Supervisors:

PI: Peter Schupp Co-PIs: Gabriele Gerlach, Thorsten Brinkhoff, Thorsten Dittmar

Research and projects:

Rising sea surface temperatures caused by the ongoing global warming are affecting a large number of marine ecosystems. According to many climate models, tropical coral reefs are expected to suffer severely under the increasing sea surface temperatures. In order to adapt to a changing environment many organisms rely on recruitment. Juvenile organisms often exhibit a larger physiological plasticity allowing them to develop in conditions that are insufficient or even detrimental for the parental generation. Microorganisms such as certain strains of substrate-bound bacteria play a significant role in the distribution of juvenile marine invertebrates by releasing compounds that induce settlement and metamorphosis in pelagic larvae. A large number of coral species rely on the presence of certain bacteria in order to find a suitable place to attach to. However, many of the underlying mechanisms as well as the bacteria themselves and their chemical compounds are still unknown.

Subsequent to the settlement, the majority of scleractinians need to acquire symbiotic dinoflagellates of the genus Symbiodinium. These single-celled algae, also known as zooxanthellae, are contributing significantly to the corals’ energy yield by providing metabolites from their photosynthesis. There is a large variety of zooxanthellae associated with corals. Taxonomically organized in clades, thermal tolerance of the strains can vary significantly and strains of different thermal tolerance can be found within the same species correlating with the conditions of the respective habitat. However, under shifting conditions the adult colonies are not able to integrate new symbionts into the symbiosis that might be able to sustain the life of the colony. Under prolonged thermal stress this leads to the loss of the majority of hosted symbionts. This phenomenon is commonly known as coral bleaching. If conditions don’t normalize within a certain period of time the affected coral colony dies. It is assumed that the symbiosis is developing within the first months after settlement. The initial symbiont diversity in the polyps is often relatively high. 

After a few months, algal symbionts are reduced to one or two different strains. This symbiosis is then consolidating and the selection of the symbiont strains is assumed to be irreversible. However, it is not known in which way elevated temperatures might influence the process of symbiont selection. It cannot be ruled out that scleractinians might be more adaptive towards elevated temperatures than commonly assumed. 

This study will examine the microbial communities of potential settlement substrate and the process of settlement and metamorphosis of multiple coral species. Subsequently the uptake and selection of endosymbionts will be investigated by conducting adequate laboratory experiments and molecular analysis. The collected data will reveal a detailed insight into the first life stages of scleractinians as well as the development of symbioses and the adaptive potential of scleractinians.