Coral reefs as an example of a Complex Adaptive System and their links to the Climate System

I’ve brought you to an aquarium because I wanted to take a look at a tropical coral reef in order to talk about a tipping point that takes place out in nature. So, the first thing I want to present is are corals that create the foundation for coral reefs. These are animals that are quite formidable because alone they’re tiny, but they build colonies that together can create entire coral reefs. So, the Great Barrier Reef reaches almost 2000 kilometers in length. and the Mesoamerican coral reef in the Caribbean reaches 1000 kilometers. And these reefs have lasted for a long time.

So the Great Barrier Reef is about 8000 years old as we know it today, but it existed for tens of thousands of years before that, as well. And the important thing to know about coral is it’s an animal.

It lays a skeleton of calcium carbonate that on the ground, on its surface, and then the coral lies on top of it. And the coral wants nutrient poor waters. And that’s because the coral gets its color, not from itself, but from a microscopic algae zooxanthellae that lives inside of it. So they have a symbiosis. The zooxanthellae gets protection and the coral gets food.

So if we zoom out, we have these large colonies creating large reefs that have lasted for thousands of years. But that doesn’t mean that nothing happens and there’s no disturbance on these reefs. They’re in the tropics and they are subjected to tropical storms and hurricanes. And when those happened, there are large, powerful waves that hit the reefs, often knocking over coral and clearing surfaces. Now this new surface is actually dead coral. and the surface slowly gets repopulated by things that settle down on it and grow, mainly coral. Because these reefs are 80% covered by coral. And that’s the natural progression on reefs.

So, there will always be some disturbance, but overall the reef is much as we expect to see it. So what happens when humans disturb the system? I’m going to tell you a story from the Jamaican reefs in the Caribbean.

In around the 1960s commercial fishing took off on the reefs and the fish first targeted were fish-eating-fish. And as those became a little bit scarcer, they moved down the food chain and start fishing plant eating fish. Now why does that matter? Well, the plant eating fish, they control the growth of seaweeds and algae on a reef. Now, another change was taking place at the same time- -in Jamaica. Increased population meant there was more agriculture needed. Areas were being cleared for agriculture using fertilizers and the coastal vegetation was being cleared. That means that when it rains, the runoff comes down the land and reaches our coral reefs.

Now, corals like I said, they want nutrient poor waters, so the water is nice and clear, so the zooxanthellae can photosynthesize.

When this change came, we actually passed a tipping point. And exactly what was the cause if it’s the nutrient balance, the loss of herbivores or a mixture of both? We can’t be sure. But the next time a hurricane came through, those cleared areas did not get repopulated by coral. Instead, they were taken over by seaweed. And that has persisted. There was a tipping point that was passed that meant that corals were no longer able to dominate this environment. And with that, we get a loss of fishing, which affects livelihoods, food, tourism. Over time, the reef, as it’s no longer being maintained and built upon, will lose its function of wave protection for the island.

So this has serious implications for the people of, in this case, Jamaica. And this has happened throughout the Caribbean, and similar changes have happened on reefs around the world. So, we also need to remember that coral reefs are not isolated from other systems in the ocean. A huge number of the fish and other marine species that we rely on for food actually spend part of their lifetime on the coral reef. So if we lose the coral reef, there will be impacts around the oceans affecting other ecosystems without us even being aware of these changes.

Now, I want to connect our coral reef to other tipping points identified around the planet. As temperatures increase, we know that the sea ice is melting As it melts, the albedo decreases. That means the Earth’s surface is getting darker and it absorbs more heat, which means the temperature rises. As the temperature rises, our coral reefs are getting stressed by the increased temperatures. We have mass mortality of coral reefs, and as I said earlier, loss of the coral reefs are going to affect us in more places around the oceans, affecting our food sources. That means that there’s a connection between the Arctic sea ice, our coral reefs, and all of us, for food.

And we’re also feeding back because our activities are the source of the increased temperature that’s causing the melting of the Arctic sea ice.

All systems are connected.