Ocean Insights

What are corals?

Some may compare underwater reefs to a rainforest, where coral would play the role of the tree. While coral does lay the foundation for a thriving ecosystem, much like towering trees with plenty of vacant residences for critters, corals aren’t plants like this comparison would suggest. Coral is a living animal. Related to jellyfish and sea anemones, they belong to the phylum Cnidaria and class Anthozoa.

landscape of a coral reef in Timor-Leste

Most species of coral are colonial animals, meaning that individual polyps gather together, forming groups of a few hundred to over a hundred thousand animals. Each polyp is cylindrical in shape and contains tentacles surrounding one mouth opening that leads directly to the stomach. To eat, they use the tentacles to catch nearby organic debris, zooplankton, or small fish and move them toward their mouth for digestion. Colonial corals may share connected stomach cavities and can transfer food to other polyps in their group. But for the majority of their energy and nutrient uptake, they rely on a mutually beneficial relationship with zooxanthallae, a microalgae organism that lives in coral tissues.

Corals can either be hard or soft. In a reef ecosystem, one may find soft corals among the populated habitat, but the structures that provide the reef’s foundation primarily consist of hard corals. Hard polyps congregate and form structures with a calcium carbonate skeleton. Their shape creates natural nooks and crannies where various animals attach or find a home. Complex reefs draw thousands of species together and create a lively underwater community!

Swim through the reef and witness the abundance supported by coral animals in our Marine Museum episode on YouTube!