Constructing a Coral Reef

Constructing a Coral Reef

Tropical coral reefs are amazing underwater habitats. Known as rainforests of the ocean, coral reefs have over 4,000 species of fish and support 25 percent of marine species at  one point in their life cycles. Coral reefs did not suddenly appear in the ocean but were built step-by-step by various animals over millions of years to become the habitats that they are today.

Over time, reef species have changed but the functions and roles of the different species have remained similar. In this video, we will have a general overview of how the ecosystem is built, showing some of the major plant and animal groups that are part of these complex systems.

Scientists from around the world work together to study all the plants and animals that live in these reef systems, so they can better understand changes over time. Here our scientists present step-by-step how the biodiversity of a reef system is built. Let's go over the different groups now.

First, stony corals or hard corals are what create the foundation of the reef. A reef is started when the free swimming coral larvae attach to hard surfaces along the edges of islands or continents and start to grow. These tiny animals are called coral polyps and they create tiny stone skeletons to live in. They take calcium carbonate, the same mineral that makes up chalk and shells, from the water to form the mineral skeleton. These animals live in colonies that form large stony coral structures. As living animals they provide structure and a food source and once the polyps die their hard skeletons still contribute to the reef by adding complex structure and habitat for other plants and animals.

There are over 3,000 species of stony corals, coming in all sorts of shapes and structures. The more complex 3D space a reef has, the more life it will attract.

Once stony corals are established, soft coral and sponges will come in and attach themselves  to the new hard surfaces the stony corals have created. The soft corals are related to stony corals, but do not create a calcium carbonate skeleton. Sponges are animals; they have bodies full of pores and channels that allow water to filter through them to feed.

These flexible animals add complexity and color to a reef. Like the soft coral, different types of algae depend on a hard bottom to land on and provide protection from the waves. They grow here and provide an important food source for animals that live on the reef.

Speaking of animals, small invertebrates, or animals without backbones, are another important group on the reef. They will eat the algae, soft corals, and sponges and will also use the coral reef structure as shelter to hide from predators.

Also attracted to the algae and coral are herbivorous fish, which eat plants, and corallivorous fish which eat coral. These fish will eat the algae and coral, which helps maintain the structure of the reef.  

Then come the mid-level predators: the carnivorous fish that will eat the smaller animals. These carnivorous fish keep the herbivorous 
and coralivorous fish and invertebrates in check so they do not eat all the algae, coral, and sponges.

And finally, top level predators are animals that prey on the carnivorous fish and are attracted to all the life that is in a coral reef. The top predators also contribute in keeping balance in the coral reef food chain.

Coral reefs are complex habitats that are home to many different marine species. Let's recap the different groups of plants and animals that make up a coral reef ecosystem. Can you recall each group's major function?

Let's go over it. To start stony coral make up the reef foundation, and then the soft coral and sponges add to the structure. The algae adds to the structure and is a food source. Small invertebrates eat the coral and algae. The herbivorous fish and coralivorous fish eat the coral and algae to maintain structure. 
Mid-level predator fish eat the smaller animals, and finally the top predators maintain balance in the food chain by feeding on other reef species.  

Well done! Now you know the general structure of tropical reef systems. There are many different groups involved that are in balance with each other, and if there is an imbalance, for example if stony coral die, other organisms like algae or soft corals can take over the space that is left behind. Understanding how these reef systems are constructed helps scientists ask questions and investigate when the reef is out of balance from impacts of climate change, overfishing, pollution, and even disease. By understanding these systems we can help protect them better.