Consequences of climate change on land and at sea are increasingly changing the ecosystem in the Wadden Sea, a UNESCO World Natural Heritage site, on various levels. This emerges from a new quality status report on climate change that the Trilateral Wadden Sea Secretariat in Wilhelmshaven recently published.
Changes can be observed in sea level, temperatures and the occurrence of extreme weather events, said Julia Busch, climate change program manager at the Wadden Sea Secretariat, to the German Press Agency. “If important elements in this well-oiled system are missing or shifted, this has an impact on the entire system.” In addition, there is human use of the Wadden Sea, for example for fishing and tourism.
Researcher: “Unprecedented changes” in the Wadden Sea
Since the publication of the last status report on climate change in the Wadden Sea in 2017, “unprecedented changes” have been observed in the Wadden Sea, the report’s lead author, Katja Philippart, a scientist at the Royal Netherlands Institute for Marine Research (NIOZ), is quoted in a statement from the Wadden Sea Secretariat. These included a mass die-off of cockles as a result of a heat wave in 2018, a decline in freshwater flow from rivers into the North Sea and a rise in sea levels.
It is urgently necessary to take coordinated measures to combat the effects of climate change on the Wadden Sea. “Finding ways to give the ecosystem more time to adapt to these aspects of climate change will be a major challenge for everyone involved in monitoring, research and management of the Wadden Sea,” said Philippart.
The environmental organization WWF was alarmed by the new report. “The report confirms WWF’s fears that climate change is the greatest threat to the Wadden Sea,” said the head of the WWF Wadden Sea office in Husum, Hans-Ulrich Rösner. Flooded mudflats and the breaking off of individual islands as a result of accelerated sea level rise could lead to long-term destruction of the Wadden Sea. “Only global climate protection can slow excessive sea level rise, but additional climate adaptation measures are also necessary so that the Wadden Sea can grow higher with sea level,” said Rösner.
Temperature record in the western Wadden Sea
As a result of global climate changes, scientists are also registering temporary increases in air and water temperatures in the North Sea region. The study authors point out that the highest sea water temperature in 160 years was measured in the western Wadden Sea last June at 18.5 degrees.
Some species can adapt well to higher temperatures, others less so, Busch said. “We are already seeing a change in the species composition.” Scientists have long been concerned that the flight and resting times of migratory birds are changing. The report cites the example of black-tailed godwits, which have to shorten their rest in the Wadden Sea in order to catch up with the earlier hatching of insects that serve as a food source in their breeding area of Siberia, caused by global warming.
The report also refers to a study according to which the lugworm could also move north as a result of climate change and so its occurrence could decline.
Rivers transport less fresh water to the Wadden Sea
The Wadden Sea is also feeling the effects of climate change on land, for example through increased consumption of freshwater resources on land, said Busch. “This is a point that has perhaps received little attention so far.” An example is changes in salinity. The less fresh water comes into the salty Wadden Sea, the higher the salinity remains, said Busch. The water is therefore less diluted.
Since spring and summer were drier and warmer on average recently, rivers such as the Ems, Elbe and Weser discharged less fresh water into the Wadden Sea. “This affects the life of algae and therefore also of fish and birds in the mud flats,” explained Philippart. Fresh water contains phosphate and nitrogen, which serve as the basis for algae growth and the food chain.
Heat wave hits cockles
Extreme weather events such as heat waves are also likely to become a problem for life in the Wadden Sea, write the study authors. Philippart refers to the large die-off of cockles in the Dutch Wadden Sea in the summer of 2018. “In addition to the heat, this probably also had to do with the decline in the supply of freshwater algae as a food source for these mussels.”
The new report is part of a collection of reports that reflect the assessment of the ecological status of the Wadden Sea. Other status reports, which are also regularly updated, deal with species and environmental pollution. Scientists from all three states bordering the Wadden Sea, Germany, Denmark and the Netherlands, worked on the new report on climate change.
