Climate change has reached the Wadden Sea. Rising sea levels, warming, extreme weather – all of these have consequences for the world’s largest continuous sand-silt system. The Wadden Sea extends over more than 11,500 square kilometers from Denmark to the Netherlands. Around 10,000 species live here – from single-celled organisms to algae, mussels and worms to seals and porpoises. Unesco recognized the coastal area as a World Heritage Site because of its outstanding geological and ecological importance.
And then that: The World Conservation Union (IUCN) reported a year ago that the Wadden Sea World Heritage is one of the regions affected with a “very high threat” from climate change. Nevertheless, the IUCN assesses the prospects for the survival of the Wadden Sea in the foreseeable future as “good” – if the ongoing conservation and protection measures are continued.
Effects on plants and animals
which Effects of climate change on biodiversity and the geological dynamics of the Wadden Sea and what other possible protective measures can be taken is currently a topic at the 15th International Scientific Wadden Sea Symposium (ISWSS). Around 180 scientists from Denmark, Germany and the Netherlands have been discussing this in an online conference since Tuesday. A review of the event, which was originally supposed to take place in Büsum in Schleswig-Holstein, is planned for Thursday afternoon.
The scientists are focussing on the effects of climate change on birds, among other things. Millions of birds visit the Wadden Sea every year as they migrate from their breeding grounds in the Arctic to their winter quarters in Africa. According to the national park administration, the migration of migratory bird species is timed with the availability of food. “Climate change can mess up this synchronization,” it says.
A well-researched example is the knot, a wading bird that uses the Wadden Sea as a stopover on the migration route: when the chicks hatch in the arctic breeding areas, many of their food animals – small insects – are no longer available. The poorly fed young birds developed shorter beaks. As a result, as adult birds, they have disadvantages in their African winter quarters, because they poke for bottom organisms in wetlands there.
In birds that breed in the Wadden Sea, storm surges are increasingly destroying the clutches. As a result of the warming of the seas, the Wadden Sea can also now also species livewho didn’t feel comfortable here a few decades ago. But not all alien species are harmful or displace native animals and plants. New species in the Wadden Sea can have a positive impact; for example, the American razor clam serves as food for native birds. But they can also have negative consequences, for example if parasites are introduced.
According to experts from the Alfred Wegener Institute on Sylt, more than a hundred introduced alien species have settled in the Wadden Sea without driving off an original inhabitant. As a result, species and biogenic habitat diversity has increased.
Systems out of balance
A special habitat within the Wadden Sea ecosystem that the experts are focusing on are the salt marshes. These arise on flat coasts influenced by tides, when sediments are deposited there after each flood and a layer of silt forms. If this layer is thick enough, the first plants such as the samphire will settle there. However, the meadows are regularly flooded by salt water. Salt marshes are more than just a habitat for highly specialized animals and plants; according to the State Office for Coastal Protection, they protect the coast and dykes during storm surges because they dampen oncoming waves. And they serve as carbon dioxide stores.
But if temperatures rise as a result of global climate change, the system could become unbalanced. In 2018, researchers from the University of Hamburg set up dome-shaped “warming chambers” in different habitats of the salt marshes on the Hamburg Hallig, where different degrees of temperature rises were simulated. First findings from the experiment should be presented at the conference.
Incidentally, the results of the conference are to be incorporated into the ministerial declaration of the next Trilateral Intergovernmental Conference of the three Wadden Sea countries. The ministers responsible for nature conservation in the three partner countries meet every four years for a Wadden Sea conference. At their meetings, they also decide on the focus of work for the next four years. The next Wadden Sea Conference is planned for the end of 2022 in Wilhelmshaven.