Coral reef | Nature Adventure

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Biology

You might think that corals are plants. They certainly look like plants, don't they? They don't move, have leaf-like structures (even though they're hard as rocks!), and come in so many vibrant colors! But surprisingly, corals are actually animals. They're the cousins of creatures like jellyfish and sea anemones, a phylum called the Cnidarians.

Cnidarians have a circular body with a very simple stomach and just one opening for both food and waste. This opening is surrounded by special tentacles with cells called nematocysts, which have countless microscopic stingers, just like a jellyfish's arms!

Even though corals are technically animals, they're extremely unique animals. Cnidarians can restructure and regenerate their bodies countless times, meaning that some corals are over 5,000 years old! They start off as little polyps that congregate into colonies, making giant reefs that support an enormous variety of ocean life. One "single" coral is actually made up of thousands of individual polyps all stuck together; they're just so small that you can't usually see them!

There are both soft and hard corals, but the ones we are most familiar with are the hard coral varieties, which grow an exoskeleton of calcium carbonate. This is what makes them feel and look like rocks! Almost like a snail's shell, the soft body of the polyp is protected by this outer layer.

Ecological Importance

Coral reefs create vital ecosystems for numerous sea creatures, from the clown fish that live inside of stinging sea anemones (a relative of the corals!), to eels that use the reefs as a hunting ground, to so many other fish species that rely on the reefs for protection and food. They also make the water cleaner, since corals feed off of debris in the water.

Though coral reefs are only 1% of the entire ocean, they provide a home for over 4,000 species of fish and around 25% of all marine life! This is more than any other ecosystem in the entire world! And human being also rely on corals, too. Many of the fish we eat use reefs for shelter and food. If we loose the reefs, many people will lose their main source of food.

Unfortunately, most of the reefs around the world are dying. This is caused by a few factors, but one of the biggest is simply the effects of climate change. Since corals construct their protective outer shells from calcium carbonate, the process of ocean acidification (caused by atmospheric CO2 entering into the ocean water) actually dissolves this outer skeleton, leaving them weak and brittle. And, in high temperatures, corals will eject the helpful algae that normally live in their bodies, turning them completely white! These two factors combined means that vast areas of coral reefs are dying out faster than they can adapt to these new environmental changes.

Marine biologists are invested in protecting the coral reefs, and are trying all sorts of new techniques to minimize the damage being done to them. And they are making a difference! The Great Barrier Reef, the largest coral reef in the world, has seen a gradual increase in coral growth in 2023. This new growth comes with its own problems, but it's through the dedicated efforts of these biologists that we still have reefs today, and may hopefully have them for many thousands of years to come.

Did you know?

Corals can only photosynthesize with the help of an algae called zooxanthellae!

Photosynthesis is the process where sunlight is converted into energy. Since corals are animals related to jellyfish and anemones, they can't normally do this on their own. They need the help of something that can photosynthesize, like little single-celled algae! These zooxanthellae live within the cells of the coral itself, almost like the mitochondria of our own cells. They produce energy for themselves and transfer the rest - up to 90% of the energy they make! - into the corals tissues, helping them grow. This relationship is mutually beneficial, as both parties (the coral and the algae) benefit positively from this arrangement.

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