What are Corals?

More than 97% of the world’s animals are classified as invertebrates, animals without a backbone, ranging from ocean-dwelling corals, jellyfish and sea stars to spiders and insects. Corals are related to jellyfish and anemones, and rank among the largest and oldest living communities on Earth. One coral colony is made up of a community of genetically identical individuals, called coral polyps, that all work together to obtain food and protect one another. Coral polyps consist of a columnar body with stinging tentacles called nematocysts that surround their mouth. 

 

These polyps also contain large numbers of marine algae, zooxanthellae, in their tentacles. When zooxanthellae and corals live together, they establish a symbiotic relationship, meaning that both organisms receive a mutual benefit. These zooxanthellae are plants, and therefore perform photosynthesis, using the sun’s energy to make sugars. Corals eat these sugars and in return, the corals provide protection and produce waste products the zooxanthellae digest. Since these symbionts need light for photosynthesis, corals typically grow in ocean waters less than 100 meters deep. This symbiosis drives the entire biological productivity of the coral reef ecosystem, allowing corals to grow and maintain their structure and ecosystem function.

 

These polyps only make up the upper layer of the reef colony. These animals secrete calcium carbonate (limestone), which they mold into tiny, cup-shaped homes that the polyps are attached to. These homes form the hard structure we know as reefs and provide a rich habitat for hundreds of thousands of other species. Corals vary in size, shape, and color and are found around the world in warm, tropical waters. Despite the wonder these ecosystems bring, they are starting to decline rather quickly due to climate change impacts.