Junior research group
Microorganisms are found everywhere in the oceans but in coastal regions the interaction of humans and marine microorganisms is most intense. Research priorities of our group include microbial ecology and interactions in coral reef ecosystems, microbial management in aquaculture systems, and the proliferation of pathogenic bacteria. Microbial interactions relevant in biogeochemical cycles, such as vertical fluxes of organic carbon in shallow coastal to open ocean systems are an overarching research focus of our group.
Free-living and particle-attached microbiology
Particles, such as marine aggregates, are heavily colonized by prokaryotic microbes, as they contain high amounts of (labile) organic matter and nutrients. Further offshore, marine aggregates represent an important part of the biological pump whose efficiency also depends on the particle attached microbial activity (i.e. respiration, remineralization of organic matter).
In shallow coastal regions, sinking aggregates do not only determine the sedimentation rates of organic matter to the underlying sediments. Depending on current strength, they can act as vectors, transporting materials from A to B. As these materials may also include pathogenic bacteria, toxic chemicals or simply high amounts of organic matter, our group aims at understanding the role of aggregates as vectors in coastal tropical ecosystems.
Rolling tank experiments to study marine particles and their associated microbial communities at a high resolution.
Coral reef microbiology
Tropical coral reef ecosystems often support enormous biological diversity, including structurally and functionally complex benthic communities, and provide key ecosystem processes. As a result numerous delicate interactions may arise among species and their surrounding environments, making these ecosystems particularly susceptible to changes in environmental parameters. Coastal development, intensive farming in the hinterland and fish farm aquaculture are major sources of eutrophication in tropical coastal areas, potentially leading to the disappearance of coral reefs, mangroves and seagrass meadows.
Microbial processes largely control the health and resilience of coral reef ecosystems and microbial communities are thought to be an important component of the corals' ability to adapt to environmental change. Reef building corals live symbiotically with algae, protists, bacteria and viruses in spatially distinct patters to function as holobionts. Slight changes in microbial community structure due to environmental changes can have a great impact on the reef ecosystems. Thus, understanding the ecological impact of different sources of eutrophication on microbial associations in coral reefs can provide a scientific basis for tropical costal management.
Strategies of opportunistic pathogenic bacteria to infect a coral host in a eutrophied reef.
Microbiology of aquacultures
Because of the dramatic decline of natural fish stocks, aquacultures are becoming increasingly important. Ecological threats, such as eutrophication and biodiversity loss, as well as health concerns (e.g. the occurrence of pathogenic microorganisms) lead to current concerns about coastal aquaculture practices. Intense tropical aquaculture practices may lead to anoxic conditions in the water column, the warm temperatures are ideal for the rapid growth of bacteria, including pathogens, and a high organic matter load (resulting from aquaculture wastes) provide an easily degradable food source supporting the proliferation of heterogenic bacteria.
Currently, projects based in Indonesia, Philippines, and Vietnam investigate the abundance, diversity, community structure and function of prokaryotic microbes within and close to aquaculture impacted sites. Furthermore, screening for the occurrence of pathogenic bacteria in shrimp and fish aquacultures are conducted, microsensor measurements of oxygen and hydrogen sulfide are carried out, and water quality parameters are monitored.
Given the importance of aquaculture for the local population and the need for sustainable practices, such research projects are conducted in close collaboration with local scientists and often include mutual visits to foster a productive knowledge exchange.
Sample collection at a seaweed farm in Vietnam.
Milkfish aquaculture in Bolinao, Philippines.
Gammaproteobacteria, including the Vibrio species, generally thrive well in warm and estuarine waters with high amounts of organic matter load. Especially in tropical regions the occurrence of Vibrio cholerae is of high concern for human health. V. cholerae is a gram negative, facultative anaerobic bacterium and some pathogenic strains can cause the disease cholera. Eutrophication and climate change in tropical coastal waters may lead to favourable conditions for the growth of pathogenic bacteria such as V. cholerae. Therefore, together with monitoring environmental conditions of tropical coastal waters, we screen for potentially pathogenic microbes and the presence/absence of pathogenic genes using qPCR.
Sewage outflow in a polluted estuary in Bangladesh, where a high abundance of V. cholerae has been detected.