What can coral skeletons tell us about the past? 

Did you know corals hold clues to the past—just like tree rings?

During our  May expedition to Tela Bay, multiple science projects were happening at the same time as we were shooting The Rebel Reef documentary. Besides the Matz Lab coral genetics team from UT Austin, scientist Jonathan Jung from the Max Planck Institute in Germany also joined us. Jonathan teamed up with Tela Coral to take a closer look at some of our oldest and biggest brain and boulder corals. These corals grow slowly, adding new layers year after year, sometimes for centuries. Each layer holds tiny chemical clues about what the ocean was like when that coral was growing.

By carefully drilling a small core from these corals, (don’t worry, it doesn’t hurt them!) researchers can study those layers to learn about past ocean temperatures, rainfall, pollution and other environmental changes. It’s like opening a hidden time capsule from inside the corals!

Why study coral histories?

Coral reefs all over the world are under threat—from warming oceans, pollution, overfishing and diseases. But not all reefs have had the same experiences. Some, like ours in Tela, seem to be doing surprisingly well despite tough conditions with much turbidity and high nutrient water runoff from the land.

This is why Jonathan came to Tela. He wanted to know:
Could our corals be stronger because they’ve been exposed to these challenges for a long time? If so, it could help explain why the reefs here still look so healthy—when many other reefs in the Caribbean have been dying off.

“May these reefs of hope reveal their past to guide us into a brighter future”

 – Jonathan Jung

What’s next?

Now that the coral cores have been collected, they’ll head back to Germany for detailed lab analysis. The scientists will slice the coral rock into thin layers. Each layer will be analyzed for their isotopes. 

Isotopes are forms of the same element that have different numbers of neutrons. For example, most nitrogen on our planet has 7 protons and 7 neutrons (mass 14), but a small percentage has 8 neutrons (mass 15). The coral uses nitrogen to build its skeleton, preserving those isotopes in rock that we can read through time. If a skeleton layer has more nitrogen with the mass 14, it means the algae were providing more nutrition; if there’s more of the nitrogen with mass 15, it means the coral were eating more zooplankton.

The stable isotopes will tell us if Tela’s coral are feeding differently than coral in other places, which might be a reason why they bleach less often and usually recover. They will also tell us how this feeding behavior might have changed over the decades. And those are just a couple of the questions we can answer with stable isotopes. 

We’re excited about this work, which will help to uncover more of the story of Tela’s reef—how it has changed, why it has survived, and what that means for the future of coral reefs everywhere.

Stay tuned—we can’t wait to share what we find!