently as 1,000 years ago, the barrier islands underwent significant erosion that detached them from the mainland, truly making them a group of islands and defining the Wadden Sea from the North Sea.

Furthermore, the landscape of the sea is constantly changing. The turbid sea and wind of both the North and Wadden Seas actively remove and deposit sediment from sandbars and islands over many years, causing the layout of the islands and water channels to vary over short time scales. The general movement of the islands is from west to east.

The climate in the region is mainly temperate and marine, with cool summers and mild winters. The average temperature ranges from 34 to 41 degrees F (1 to 5 degrees C) in January and from 55 to 72 degrees F (13 to 22 degrees C) in July. It rains throughout the year, and extreme cold is rare.

Biodiversity

Because of daily tide cycles and easy access to its mudflats, the Wadden Sea is an important research site for studying organismal adaptation to changes in salinity, populations of benthic micro- and macroorganisms, and shorebird behavior. It is estimated that more than 10,000 species rely on this ecoregion for all or part of their life cycles. At the center of the ecosystem are the microorganisms, which are critical to nutrient cycling and largely dominated by mudflat bacteria. Despite a troubled history of aquaculture, mollusks continue to play an important commercial and ecological role in the sea; more than 27,000 tons (24,500 metric tons) of blue mussels (Mytilus edulis) are harvested annually for commercial purposes. However, harvests are closely monitored because of the reliance of multiple shorebird species on the blue mussel.

The Wadden Sea has been named one of the top 100 birding sites in the world. In addition to the permanent shorebird populations here, the mudflats are a critical habitat for more than 50 species of migratory birds. This makes the area one of the largest migratory bird habitats in western Europe. The region is a crucial element of the East Atlantic Flyway; an estimated 12 million birds migrate to the Wadden Sea every year.

An incredible array of bird species can be found on the mudflats and dunes of the coast and islands, including the pied avocet (Recurvirostra avosetta), osprey (Pandion haliaetus), barnacle goose (Branta leucopsis), sandwich tern (Thalasseus sandvicensis), and bar-tailed godwit (Limosa lapponica). Other birds of note include the spoonbill, eider, ringed plover, oystercatcher, and the peregrine falcon.

The rich diversity of the islands and marshes also makes the Wadden Sea an attractive migratory location. More than 900 species of plants, 300 mosses, 650 fungi, and 350 lichens are found in and around the sea and the islands. Some areas of the sea boast an abundance of 2.2 pounds (1 kilogram) of shorebird food per 11 square feet (1 square meter).

This ecosystem is also home to large marine mammals, including the harbor seal, the gray seal, and the harbor porpoise. These animals can avoid predators in the shallow, warm water of the sea, and the seals use the sandbanks for nursing their young. Additionally, the strong water currents and daily tides in the region provide the Wadden Sea approximately 20 times more nutrients than the adjacent North Sea, allowing this ecoregion to sustain its incredible diversity.

Human Impact

Like many waterways, the Wadden Sea has been significantly affected by chemical and agricultural runoff from the mainlands and increased turbidity from mainland diking. In the 1960s, shorebirds that relied on the shallow waters of this area for fishing experienced population declines when the water became too polluted from chemical runoff. In the mid-21st century, the sea also became used for aquaculture, which resulted in a continuous disturbance of the sea floor and increased turbidity. Besides pollution, recent studies suggest that climate change has influenced and will continue to influence the migration of birds to the Wadden Sea. Some scholars suggest that the shoreline is one of the most human-modified environments in the world.

The Wadden Sea became a tourist destination for many Europeans in the 19th century, when several of the islands opened resorts. Since then, more than 1.8 million visitors per year have had the opportunity to hike on the mudflats during low tide to observe shorebirds and invertebrates. Because of the increased boating and mudflat hiking in the region, the Learning Center of the Wadden Sea (Schutzstation Wattenmeer), operated by the German government, has established various conservation areas (Schutzzone) throughout the zone and has initiated research to ensure the protection of critical mudflat species.

Many of the islands continue to be occupied by residents today. Hallig Hooge, the second-largest halligen (German island), had a 2021 population of 95 residents living on 10 terpen, which are artificially formed mounds where homes and businesses have been built. These mounds are similar to compact neighborhoods. Some mounds host smaller structures, such as the local school and church, whereas the hallig nature center, movie theater, gift shop, grocery store, and various cafes are located on a larger mound.

These terpen are essential for hallig living, because the smaller islands experience annual floods that would otherwise destroy homes and businesses. Additionally, some of the homes and businesses on the terpen are remarkably sustainable, using geothermal and solar energy for their main sources of heat and electricity. Because the low-lying areas of the island are used for research, tourism, and cattle rearing, residents do have to visit the mainland for specialty items or bulk food.

The Wadden Sea is a remarkably diverse habitat, and is considered to be one of the last pristine intertidal zones in the world. The International Union for Conservation of Nature and Natural Resources (IUCN), an international conservation organization, has characterized the sea as a Category II national park. This recognizes the immense value of this area for its contribution to ecosystem processes and educational, scientific, and cultural enrichment.

In June 2009, the Dutch and German portions of the sea were placed on the World Heritage Site List by the United Nations Educational, Scientific, and Cultural Organization (UNESCO). The list denotes places or objects of cultural or natural significance around the world, furthering protection for the region. Since its induction in 2009, the area’s perceived threat for ecological harm has remained at zero.

In 2005, an annual Wadden Sea Day was established as an opportunity for researchers, educators, and conservationists to meet and discuss important ecological trends in the region. The 2022 Wadden Sea Day, entitled “Who Eats Whom?” focused on the relationship of the organisms within the region’s food chain. In 1997, Germany, Denmark, and the Netherlands signed the Trilateral Wadden Sea Plan to ensure shared management and protection of the sea by the three countries. Following this plan in 2002, they developed the Wadden Sea Forum to oversee the conservation of the sea and monitor the protection status of the region.

Bibliography

De Jonge, V. N., K. Essink, and R. Boddeke. “The Dutch Wadden Sea: A Changed Ecosystem.” Hydrobiologia 265, nos. 1–3 (1993).

“Hallig Hooge.” City Population, 31 Dec. 2021, www.citypopulation.de/en/germany/schleswigholstein/nordfriesland/01054050‗‗hallig‗hooge/. Accessed 18 Aug. 2022.

United Nations Educational, Scientific, and Cultural Organization (UNESCO). “The Wadden Sea.” World Heritage Centre. http://whc.unesco.org/en/list/1314.

Van Beusekom, Ruud, Nick Langley, and Manon Tentij, eds. The Wadden Sea: A Vision for the Conservation of a Natural Heritage. Cambridge, UK: BirdLife International, 2009.

Vollmer, M., M. Guldberg, M. Maluck, D. Marrewijk, and G. Schlicksbier. “Landscape and Cultural Heritage in the Wadden Sea Region: Project Report.” Wadden Sea Ecosystem 12 (2001).

“Wadden Sea Day 2022: Who Eats Whom?” Wadden Sea World Heritage, 2022, www.waddensea-worldheritage.org/events/wadden-sea-day-2022. Accessed 18 Aug. 2022.