Human activities in the North Sea
Human activities in the ocean often interact and overlap in space and time. As a result, their impact on the ecosystem can be synergistic, where their combined effect is greater than the sum of their individual effects. As part of the MGF-Nordsee project, we investigated the occurrence of six different human activities inside and outside the German EEZ Natura 2000 sites using EMODnet open source data. We found that a large proportion of the activities still take place inside the MPAs, with an even higher proportion of cables and pipelines inside the MPAs than outside.
The role of macrofauna in sediment reworking
Benthic macrofauna plays a central role in sediment reworking, important for organic matter distribution and carbon sequestration. A reduction in their activity can have consequences for ecosystem functioning. We conducted an experiment measuring the bioturbation rates of two contracting functional types of benthic macrofauna under different organism densities and nutrient enrichment conditions. With a luminophore tracer method, using fluorescent sand particles, we tracked the sediment reworking behaviour of the organisms. Analysing the sediment profile images showed that a reduction in organisms increased the bioturbation rates, yet material was buried significantly shallower compared to natural densities.
Spatial variation in sediment microbiota
We use DNA sequencing to characterize microbial communities from the North Sea and utilize spatial models to understand how microbiota vary taxonomically and functionally throughout space and time. For this, we have established a monitoring program to collect samples across the German North Sea. Since 2019 over 350 stations were repeatedly sampled. This large dataset is preserved and maintained at the ICBM and will grow over the coming years.
Preliminary results suggest that sediment microbiota vary in response to sediment characteristics, temperature and organic content but also to bottom trawling activity and natural bottom disturbance.
Endofauna and epifauna surveys in the Natura 2000 sites
The endofauna includes all animals that live in the sediemtns of the seafloor. A total of 85 stations at the Dogger Bank, the Sylt Outer Reef and the Borkum Reef ground were sampled for their investigation. The statistical data analysis shows that each area has its own endofauna community. In addition, first results indicate that there are significant correlations between the species diversity of the endofauna and the fishing intensity, but also the sediment structure, at the Dogger Bank and in the Sylt Outer Reef.
In parallel, the epifauna in the Natura 2000 areas was sampled. The epifauna includes those animals that live on the seafloor. The study revealed that the species diversity of the epifauna differs in the three areas, influenced by the different environmental parameters. Results of a long-term epifauna data analysis from Dogger Bank over the last three decades further showed that the epifaunal communities were primarily influenced by fishing intensity in the 1990s, while since 2003 they have been increasingly altered by the climatically induced increase in water temperature by 4 °C (>25 m water depth).
Investigation of the North Sea with video stations
The benthic fish and invertebrate communities were studied in two marine protected areas of the German North Sea using baited underwater video stations (BRUVs). In contrast to the traditional biodiversity monitoring using trawling, BRUVs are a low-impact method to describe species communities. In addition, the comparison of the two methods shows that they record different species, but also overlap. Therefore, a complementary combination of both methods provides the most comprehensive results on the status of marine protected areas. After the exclusion of bottom-contact fisheries, an adapted, non-invasive monitoring plan can be developed based on these studies.
Large stones are rare in the North Sea, but form stone reefs in some places. These provide a special habitat for sessile organisms such as soft corals and sea anemones. Since conventional survey methods are unsuitable for these reefs, video transects were recorded by research divers. The recordings allow an investigation of the species that are present and how they are influenced by factors such as fishing, depth, current and sediment composition.
Trawl marks on the the seafloor
We use hydroacoustic methods (e.g. sonar) to investigate the influence of bottom-contact fisheries on the seabed, and the sediment composition and structure. The backscatter strength of the acoustic signal provides information about the condition of the seabed. This allows us to identify where trawls have been dragged across the seabed. Initial results from the project show that the detectable structures on the seabed disappear after only a few months. The sediments seem to level out again relatively quickly, moved by ocean currents.
Autonomous Reef Monitoring Structures
One Method to analyze benthic communities are Autonomous Reef Monitoring Structures (ARMS). These standardized 3D structures mimic the complex structure of sea bottom habitats (e.g. reefs). The stacked PVC plates offer an attachment substrate for larvae, incrusting invertebrates and hiding spaces for small animals. We deploy the ARMS while diving and attach them with steel rods to the seafloor next to reef structures to evaluate the response of cryptic, often overlooked reef communities to the different management practices (e.g differences in fishing pressure). In 2021, we deployed 49 ARMS at 10 different stations at the Sylt Outer Reef and Borkum Reef Ground. We will fetch the first ARMS in June 2022 from the seabed and investigate which organisms settled on the individual PVC plates.
Baited Remote Underwater Videostations
The development and test of new non-invasive sampling methods is an important part of MGF-Nordsee. The use of baited remote underwater videostations (BRUV) provides unique insights into the underwater world of the North Sea.
In the first year of the project, many interesting recordings have already been captured in the Natura 2000 areas, which help to determine the biodiversity in the areas.