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Warming waters

Irene Quaile
February 3, 2015

Climate change is bringing new species to a warming North Sea. While cod and shrimps move northwards, exotic immigrants are changing the ecosystem and the food chain.

An oystercatcher on Heligoland island Copyright: Irene Quaile-Kersken, DW
Image: DW/I.Quaile-Kersken

Helgoland is a tiny island edged with red sandstone cliffs, 70 kilometers (43 miles) off the German coast. It offers a window into how climate change is affecting North Sea ecosystems.

Karen Wiltshire, director of the Biological Institute Heligoland, describes the island as a lump of rock between Norway and France that rises up in the middle of a desert of sand and mud flats. Scientific observation has a long tradition there. It dates back to 1873, when Heligoland was British territory and soldiers stationed there measured water temperature and salinity. Since the 1960s, scientists have also been keeping tabs on organisms in the area.

Heating up

Over the last 50 years, conditions at Helgoland have changed dramatically. Climate change is causing wind pattern shifts and redirecting ocean currents. Scientists have registered a completely different inflow of clear, very salty water from the Atlantic into the North Sea, and the average water temperature has increased by 1.7 degrees Celsius.

That marks a much higher increase than the average in the rest of the world's oceans, Wiltshire says, which spells big changes for the island's marine ecosystem. Animals that normally would have died off after winter are surviving longer. They then eat plants as soon as they start to grow in the spring, before the plants can fully develop.

Over the last 15 years, Wiltshire and her team have also observed an influx of warm-water organisms. Researcher Heinz-Dieter Franke says DW that there are now around 60 species which were not present in local waters before, including types of hermit crabs, sea slugs, bristle worms and jellyfish. Some of the newcomers have been brought in by ships or ballast water from other areas unintentionally, but the vast majority are warmth-loving immigrants from the South or across the English Channel, Franke explains.

Karen Wiltshire Copyright: Irene Quaile-Kersken, DW
Karen Wiltshire heads the Biological Institute HeligolandImage: DW/I.Quaile-Kersken

Feasting invaders

Biologists often welcome increased biodiversity. But the impacts of climate change can create mismatches between hunter and prey or host and parasite chains, leading to a lack of food for key organisms, Franke says.

A seal near Heligoland Copyright: Irene Quaile-Kersken, DW
Climate impacts can affect the food chain up to large mammalsImage: DW/I.Quaile-Kersken

At the top of the local food chain are humans, who may have to develop new tastes when it comes to seafood. Wiltshire says some of the traditional favorites are moving out. Cod has made its way north, and local shrimp fishermen complain they have to go further afield in search of their traditional catch. That has cultural as well as economic implications for the small-scale fishing, which plays an important role in the life of coastal communities.

Concrete coastlines

Philipp Fischer, a specialist on fish ecology working at Heligoland, heads a group that is examining a different set of possible impacts of climate change on coastal eco-systems. They study the increase in severe storms and a rise in the sea level. Monitoring programs like this are important when deciding how to protect coasts. Concrete reinforcements along Japan's coasts serve as one example, Fischer says.

More than 70 percent of the German North Sea coast has also been altered. Helgoland researchers want to find out how these man-made structures affect ecological factors like fish breeding, feeding sites and, ultimately, the quality of life along coasts, Fischer says.

Concrete tetrapods along the Heligoland coast Copyright: Irene Quaile-Kersken, DW
Concrete tetrapods can block flooding and stop erosionImage: DW/I.Quaile-Kersken

Heligoland research director Wiltshire says she believes constant monitoring and long-term data of the sort collected in Heligoland are essential, "particularly when you see the rate at which new organisms are actually entering the system. At some point the carrying potential of the system will be reached; we will reach a plateau where we start to fight for space."

Wiltshire is confident that stage is still a long way off. In the meantime, she hopes humans will be able to adapt to the shifts. That could mean fishing further out, going after different kinds of fish or perhaps "even eating jellyfish," she said.