The AWI’s new experimental facility on Sylt makes it possible to simulate the effects of climate change on coastal ecosystems.
Rising temperatures, acidification of the water, ever-increasing nutrient levels and the introduction of non-native species: humans are in the process of drastically altering the living conditions in the ocean. But what does this mean for the marine communities there? In the future, will they still be able to function as they have so far? If not, what will happen? Questions such as these can be investigated in so-called ‘mesocosms’ – large tanks filled with seawater in which various environmental factors can be varied in order to test how animals, plants and entire biotic communities react. On 5 August, the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI), opened one of Europe’s largest and most cutting-edge testing facilities of this type, in List on the island of Sylt.
“In recent years we’ve had positive experiences with such mesocosms,” says Dr Lisa Shama, a researcher at the AWI, who coordinates the facility. Back in 2013, the Institute installed a dozen of these tanks at its Wadden Sea Station on Sylt. Each tank holds 1,800 litres of seawater and can be controlled independently. This allows the precise temperature and pH value as well as the salt and nutrient content of each marine mesocosm to be precisely defined. To ensure that their inhabitants experience conditions that are as close to nature as possible, the Wadden Sea’s current and tides can also be simulated in each tank; a plexiglass lid lets in light from the outside. The AWI team has used this facility to test, among other things, the impact of various future scenarios released by the IPCC (Intergovernmental Panel on Climate Change) on marine life.
Here the focus is on the warming and acidification of the seawater, which absorbs CO2 from the atmosphere. It has been shown e.g. that amphipods living on the seafloor are particularly sensitive to changes: if the temperature and pH remain at the current level and the supply of nutrients is increased, the number of these small creatures living in the tank also increases. On the other hand, rising temperatures and higher acidity cause the amphipod stocks to collapse.
In other experiments, the AWI researchers looked into the future of the microalgae. Here, too, they found that the IPCC scenarios with higher temperatures and lower pH levels had a significant impact on the tiny algae’s world. “If we don’t slow climate change, we have to expect dramatic changes in the plankton, and therefore also in the food web,” explains Prof Karen Wiltshire, Vice Director of the AWI and Director of the Wadden Sea Station.
At the Sylt facility, bivalves, seagrass and fish have also been subjected to the warmer future conditions. For example, in an experiment with sticklebacks, Shama and her team found that environmental conditions can even have an effect on the sexual attractiveness of these small fish. In warmer mesocosms, the females prefer partners whose fathers matured in warmer waters – an indication that parent fish pass on non-genetic information to their offspring.
“However, to date we have only been able to conduct relatively simple experiments,” says the researcher. Though they certainly succeeded in manipulating two environmental parameters, like temperature and pH value, the real world isn’t that simple. “The complex ecosystems there are subject to a variety of stress factors, which also mutually influence each another,” adds Shama. Altering the nutrient supply, CO2 content and the sea level in the tanks, too, proved to be virtually impossible. After all, every combination of factors had to be run through in several tanks in order to obtain statistically meaningful results.
That’s why, in spring 2021, the AWI expanded its facility – which it christened AWISOM (‘AWI Sylt Outdoor Mesocosms’). Twelve identical mesocosms equipped with the latest technologies were added, and at the same time, the old tanks were modernised. “For example, they were given new software that can simulate the high and low tide even better,” explains Shama. “That’s especially important when it comes to investigating the effects of rising sea levels.” In addition to the 24 outdoor tanks, there are six further tanks in a giant greenhouse, which means that in future it will also be possible to conduct experiments in winter.
The first experiments in the open-air tanks are already underway. An AWI team led by Dr Tobias Dolch and Dr Ketil Koop-Jakobsen dug out blocks containing sediment and plants from seagrass beds and salt marshes in the northern Wadden Sea and transported them to twelve mesocosms. For three months the plants were exposed to the temperature and CO2conditions predicted for the year 2100.
How do the parts of the plants above and below ground develop when the water is 3.5 degrees Celsius warmer than it is today and the carbon dioxide level in the atmosphere is doubled? Does this result in changes in growth or in the mechanical characteristics of the leaves? Dolch and Koop-Jakobsen are currently investigating these questions, since, especially in the Wadden Sea, little is known about the topic to date. However, the answers will be important if we want to assess the future prospects of these ecosystems.
After all, salt marshes and seagrass beds are not only ecologically important habitats for plants and animals; they also play an important role in climate protection, since they absorb large quantities of CO2 from the atmosphere and can store a large percentage of it in the soil as carbon. It would be valuable to know what effects climate change has on these ecosystems and their carbon stores. For example, will seagrass plants still be able to successfully reproduce in the future? And will the salt marshes still retain sediment when they are flooded at high tide? Only then will they be able to adapt to the rising sea levels resulting from climate change, and to play a role in coastal protection.
“The new facility means that we will be better able to investigate these important questions concerning the future,” says Karen Wiltshire. Guest researchers from other institutions and universities have also expressed an interest in using the ‘North Sea in miniature’. After all, the future of the ocean is still full of mysteries – and perhaps some of them will be solved on Sylt.
