Coral: A Very Brief History

Written by Evan Quinter

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Figure 1 illustrates what a Devonian mesophotic reef may have looked like with sharks and extinct coral species. Photo credit to Dr. Zapalski et al. 2017

Serving as the ecological and literal foundation for marine ecosystems around the world, corals are one of the most vital species in the ocean. Corals are found from the shallow coastlines to the dark deep sea, and it’s hard to imagine our oceans without them. But how long have corals been building reef ecosystems; when did the first coral appear? To find out, we need to travel back 500 million years to the Cambrian Period. 

Reconstruction of the Cambrian ocean, with trilobites and early vertebrates
Figure 2 depicts the ocean during the Cambrian explosion, a period full of trilobites! Photo credit to Katrina Kenny, 2019 

Earth at this time was exploding, in a good way. The Cambrian explosion had just unleashed new life onto the planet with almost every major phylum, except Bryozoa, appearing at this time. It was during this biological golden age that coral are thought to first appear as solitary organisms. But after a numerous extinction periods, it’s difficult to find traces of fossilized coral skeletons.

This leads us to the oldest known coral reef, dating back 390 million years to the Devonian Period. The Devonian is known for Tiktaalik, considered the evolutionary link between lobe-finned fishes and early amphibians. But it was also a period of extensive reef-building, which is confirmed by the discovery of mesophotic reefs in the Świętokrzyskie Mountains

Now found in Poland, researchers analyzed platy corals that would have grown at tropic latitudes on the southern shelf of the supercontinent Laurussia. Platy corals often dominate mesophotic reefs, or reefs with middle to low light intensity, as their flat/wide morphology is optimal for environments with lower light. When compared to branching corals that dominate in high light zones, this gradient of coral shapes shows the influence of light availability on species fitness. Moreover, platy corals provide evidence for an early symbiotic relationship with a photosynthetic algae, though it’s unclear if archaic corals utilized zooxanthellae for energy like modern coral.

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Figure 3 illustrates various constructions of Platyaxum corals found in Devonian reefs. Photo credit to Dr. Zapalski et al. 2017

These ancient reefs are a mix of the old and new, with extinct corals living amongst sharks and rays! The types of corals, from the platy Roseoporella to the cone-shaped solitary rugose corals, demonstrate the variety of life present during this time. Unfortunately, the Devonian Period ended with mass fluctuations in climate conditions and a loss in coral reefs.

Modern stony corals (Scleractinia) began to appear during the Triassic period, along with the breaking up of the supercontinent, Pangea. Somehow surviving further Ice Ages and extinction events, these reef-building corals continue to support our modern-day ecosystems. With a history as evolutionary and storied as coral, it only emphasizes the importance of these tenacious animals. As we work to conserve coral from anthropogenic activities and a sixth mass extinction event, remember that we’re protecting organisms who persisted under the sea for millions of years. 

You can find Dr. Zapalski’s study here:

https://link.springer.com/article/10.1007/s00338-017-1575-8

If you’d like to learn more about the geological time scale, click the link below: 

https://ucmp.berkeley.edu/help/timeform.php

To learn more about how scientists measure the age of corals, click the link below:

https://www.whoi.edu/know-your-ocean/ocean-topics/ocean-life/coral/dating-corals-knowing- the-ocean/

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