Coral reefs inhabit less than 0.1% of the world’s oceans but are some of the most productive and diverse ecosystems on the planet.
Calcifying creatures such as corals and species of algae form the base of the reef. Through their continuous growth and deposition of layers of calcium carbonate the reefs form and slowly but steadily grow.
Although the coral skeleton is made of calcium carbonate, essentially limestone, it is very brittle and easily broken. Fragments of coral skeleton pile up and over time consolidate into a connected structure. This forms the solid base upon which the new corals settle and build more reef! These reef structures, if left undisturbed, can grow to be enormous. The Great Barrier Reef in Australia is a complex of coral reefs that stretches for more than 2,300 kilometres (1,400 miles) and in Belize and the Bahamas, there are reefs that are hundreds of kilometres long.
The main constructors of these reefs are the Scleretinian Corals, also known as hard corals. The coral structures are actually colonies of tiny coral polyps. These polyps vary in size depending on what species it is, but they are typically about 2mm. If you consider how many of these small organisms it would take to construct a single coral colony, imagine how many are involved in the construction of an entire reef!
The complex structures formed by the reef building organisms provide habitats for many other creatures. Small fish, crabs and shrimp find safe places to hide in little holes, under ledges or amongst the living branches of the coral colonies. Larger holes make excellent places for small sharks or turtles to sleep. Large overhangs or caves can be filled with schools of fish. Large predatory fish such as Barracuda or Jacks patrol over the reefs looking for prey. Even the largest creatures that spend most of their lives in the open ocean will visit the coral reefs from time to time. Manta Rays and Thresher Sharks for instance, regularly visit the reef to be serviced by various species that will remove parasites or even clean wounds. Other species of fish that spend their adult lives in the open ocean will grow up on coral reefs. These are just a handful of the thousands of ways that species of all kinds rely on coral reefs in some way. It is an ecosystem of staggering complexity and natural beauty.
Without coral reefs, many of the most attractive areas in the world would not exist. Coral reefs benefit humans in several ways:
These amazing corals face many threats, damage from poorly managed tourism, bad fishing practices (such as fishing with poison, dynamite or trawlers), over fishing, water pollution, climate change and many others. We must all take action to protect these wonderful ecosystems for the future!