Research 

The overarching theme of the workgroup is chemical ecology of marine organisms. We have been using chemical techniques to evaluate the role of marine natural products in their environment, while at the time also looking at potential pharmacological activities in selected compounds. Much of the work is focused on tropical coral reefs where chemo-ecological interactions among epibenthic organism are especially common to persist in this competitive environment. 

Sexual reproduction in scleractinian corals

Coral reefs are biodiversity hotspots which have become increasingly threatened by a multitude of anthropogenic stressors such as overfishing, pollution, but foremost climate change and the associated increase in sea surface temperatures1. Prolonged higher water temperatures disrupt the coral dinoflagellate symbiosis resulting in bleaching and eventually coral mortality², which can reach global scales as seen in the 4th global mass bleaching event in 2023-24³. The survival of coral reefs largely depends on the recruitment of a new generation of coral individuals that are more adapted to a rapidly changing climate and other anthropogenic stressors (e.g., pollution, sedimentation). Therefore, a better understanding of the coral settlement process, the molecules involved as well as crucial environmental drivers that control settlement success are needed. In recent years we made some major progress by isolating crustose coralline alga associated bacteria which produce the settlement cue cycloprodigiosin (CYPRO). The compound induces settlement in coral larvae4^,5 and the transformation of the recruit to a healthy juvenile polyp⁶. We have shown that CYPRO induces settlement in several Pacific broadcast spawning and brooding corals indicating that it might be a general cue and as such might have great potential in coral restoration research and projects. 

Ecotoxicological studies of birds and corals

Our group has been assessing the effects of various pollutants on birds for the last 15 years continuing a time series of 20 years. Bird eggs are collected along the Wadden Sea coast in the North Sea and analyzed for heavy metals, persistent industrial- and agro-chemicals.

Another project is focused on the development of a reliable test methods for assessing short- and long-term toxicity of chemicals against coral larvae and adult corals. This project is an industry collaboration to establish standardized ecotoxicological methods to test environmental samples, pollutants, and personal care products such as UV- filters for potential detrimental effects on coral larvae and adult hard coral. Since coral reefs are declining at a global scale due to climate change, stressor at local scales have also received increasing attention, including Ultraviolet (UV) filters used in sunscreens. This has already led to bans on various organic UV filters in some regions, although the underlying studies for these bans demonstrated significant flaws in the experimental design⁷. Our research aims to implement sound chemical analyses with targeted ecological assessment of coral health to provide recommendations according to international guidelines to environmental and government agencies. Once established such tests could provide safe development and use of agrochemical and personal care products.

Development of noninvasive monitoring methods to assess temperate and tropical marine ecosystems 

In a recent project on Mafia Island, Tanzania, we aim to address the decline of coral reefs and biodiversity by leveraging scalable and less labor-intensive monitoring techniques for sustainable coral reef and marine protected area management. The project seeks to promote a participatory approach in reef restoration efforts, involving community members in the restoration process. To effectively monitor and guide these community-based reef restoration attempts, the study will employ a combination of cutting-edge monitoring methods. These techniques include videogrammetry, Baited Remote Underwater Video systems (BRUVs), line and belt transects, and traditional taxonomic studies. Videogrammetry and BRUVs have already been successfully implemented to monitor MPAs and control sites in the North Sea.  Additionally, the project will validate data generated from environmental DNA (eDNA) analysis, a novel and promising approach for assessing biodiversity in marine ecosystems. By integrating multiple methodologies, we aim to establish the accuracy and reliability of eDNA in measuring biodiversity and monitoring changes in marine ecoysystems. If successful, such an approach could be used as a template in temperate and tropical monitoring programs. 

Understanding compositional and functional changes in benthic communities

Increasing anthropogenic stressors, foremost climate change, will likely result in many benthic communities undergoing compositional and functional changes. On coral reefs various benthic changes have been observed, including towards non‑hard coral‑dominated communities. The decline of reef‑building species and the increase of alternative (i.e., non‑reef‑building) organisms profoundly affect the functioning of coral reefs and the services provided, but this remains poorly understood, especially for non‑algal alternative communities⁸. Current research and monitoring around Manado Indonesia have already identified sites where parts of the reefs have shifted to soft coral or ascidian dominated communities. Our aim is the identification of drivers and triggers (e.g. potential environmental factors), feedback mechanisms, changes in ecosystem functions and effects on ecosystem services. Experiments in the aquarium facility evaluate the role of allelopathic secondary metabolites of sponges and how this could affect their competitiveness towards hard corals. Aquarium experiments are often matched with field experiments to validate results in situ.

Benthic community changes have also been studied in field and mesocosm experiments for the Wadden Sea. Using mesocosm experiments effects of nutrient enrichment and spatial nutrient heterogeneity on microphytobenthos and the cascading effects and interactions with macrofaunal consumers on tidal flats are evaluated.

Microbial ecology

Our current microbiological research is focused on sediment microbial communities of the North Sea and aims to disentangle how environmental, biological, and anthropogenic processes shape benthic microbiota and microbial processes. Our findings provide first insights into benthic microbial biogeographic patterns on a large spatial scale and illustrate how anthropogenic activity such as bottom trawling can alter the distribution and abundances of microbes and potential metabolism at the ecosystem scale.⁹ In the German North Sea, marine protected Areas (MPAs) were recently instated where fishing is partially or completely banned. This research project also monitors and studies the changes in benthic microbiota occurring within the MPAs. To this end, we established a bio-archive of sediment samples covering the German Bight, linked with a large microbial community dataset.

Bioprospecting of marine bacteria and invertebrates

We have established a large culture collection of marine bacteria and invertebrates of shallow and deep-water environments from various places. Organisms were mostly collected following ecological observation in the field often indicating superior competitiveness against other organisms. Often the production of bioactive compounds has been the reason why these organisms were so successful in their specific habitats.