In our working group "Ecosystem Analysis" we investigate how the food webs of our coastal ecosystems change and develop due to natural and human-induced influences. To do this, we use data from a wide variety of fields to combine them into food web models and find out how the ecosystem as a whole is evolving.
Our coastal waters are highly productive systems, with multiple food interactions between different organisms. While the term "food chain" was often used in the past, we now know that trophic relationships are much more complex and that the plants and animals in our coastal waters are interdependent in a diverse network - the food web.
Plankton and organic material form the basis of this network. From there, the energy provided is passed on to the higher trophic levels, such as fish, birds and marine mammals, via a large diversity of benthic organisms. Thus, in the coastal food web, each organism plays an important role in enabling the ecosystem to function. Natural, but more importantly, man-made impacts affect individual species, communities, and habitats. The resulting changes are transmitted directly and indirectly through the food web, so an initially small impact can have large effects on the entire ecosystem. Food web models help us to better understand these impacts and to better understand the structure and function of an ecosystem.
Anthropogenic uses in the North Sea: Impacts on marine top predators
Human activities have various, mostly negative, impacts on marine top predators; steadily growing intensities of use are increasing pressures on marine species and habitats. Currently, the expansion of offshore wind energy use in the German EEZ is progressing rapidly; plans for the next decades indicate large-scale dimensions. At the same time, species and ecosystems are exposed to other forms of use. For example, numerous fish stocks have been severely depleted by intensive fishing. Noise input from construction activities, shipping and blasting can also have a demonstrably negative impact on species.
Overall, German marine waters are already in a poor state of conservation (MSFD). It is unclear when the ecosystem stress limit will be reached. Thus, understanding the cumulative effects of anthropogenic uses and estimates of the consequences of further expansions of uses is crucial. In AnthroTop, we are using models to predict how different use scenarios in the North Sea might affect the distribution of marine top predators and what this might mean for marine ecosystems, particularly food chains.
Scientific studies on the biology and fisheries of the North Sea shrimp CRANgon crangon as the basis for an efficient self-MANagement system
Catch of the brown shrimp Crangon crangon (Photo: Merten Saathoff, Alfred-Wegener-Institut)
In the project CRANMAN II, we are dedicated to the task of further developing the scientific basis for fisheries management of the brown shrimp Crangon crangon. The brown shrimp stock is not subject to international management at EU level and there is no operational management at national level, either through quotas or effort restrictions. As part of the sustainability certification by the Marine Stewardship Council (MSC), the fishery has committed itself to self-management based on scientific findings.
Therefore, in CRANMAN II we are analysing the development of stock indicators of the brown shrimp in different regions. These include growth and mortality rates, but also the influence of fluctuating recruitment on the overall stock. This includes environmental factors as well as drift and migration processes. Furthermore, the role of the brown shrimp in the food web is studied in more detail.
Environmental changes directly and indirectly influence the structure and function of marine ecosystems in complex ways. Due to the high degree of interconnectedness of marine ecosystems in ecological, economic as well as social interests, system changes also propagate outside the actual ecologically defined boundaries. The result is a combination of internal and external interactions and intercorrelations on multiple scales. Understanding the influence of environmental changes on structural properties of this combination of interactions lays the foundation for successful ecosystem-based management in the face of future challenges.
Models, as simplifications of observable phenomena in nature, can provide specific insights into individual components of an ecosystem or, more holistic, into entire interaction networks. A well-known approach to investigate such interaction networks of feeding relationships, so-called food webs, is network modeling followed by the Ecological Network Analysis (ENA). This approach provides not only a structural understanding of network properties, but also specific functional indices that create a quantitative basis for ecosystem management decisions. However, this modeling method is static in space and time and the results can be interpreted as snap-shots of the system rather than a continuous development. Consequently, an investigation of continuously resolved influences of environmental changes on food webs and its responses on the ecosystem is not possible.
The DEcolog project aims to be a prelude towards a holistic and dynamic ecosystem model. The coupling of a dynamic ocean model with a static network model including ENA will combine the capabilities of both approaches to resolve and trace the influence of abiotic shifts. Therefore, a temporally as well as spatially resolved ENA becomes possible, which can quantitatively analyze dynamic shifts in the abiotic environment and allows an assessment of possible subsequent management interventions.
As part of the long-term ecological series, a high-resolution monitoring of fish stocks in the German part of the Sylt-Rømø Bight was started in 2006. At 7 stations along the Lister Ley and the Pander Deep, changes in the fish fauna are recorded. Since 2019, a station in the Danish waters of the bay is also approached.
For the monitoring, a mini-round trawl is used from the research vessel Mya II, which has a length of 17m and an opening width of 7m and an opening height of 3m. The mesh size is 32mm in the wings, 16mm in the midsection and 6mm in the codend. This net can be used directly on the bottom or on a short line as a so-called flyde trawl in the water column. Due to the high dynamics of the fish community in the Wadden Sea, we have to carry out the stock checks monthly, additionally one sampling site each in the estuary of the Lister Ley and one in the inner bay are examined quarterly. The collected fish are identified on board, counted and their total length determined. Over the years, we will be able to make statements about climate-related or anthropogenic changes, such as the direct and indirect influence of fishing in the Wadden Sea on the use of the Wadden Sea by fish, and thus to specify their role for biodiversity and for the food web.
Marine Biodiversity and Ecosystem Functioning leading to Ecosystem Services
The overall objective of MARBEFES is to identify the links between biodiversity, the function of different ecosystems and the resulting ecosystem services. Based on this, an ecological and socio-economic assessment of the systems will be made using new approaches to improve policy and management of the marine environment and ensure its benefits for present and future generations. We will go substantially beyond the current state-of-the-art science in understanding the causes and consequences of biodiversity decline, the loss and gain of ecological and economic value, and the implications for marine management and governance in European seas.
Exclusion of mobile bottom-contact fisheries in Marine protected Areas of the German EEZ of the North Sea
Bottom trawl (Photo: Hermann Neumann, Thünen Institut)
Marine conservation measures within designated protected areas of the German exclusive economic zone (EEZ) represent a key management approach to counteract the steady decline of fish stocks, the destruction of marine habitats and the loss of biodiversity. Since 2023, the use of mobile bottom-contact fisheries (mobile, grundberührende Fischerei = MGF) has been excluded in large parts of the German Marine Protected Areas in the North Sea. In our project MGF-Nordsee, we investigate how this exclusion affects the ecosystems of the protected areas. In the last years, we have already recorded a comprehensive baseline status of the areas. Now we are tracking what initial effects can be observed as a result of the exclusion.
