Let's talk about corals.

I find that corals are one of the most ecologically important organisms that do not get talked about a lot. Let me ask you something: do you think corals are animals, plants, or just plain lifeless substrates, like a rock?

I'll tell you the answer in a bit.

Diverse reef in Napantao South Wall dive site, Sogod Bay, Philippines
(Photo owned by author)

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Coral Reef Ecology

Coral reefs are the underwater ecosystems built by tiny organisms that produce their own calcium carbonate structures. Basically, the organisms build their own "rock" so that the system becomes sturdy and stable for other organisms to live in. Corals are the tiny colonial polyps that live in between the slots or cups in those calcium carbonate structures and they exist only when a certain set of conditions have been met.

First of all, they can only grow where they are able to withstand currents. If the currents are too strong, corals could break and die. They can also only exist in the right range of temperature. If it is too hot or too cold, the polyps would be under stress and would eventually get killed. That is why coral reefs can only thrive in the tropics.

Encrusting corals is a great sign of a growing reef. Talima, Olango Island, Philippines
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Corals can only exist where there is ample sunlight. It means that they do not often exist in deeper parts of the ocean because sunlight can no longer penetrate that region. Coral polyps do not directly need sunlight but these polyps have a symbiotic relationship with an algae called zooxanthellae, a microscopic plant-like organism that live on the polyp, and it is the zooxanthellae that needs the sunlight. The zooxanthellae converts sunlight into food which is also the major energy source of the coral polyp.

Let's go back to my first question. Is a coral an animal, plant, or a rock? The obvious and correct answer would be an animal. However, if you see it systematically, a coral is actually an animal fed by a plant and produces its own rock. It's all of the above options!

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The Importance of Coral Reefs

We may think that corals and reefs don't really matter to us but I'd like you to think again. Coral reefs are homes not just for fishes but also for millions of marine organisms. They maintain the equilibrium in the marine environment. They can serve as protection to the coastlines from storms and wave action. They provide nitrogen and nutrients for the marine food chain. They assist in trapping carbon from the atmosphere thus mitigating the effects of climate change.

Sunny day looking out to the deep blue at Tanon Strait, Philippines
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Threats to Coral Reefs

Coral reefs are under threat. If you could remember me saying a few paragraphs ago, coral reefs need the right temperature in order to grow. However, with the increasing ocean temperature, corals are being pushed to their limits. Once they are under the stress of extreme heat, they no longer have the energy to hold on to their zooxanthellae symbionts. This causes the corals to release the algae and thus their colors. If you see corals that are white like chalk, it means that they are under stress and about to die. This condition is called coral bleaching.

Measuring the health of corals based on a color chart by Coral Watch. Coral fragments were named after the people working on the project. This one shows the coral named "Andrea" which is actually my first name.
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Another threat to the corals is brought about by a condition also commonly caused by humans. Corals cannot exist in places with high nutrient contents. Nutrients are food for fast-growing algae so they tend to overpower nutrient-rich waters. When algae grows, they consume the food and energy source of the area and they overshadow the corals and prevent them from growing. Nutrients can get into the water every time we dump waste water, sewer drains, human effluent, and agricultural run-off. If we are not careful about what we allow to flow into the sea, we end up feeding algae and killing corals. Just think of what has happened to Boracay Island.

A tourist standing on a massive Porites coral. Moalboal, Philippines
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Another threat to coral reefs is irresponsible tourism. Many people think corals are just rocks so it would be okay to step on them. That is a big misconception that we have to break away from. If we stand on corals, we kill a few hundred polyps that could have supported a thousand more microscopic organisms.

If we humans are not wary of our actions, we will be endangering our reefs and in turn will also threaten us and the ecosystem.

Of course, we wouldn't want that. Corals are animals and they have feelings too.

Please be a responsible earthling.

Working on our coral nursery at the Coral Cay Conservation Leyte Reef Conservation Project
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Source: Reef Fishes, Corals, and Invertebrates by E. Wood and M. Aw, published by New Holland Publishers (UK) Ltd., 2002

Cheers,
Xayd