How environmental conditions influence microalgae and coral communities

An international research team led by marine biologist Prof. Dr. Maren Ziegler from Justus Liebig University Giessen (JU) has developed an innovative method to reconstruct the past of corals and their symbiosis with algae by drilling coral skeletons. The results, published in Biology of global changeprovide new insights into changes in symbiotic unicellular algal species that are essential for the survival of coral reefs.

Symbiodiniaceae and coral reefs

Coral reefs are among the most species-rich and ecologically important ecosystems in the world. Their health depends on the symbiosis between stony corals and species of unicellular algae called Symbiodiniaceae. This symbiosis enables the calcification processes that build the structure of the reef. However, this symbiosis is also sensitive to thermal stress, which can lead to coral bleaching. In this phenomenon, the coral loses its symbionts, jeopardizing its food supply and growth.

New method to reconstruct historical communities of Symbiodiniaceae

Researchers used drill cores from coral skeletons in Palau and Papua New Guinea to reconstruct the dynamics of Symbiodiniaceae communities over the past 110 years. “Our method allows us to analyze Symbiodiniaceae communities in coral skeletons, thus providing unique information on the history of this symbiotic partnership,” explains Professor Ziegler, leader of the study. The drill cores were collected during the international Tara Pacific expedition to the coral reefs of the Pacific and subsequently analyzed.

The study shows that reconstructed Symbiodiniaceae communities vary considerably between species and locations. Particularly striking are the dynamics of samples from Palau, where historical heat stress events are associated with changes in algal communities. “Our results suggest that coral skeletal reconstructions not only provide clues about past environmental conditions, but can also reveal how Symbiodiniaceae adapt over time,” explains Professor Ziegler.

Significance for future research

The new method opens up many possibilities for studying the history and dynamics of coral reefs, similar to terrestrial tree rings. “By combining the data, we can see clear correlations between changes in Symbiodiniaceae and past environmental conditions,” explains the researcher. This information can improve predictions about the condition and health of coral reefs, for example under conditions of climate change.