Research
Research
Coral research
Coral reefs are declining worldwide, mainly due to anthropogenic influences. Sexual reproduction is essential for the recolonisation and recovery of damaged reefs. However, the early life stages are often neglected by scientists. Our research focuses on the effects of stress factors such as elevated temperatures and sedimentation on young corals. We conduct long-term experiments with juvenile corals to assess their adaptability. To better understand the settlement of coral larvae, we investigate chemical signals that induce the settlement and metamorphosis of coral larvae. Another focus is on the development of methods for the mass production of juvenile corals from gametes. The sexual reproduction of corals has the potential to produce large quantities of juvenile corals for reef restoration and the aquarium trade.
Chemical ecology of invasive species
Biotic invaders are species that establish a new area in which they proliferate, spread and persist to the detriment of the environment. The geographic scale, frequency and number of introduced species increased over the last years due to the expanding transport and commerce. Especially invasive algae are of global concerns since over 400 introductions have been reported worldwide.
The new German deepwater port, Jade-Weser port, in Wilhelmshaven, offers a good opportunity to study impacts of potentially invasive species. The enhanced shipping traffic in the Jade-Weser-Port range may result in the arrival of a variety of exotic species entrained with the ballast water or as fouling species attached to the vessel's hulk. Identifying future invaders and taking effective steps to prevent their dispersal and establishment constitutes an enormous challenge to both conservation and international commerce. To ensure a targeted monitoring in the North Sea, potentially invasive species were determined for the Jade-Weser-Port range in collaboration with Prof. Dr Bernd Blasius and his team. A model was developed, which focused on possible invaders through ballast water exchange of large vessels. Possible invaders were ranked regarding their invasive history and geography, resulting in macroalgae species, which could spread in the Jade-Weser Port range. The chemical defence abilities of these potentially invasive species are being compared with non-invasive related species in variable bioassays, which include but are not limited to antifouling, antisettling and antifeeding activities. The aim is the identification of special invasive traits and chemical compounds, which are advantageous for their invasive success.
Marine natural products research
Besides our investigations on the ecological role of marine secondary metabolites we are looking at their pharmacological potential as new drug candidates. Target organisms include invertebrates such as sponges and ascidians from shallow and deep-water environments ranging from 10 to 400 feet. Besides the macroorganisms we also screen bacterial isolates from these holobionts for various biological activities. Screens are conducted in collaboration with groups in Germany, England and the USA and include various antimicrobial, anticancer and antiinfectant assays. Active extracts are followed up with state of the art isolation techniques to identify the active compounds.
Ecotoxicology
The projects investigate the effects of pesticides, herbicides, antifouling paints and other anthropogenic chemicals (e.g. PCBs) on the fitness of various organisms. We are also evaluating the potential of various marine invertebrates (soft corals) as biomonitoring organisms for tropical regions.
Detailed information on our projects can be found under the headings Ecotoxicology of corals and Pollutant monitoring of seabirds.
Microbial symbiosis
Many marine sponges harbour dense and diverse microbial communities that are both ecologically and biotechnologically important. These microorganisms, which can account for up to 35 % of the total volume of a sponge, can be categorised as eukaryotes, archaea and bacteria, and at least some of these microbes appear to be largely specific to their sponge hosts. Recent high-throughput sequencing studies of sponge-associated microbial communities from different geographic regions and habitats have expanded our knowledge of the microbial composition of low and high microbial abundance sponges, categorising their communities as 'core', 'variable' and 'species-specific'. To achieve such a degree of host specialisation, three different transmission scenarios for sponge-specific microorganisms are considered: (1) horizontal transmission, (2) vertical transmission and (3) a combination of both transmission routes.
Sponge-microbe associations are known to be a source of bioactive metabolites, with more than 290 new compounds being isolated from sponges every year. As at least some of these metabolites are thought to be produced by symbiotic microbes, the cultivation of sponge-associated bacteria is an important focus in the search for new marine natural products. However, most bacteria from environmental samples, including sponges, cannot be cultivated on artificial culture media. A promising approach to isolate so-called non-culturable microorganisms is the diffusion chamber method. Although there are different variants of this approach, the unifying feature is the attempt to cultivate bacteria in situ by allowing them to interact with other microorganisms and chemical components in the environment.
This was the first attempt to use diffusion chambers to isolate unculturable bacteria from sponges. The study was conducted by implanting diffusion growth chambers (DGC) into the tissue of Rhabdastrella globostellata reef sponges. We also investigate whether abiotic conditions influence the intraspecific microbial communities of sponges. It is hypothesised that sponges may serve as microbial refugia to compensate for disturbances as part of ecosystem resilience.
