How coral reefs can survive climate change

Similar to expeditions a hundred or two hundred years ago, the Tara Pacific Expedition lasted more than two years. The objective: to research the conditions for the life and survival of corals. The ship traversed the entire Pacific Ocean, assembling the largest genetic inventory conducted in any marine system to date.

Image credit: University of Konstanz

​​​​​​​The team of 70 scientists from eight countries took around 58,000 samples from the hundreds of coral reefs studied. The first results of the analysis have now been published in Nature Communications. This largest collection of data on coral reef ecosystems is freely available and, for years to come, will be the basis for clarifying the living conditions of corals and finding a way to survive climate change.

Important first findings of the expedition: global microbial biodiversity is much higher than previously thought. The impacts of the environment on evolutionary adaptation are species-specific. And important genes in corals are duplicated.

Global biodiversity ten times higher than assumed

Coral reefs are the most biologically diverse marine ecosystem on Earth. Although they cover only 0.16% of the world’s oceans, they are home to about 35% of known marine species. Using a dataset based on genetic markers, the researchers found that all of the globally estimated bacterial biodiversity is already contained in the microorganisms of coral reefs. “We have completely underestimated global microbial biodiversity”, says Christian Voolstra, professor of adaptation genetics in aquatic systems at the University of Konstanz and scientific coordinator of the Tara Pacific expedition. He says the current biodiversity estimate (about five million bacteria) is underestimated by about a factor of 10.

The impacts of the environment on evolutionary adaptation are species-specific

The 32 archipelagos studied serve as natural laboratories and provide a wide range of environmental conditions, allowing relationships between environmental and genetic parameters to be untangled on large spatial scales. This led to another important discovery: the effects that the environment has on the evolutionary adaptation trajectories of corals are species-specific. To determine this, the researchers first examined telomeres, the ends of chromosomes that carry genetic information.

In humans, telomere length decreases during life, ie with an increasing number of cell divisions, suggesting that biological age is closely related to telomere length. Researchers from the Tara Pacific expedition have now discovered that the telomeres in highly stress-resistant corals are always the same length. “They apparently have a mechanism to preserve the length of their telomeres,” concludes Volstra. In a more stress-sensitive coral species, which also has a shorter life span of about a hundred years, telomere length is aligned with environmental stresses, such as temperature fluctuations. “A direct imprint of environmental stress levels on organismal resilience may also have implications for human health”Voolstra says.

Important genes are duplicated

Research data from the Tara Pacific expedition have revealed that the long life of some coral species may have another reason: the duplication of some genes. Many important genes are present multiple times in the genome. The researchers were able to determine this by sequencing coral genomes using a new high-resolution technique. This technique called long-read sequencing allows not only to determine the set of genes present, but also to observe their order in the genome. According to Voolstra, the pervasive presence of gene duplication could be a possible explanation for why corals can live for thousands of years despite being exposed to, for example, extreme UV radiation in shallow water.

The Tara Pacific Expedition, named after the research vessel, will provide material for large-scale analyzes of coral reef ecosystem diversity for years to come. What is also unique about the program is that the samples were collected from multiple locations and over several years. The researchers examined the corals at each site identically, which makes the results entirely comparable.

The entire data collection is freely accessible

All datasets are openly accessible and fully described with accompanying physical and chemical measurements to provide them as a scientific resource for all researchers. “This is unique”, says Volstra. “It is the largest collection of coral reef datasets ever collected and is completely open access.” The aspiration is that this collection of data will serve as a foundation and inventory to guide future study of coral reefs around the world for many years to come.


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