Are corals animals or plants?

Coral is a stationary animal that has a unique relationship with plant-like algae called zooxanthellae that lives inside its tissues and together they build the largest biological structures on Earth.

The algae use sunlight to produce oxygen which is beneficial to the coral and in return the coral provides a safe home for the algae and compounds the algae needs for photosynthesis.

So even though corals are an animal, they couldn’t survive without their algae partners. Algae also give the coral its unique colour.

What exactly are corals?

Corals are made up of thousands of ‘polyps’ and some types of corals produce a hard skeleton out of limestone so they are called hard corals and others don’t so they are called soft corals. The components of a polyp are shown in figure 1.

It is the hard corals that build the large reef structures we enjoy snorkelling or diving on, and these reefs often protect sand islands from waves.

The majority of corals are permanently attached to the seafloor by ‘cementing’ themselves to the substrate. They don’t have roots like most plants do. They actively capture food from the water column using their stinging tentacles which then move the food to their mouth. There are around 800 different types of hard corals.

Soft corals on the other hand don’t have the limestone skeleton and instead grow wood-like cores to hold them upright. Soft corals can be more complex and colourful than hard corals and can resemble bushes or trees.

What are the benefits of corals?

Coral reefs have more biodiversity than rainforests and are the most diverse ecosystem in the ocean. They provide enormous financial benefits to us in the form of food, protection from storms and tourism. The Great Barrier Reef generates over 6 billion dollars per year for Australia and employs 64,000 people.

Reefs are the spawning and feeding grounds for much important fish that we catch and eat. If we lose coral reefs, we will see a collapse in a huge number of fish and lobster populations, and many islands will be washed away.

Threats to coral reefs

You may have read or heard the news that the Great Barrier Reef nearly lost its listing as a World Heritage area due to the fact so much of it has died. Rest assured there is still a lot of healthy coral left but a large portion was killed by higher than normal water temperatures. Climate change is increasing ocean temperatures and making the oceans more acidic and these two are the biggest threats to coral reefs. We increase the problem by weakening the health of corals or destroying them directly through development, pollution, bad fishing practices, overfishing, and tourism.

How to save corals?

This is a big question that many are working on and one we teach about at Envirotech. One way is to create more protected areas to reduce direct human impacts and indirect effects such as overfishing.

Addressing climate change by reducing greenhouse gas emissions is the most important as increased sea temperatures and ocean acidification are the death of reefs no matter what else we do. Purchase carbon offsets to help counter emissions from your flights, car, business or lifestyle.

On a smaller scale, we can support groups planting corals back onto degraded reefs or actually participate in the planting ourselves. We can participate in coral surveys to help map reefs and document their health so this information can be used to better manage them. We can choose reef-safe sunscreens because common sunscreen chemicals kill corals. And we can reduce our consumption of fish and meat.