Aarhus University Seal

Research and consultancy projects

The Danish Centre for Wadden Sea Research is involved in a wide range of research and consultancy projects that are carried out with both national and international partners.

Blue carbon potential in the Wadden Sea

Salt marsh – a "blue carbon" habitat. / Photo: Elizabeth Graversen ©

The Wadden Sea contains many habitats that absorb and store carbon (blue carbon). It is well-known that seagrass meadows and salt marshes store organic carbon in the seabed, but there is limited documentation of this potential in the Wadden Sea. Moreover, it remains unclear to what extent it is possible to increase the blue carbon potential of the Wadden Sea through protection and restoration of the habitats. There is also an unknown potential for carbon storage on the wading surfaces without vegetation, and knowledge about the role of the fauna is lacking. In addition to functioning as carbon storage, ' blue carbon ' stimulates habitats, biodiversity, retains nutrients and constitutes natural coastal protection. Sustainable management of the habitats therefore includes marine tools with effects on climate, biodiversity and water quality. We build knowledge that can contribute to better management of the blue carbon habitats of the Wadden Sea with a view to optimising carbon burial, biodiversity, etc.

From Aarhus University, we also collaborate on blue carbon with colleagues at other universities, including the University of Southern Denmark.


Sustainable seal tourism in the Danish Wadden Sea – Development of a ' Code of Conduct ' for tourist activities

With seals as an important attraction, the Wadden Sea has experienced an increasing number of tourists. The Wadden Sea is an essential habitat for both the harbour seal and the grey seal, and it is therefore crucial for the preservation of the seals in the Wadden Sea that all activities take place in a sustainable manner. There is very limited knowledge about the actual impact of disturbances on the seals, and both managers and tourist operators want research-based guidelines for seal tourism in the Wadden Sea.

Controlled experiments, drone recordings and satellite marking of seals will be used to study the effect of the tourism on the seals ' behaviour.


Coastal squeeze and loss of coastal bird habitats

Rising sea levels pose a threat to many coastal habitats and, thus, to the habitats of shore birds that depend on them. The Danish coasts in general, and the Wadden Sea coasts in particular, are particularly vulnerable, as the majority have dykes to protect human interests on land. These dykes prevent the coastal habitats from wandering inland as the water rises and causes shallow areas, mud surfaces and marshes to be at risk of flooding – a phenomenon known as coastal squeeze.


Changes in the Wadden Sea driven by invasive species and climate change

The Wadden Sea ecosystem is undergoing changes as a result of both invasive species and climate change.  Pacific oysters are a significant cause of this development. As a reef-forming species, they are ecosystem engineers that have a significant influence on flora and fauna, and they have helped establish several new species. Among other things, the two new crab species in the Wadden Sea - Asian shore crab and brush-clawed shore crab - seem to have been favoured by oyster reefs.  Both Pacific oysters and shore crabs constitute a possible threat to blue mussels and, thus, to the habitat type blue mussel beds represent. The present research area focuses on identifying the significance of the new species for biodiversity and for the Wadden Sea food network – including the consequences for birds and fish.


The distribution of resting shorebirds and their food consumption in the Wadden Sea in relation to the tidal cycle and sediment

The Wadden Sea is a dynamic intertidal area with great differences between ebb and flow, which means that the different bird species must adapt to changing conditions. The studies analyse the distribution of the common wading bird species and their foraging activity on the tidal surfaces in relation to the tidal rhythm, sediment and the distribution of prey. In addition, the species' adaptation to changed sediment conditions caused by climate change is assessed.  


Karsten Laursen, Senior Researcher emeritus

Phyto and Microzooplankton, e.g. in the Wadden Sea

In connection with the project "Reprocessing of phytoplankton" 2020-2022, which is financed by the Danish Environmental Protection Agency, we are analysing samples from the station at Sønderho-Ø (RIB1510007) for the species composition and abundans/biomass of phytoplankton, incl. NIS (non-native species) and HAB (harmful algal bloom-species). The data is e.g. used in connection with preparing the annual status report on marine areas published by DCE/Aarhus University.


Phytoplankton, including poisonous and harmful algae

We offer ad hoc consultancy to the Danish Ministry of the Environment (phytoplankton in general) and the Ministry of Food, Agriculture and Fisheries (poisonous algae) about the prevalence and occurrence of phytoplankton. This also includes the Wadden Sea. For example, we have advised the Danish Veterinary and Food Administration in relation to the prevalence of poisonous algae in the North Sea, including the part of the North Sea that covers the Wadden Sea. In addition, we participate in expeditions and other fieldwork when possible. Among other things, in the late summer we will be working with the Alfred Wegner Institute in Bremerhaven, where we will map the prevalence and occurrence of phytoplankton in the interplay between the Wadden Sea and the North Sea. A special focus of this study is molecular and microscopic taxonomic studies of algae with toxic effect.

Read more here (in Danish).


What affects the number of migratory birds in the different sub-areas of the Wadden Sea?

Monitoring has shown that the number of migratory waterfowl has declined significantly in the German part of the Wadden Sea, in contrast to the Danish and Dutch parts. The studies include an analysis of the sediment conditions in the three areas, including climatic conditions and other regional factors that may affect the macro-distribution of resting waterfowl.


Where do the birds of the Wadden Sea rest at high tide: Is the human activity a crucial factor?

The Wadden Sea is an important area for migratory waterfowl. When it is high tide, the birds save energy by resting near the wading surfaces where they forage for food at low tide. However, human activity can make the many thousands of waterfowl fly away. In some cases, the birds have to fly several kilometres before they find a new resting site. We illustrate the need to take a closer look at the conflicts that may exist between locations, where outdoor activities are practised in the Wadden Sea, and locations, where waterfowl prefer resting undisturbed during high tide.


Identification, dispersal routes and possible interventions for invasive species in the Wadden Sea

The rate at which non-native species are introduced to Danish waters has risen sharply in recent decades. Shipping is considered to be a significant dispersion vector via discharge of ballast water and hull fouling. The main purpose of this project, which concerns NIS species (non-indigenous species) in the Wadden Sea, is to help identify possible new initiatives against these species. We use conventional monitoring methods, eDNA methods and modelling of dispersal routes.


Long-term development in the breeding birds' populations in the Wadden Sea: Which factors are crucial?

From the Trilateral Wadden Sea Partnership, we know that many of the characteristic breeding birds of the Wadden Sea are in decline. For example, this applies to avocet, oystercatcher and common ringed plover. We use species-specific surveys and 50 years of registrations from Tøndermarksen and the island Langli as well as 25 years of registrations from other areas of the Wadden Sea to identify the factors that have determined the well-being of the populations. On this basis, we present recommendations for initiatives that will help to secure the populations against further decline.


The structure of porpoise populations in the Wadden Sea and the North Sea

Satellite tagging of porpoises in the Wadden Sea has shown that the animals here stay almost exclusively in the Wadden Sea area all year round. In contrast to this, the porpoises in the central North Sea move over great distances. Genetic analyses of the porpoises tagged in the Wadden Sea and in the North Sea as well as in the inner Danish waters have been initiated and will be able to reveal whether there is a separate population of porpoises in the Wadden Sea. This can have a major impact on how to protect the relatively small number of porpoises in the Wadden Sea in future.


People and nature in the Wadden Sea

The Wadden Sea area provides a geographical framework for a historical and sociopolitical Nexus, both in relation to the interplay between culture and nature, in relation to the tensions between different nature interests, and in relation to the conflicts between the central administrative nature management authorities and the local population.

Due to the very special nature conditions that prevail in the Wadden Sea and the tensions that have taken place in and around the Wadden Sea, the area has, more than any other nature area in Denmark, impacted not only Danish nature management, but also the political development in Denmark. The Wadden Sea therefore constitutes a central case, both in relation to the development of more adaptive and inclusive nature management, including the study of change processes,how people relate to nature, and in developing a more constructive interaction between citizens and authorities as well as in the study of various nature conflicts and conflicting interests.


Natural coastal dynamics and effects on biodiversity

We work with biodiversity and nature conservation in the terrestrial coastal ecosystems, coastal dunes, salt marshes and marshes. Concentrating on natural, dynamic processes in the coastal zone, such as sand drift, erosion, flooding and natural grazing, our research focuses on quantifying the effects on biodiversity. In addition, we have previously studied the consequences of the increasing sea level on the Danish salt marshes (coastal squeezing). In the Wadden Sea, the natural dynamics are particularly interesting – it is one of the few places in Denmark where the dunes can develop due to sand being transported down the West coast. At the same time, the tide is yet another natural disruption that affects the coasts of the Wadden Sea – especially the salt marshes, which are formed and erode faster in the Wadden Sea than elsewhere in the country. Climate change and the biodiversity crisis make our research on the conservation and restoration of the natural processes highly topical. 


Monitoring porpoises in the Wadden Sea

Porpoises are monitored once a year by aircraft in the Danish part of the Wadden Sea and in the adjacent large N2000 site the "Southern North Sea". The surveys began in 2011, and the number of porpoises is calculated for the entire area (the Danish Wadden Sea and the Southern North Sea). Data shows that the number of porpoises in the area varies from year to year, from approx. 1000 to 6,500 individuals. This is probably due to changes in prey distribution from year to year. In 2020, we counted 5,930 porpoises (95% confidence interval: 3,895 – 8,310 porpoises). Calves have been observed in the waters next to the Wadden Sea every year. The Inner Wadden Sea (the water east of Römø, Mandø and Fanø) is not particularly suitable for aerial surveys, as most of the Wadden Sea is too shallow for porpoises to swim in, apart from the deeper canals, which are not very well covered by straight transect lines. Tagging of wild porpoises in the Wadden Sea with satellite transmitters have shown that porpoises in the Wadden Sea are very stationary.


Monitoring seals in the Wadden Sea

The development in the populations of the harbour seal and grey seal in the Wadden Sea has been monitored by means of photos taken from planes since the 1970s. During the moulting period, a large and stable proportion of the population stays on land, and the counts are used to monitor the development in the size of the populations. All the pups are born on land, where they fed by their mothers for 3-4 weeks. At this time of the year, the pups are counted in order to estimate the year's pup production. Monitoring is carried out in collaboration with researchers in Germany and the Netherlands, so that the entire Wadden Sea area is covered in a coordinated manner.

The Trilateral Wadden Sea secretariat publishes annual reports on the development of the two seal species.

Sanitary survey

A sanitary survey is an assessment of the interactions between potential sources of pollution, climatic conditions, water movements, etc. in a demarcated area, such as the Wadden Sea. The reports address issues that are deemed to have an impact on potential microbiological contamination. This applies, for example, to oceanographic and climatic conditions, the prevalence of game animals, fishing and the use of the catchment areas and industries that have emissions to the area. Two reports have been published in the series concerning the Wadden Sea. They are updated every six years. Reports are in Danish.


Wadden Sea Model

The water movement in the Danish part of the Wadden Sea is simulated with the 3D hydrodynamic model FlexSem. An unstructured calculation system has been used with a maximum horizontal resolution of approx. 250 m in the tidal canals and a lower resolution of approx. 2.8 km on the open edge towards the North Sea. The model uses wet/dry so that areas can dry out at low water levels. The model years are 2019, 2020 and 2021. Outputs are water velocities, water levels, temperature, salinity, etc. in high resolution in time and space. For instance, the model can be used to calculate pathways of dispersal of invasive species via ports, shipping routes, wind farms and adjacent areas.



Wadden animals and plants: The role of key species in the Wadden Sea ecosystem

The Wadden animal and plant life is of crucial importance its many consumers, such as birds, fish, crabs and shrimp, who use the Wadden Sea as a pantry. Among the species of the Wadden Sea, some are particularly important because of their role as habitat formers (e.g. eel grass, sandworm, crayfish, cockles). The theme of this research area is to uncover the distribution patterns and the dynamics of the key species of the sandy bottom in relation to abiotic and biotic conditions in order to understand their interactions with other species, including their significance for consumers and the ecosystem as a whole.


Virtual fencing on Fanø

On the east side of Fanø, we have permission to conduct an animal experiment where a herd of Angus cattle will be fenced using a collar with sound, which signals where the boundary, i.e. the invisible fence, is. When the cow approaches the limit, a sound is emitted. The sound is amplified until the limit is reached. If the cow crosses the boundary, it receives an electrical impulse. The collar has a built-in GPS transmitter and is powered by solar cells. The animals have been good at adapting to the system, which has great potential in both nature parks and in the National Park Wadden Sea, where establishing fencing is not always easy. The study is controlled by professionals, as it is conducted as an animal experiment.

The virtual fencing experiment was achieved through a collaboration between farmer Michael Baun, initiator Dan Pode Poulsen, Fanø Municipality and the National Park Wadden Sea, who also constitute the steering committee along with a representative from HedeDanmark. The study is supported by: The June Foundation, Markus Jebsens Naturpulje and Hedeselskabet.

Breeding birds on the beaches in the Wadden Sea: How do we protect species from foxes, beach tourism and extreme summer high tides?

Römø and Fanø constitute the most important breeding areas in Denmark for the Kentish plover and the little tern. Since foxes were introduced to the islands, especially the terns have tried to avoid the foxes by moving far out on the beaches. But here, eggs and chicks can easily disappear during extreme summer high tides. We examine the extent to which breeding birds lose eggs and chicks as a result of foxes, high tide and human disturbances. In addition, we are collaborating with the National Park Wadden Sea and the Danish Nature Agency to find ways to protect birds' eggs and chicks against foxes, floods and beach tourism.