Coral reefs: rainforests of the sea

By Cynthia Ann Shannon, Atlantic Science Enterprise Centre

Coral reefs – often called “rainforests of the sea” – are the most diverse underwater ecosystems. And since I didn’t really understand what a coral was when I started writing this, I’m going to guess some of you don’t either.

Corals are marine invertebrates. That means they have no vertebral column/spine. They typically live in compact colonies of many individual polyps. The group includes the important reef builders that inhabit tropical oceans and secrete calcium carbonate (the main component of pearls and snail shells) to form a hard skeleton. 

But cold water corals can be found off eastern Canada, in a range of depths, substrates and currents. About 25 to 30 coral species live in waters off Atlantic Canada, most of them in depths of 150 metres and greater. Several of these species are long-lived and grow to greater than one metre. And at least one can form reefs.

Corals are generally found along the edge of the continental shelf and in deep channels between fishing banks. Visit the DFO page on Cold-water corals and sponge reefs for further information on corals in the Maritimes.

Whether in a group or as an individual, corals provide structural habitat for other marine creatures by providing a place to rest, feed, spawn and avoid predators. In deep, dark waters, coral communities may present the only habitat forming features on the seafloor.

Coral reefs consist of an accumulation of individual polyps arranged in different shapes. Polyps can range in size from a pinhead to 30 cm (12 inches) across. Most coral reefs are built from stony corals. The hard carbonate exoskeletons secreted by the corals support and protect the polyps.

While they occupy less than 0.1% of the world’s ocean surface, they provide a home for at least 25% of all marine species, including fish, mollusks, worms, crustaceans, echinoderms (creatures with a hard spiny covering such as sea stars and urchins), sponges and seabirds.

Most coral reefs we see today were formed after the last glacial period (c. 110,000 – c. 11,700 years ago) and so are less than 10,000 years old. That’s pretty young in the overall scheme of things.

The value of coral reefs has been estimated at a minimum of $39 billion a year, providing food, tourism jobs and even medicine, as coral reef organisms are used in treatments for diseases such as cancer and HIV. Unfortunately, while reefs are important to us, we pose the greatest threat to them.

So coral reefs are dying around the world. Coral mining, agricultural and urban runoff, and water pollution – all threaten these ecosystems. Coral reefs are also fragile because they are very sensitive to rising water temperatures. Other threats include increasing sea levels and pH changes from ocean acidification – both associated with greenhouse gas emissions.

Stay tuned to learn what the Government of Canada is doing to help conserve not only corals but sponges as well.