Researchers at the Max Planck Institute for Chemistry in Mainz used nitrogen isotope analysis of 2 extinct groups of coral fossils, tabulate and Rugos.
They found that the symbiotic relationship between Coral and Algae existed over 385 million years ago, in the Devonian period.
During the Middle Devonian period, the Eifel and Sauerland regions in Germany were covered with tropical seas.
The fossilized corals of the extinct orders Tabulata and Rugosa found in this region confirmed their presence during this period. However, it was still unclear whether a distinct group of corals performed photosynthesis or not.
The researchers demonstrated the symbiotic relationship by comparing the nitrogen isotopes of today’s symbiotic and non-symbiotic corals. The ratio of “heavy” nitrogen (15N) to “light” nitrogen (14N) can effectively be used to differentiate the stages of the food pyramid.
For instance, analyzing nitrogen isotopes can determine whether the creature had a vegetarian or meat-based diet. If the nitrogen isotope value is high, the organism is ranked higher in the food pyramid.
Moreover, different lines of evidence have suggested that the nitrogen isotope value of organic matter bound to the calcifying organisms remains unaltered for millions of years. Therefore, the coral-bound organic matter can be used to assess photosymbiotic activity in fossil corals.
“The constant difference in nitrogen isotope values is in line with our expectations and shows the typical jump in the food chain. This is because symbiotic corals are one level below non-symbiotic corals in this hierarchy,” says Jonathan Jung.
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To determine the symbiosis, researchers analyzed the fossils collected from the Sauerland region. The specimens of Tabulata and Rugosa showed significantly lower nitrogen isotope values, which led researchers to conclude that they already lived in photosymbiosis during the Middle Devonian period.
“Photosymbiosis could explain why ancient reefs were highly productive and enormous in size despite the nutrient-poor environment,” says Alfredo MartÃnez-GarcÃa.
“Moreover, this new insight allows for a better understanding of the food chains of early reefs,” adds Eberhard Schindler.
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Corals, despite being very sensitive to temperature and nutrients, this study could offer better insights into ancient coral reefs that grew in oligotrophic (low-nutrient) environments. Moreover, this investigation could open up inquiries into the nutrient cycle of the Paleozoic era.
Journal Reference
- Jung, J., Zoppe, S. F., Söte, T., Moretti, S., Duprey, N. N., Foreman, A. D., Wald, T., Vonhof, H., Haug, G. H., Sigman, D. M., Mulch, A., Schindler, E., & Janussen, D. (2024). Coral photosymbiosis on Mid-Devonian reefs. Nature, 1-7. DOI: 10.1038/s41586-024-08101-9
