The colonies of the ocean | Marine Biology

May 02, 2021

A group of corals are known as colonies. Corals are large structures, held together by Calcium Carbonate. This calcium carbonate is extracted from the seawater to create a durable exoskeleton to protect their soft bodies. There are about six thousand species of coral around the world, with some species growing in warm shallow waters near coastlines and others thriving on the dark, cold seafloor of the open ocean.

Each individual coral is referred to as a polyp. Coral polyps live on the calcium carbonate exoskeletons of their ancestors, adding their own exoskeleton to the existing coral structure. As the centuries pass, the coral reef gradually grows, one tiny exoskeleton at a time, until they become massive features of the marine environment.

Coral polyp bodies are usually clear. The bright colours that characterize many corals are actually various types of algae growing in the polyp’s tissue. Several million zooxanthellae live and produce pigments in just one square inch of coral. These pigments are visible through the clear body of the polyp and are what gives coral its beautiful colour. The zooxanthellae are light sensitive, increasing or decreasing based on available light intensities, and as a result becoming darker or lighter.

Zooxanthellae

The coral provides the algae with a protected environment and compounds they need for photosynthesis. In return, the algae produce oxygen and help the coral to remove wastes. Most importantly, zooxanthellae supply the coral with glucose, glycerol, and amino acids, which are the products of photosynthesis. The coral uses these products to make proteins, fats, and carbohydrates, and produce calcium carbonate. The relationship between the algae and coral polyp facilitates a tight recycling of nutrients in nutrient-poor tropical waters.

Coral reefs not only provide marine species with a rich habitat, but they also assist people as well. Millions of people around the world rely on fish caught in and around coral reefs. The reefs also draw in tourists, which helps the local economies. Coral reefs protect people and land from storms as well, serving as a barrier that reduces the impact of large waves on shore.

There are 4 main types of coral structures, table, boulder, branching and pillars.

Table corals

Table corals are corals that form broad horizontal surfaces. This pattern of growth increases the exposed surface area of the coral to the water column. Polyps are provided greater access to light for their zooxanthellae and it is easier for them to feed on zooplankton with their tentacles. “The loss of table corals denies fishes important habitat, which they use to shelter from the sun, avoiding harmful UV-radiation, just as we might sit under an umbrella at the beach,” says study lead author James Kerry.

Boulder Coral

Boulder corals are a species of stony coral found primarily in the Caribbean Sea and the Gulf of Mexico. It inhabits the slopes and tops of reefs, to a maximum depth of fifty metres. It is characterised by large, domed colonies, which may be up to two metres across, and by the meandering network of ridges and valleys on its surface.

Branching corals are characterized by having numerous branches, usually with secondary branches. This large field of branching corals belonging to the family Acroporidae was observed in the French Frigate Shoals, one of the many reefs that make up the North-western Hawaiian Islands.

Pillar Coral

Branching Corals

Pillar coral is a hard coral found in the western Atlantic Ocean and the Caribbean Sea. It often resembles fingers or a cluster of cigars, growing up from the sea floor. Pillar coral is listed as threatened under the Endangered Species Act.

Coral reefs protect coastlines from storms and erosion, provide jobs for local communities, and offer opportunities for recreation. They are also are a source of food and new medicines. Over half a billion people depend on reefs for food, income, and protection.

Because of the diversity of life found in the habitats created by corals, reefs are often called the "rainforests of the sea." About 25% of the ocean's fish depend on healthy coral reefs. Fishes and other organisms shelter, find food, reproduce, and rear their young in the many nooks and crannies formed by corals.

No matter how much we know about the good corals do for us as humans, and for the environment, there are so many threats that endanger corals and along with that, the life that survives solely because of the reefs. There are so many issues that we need to address like bleaching of corals and fishing, which also heavily affects coral life. Stick around to read about Coral bleaching next.

If you enjoyed reading this, you might like my previous post on Planktons, check it out !

https://musings-of-a-musical-biologist.blogspot.com/2021/04/whos-at-bottom-of-food-chain-marine.html

Citations:

What are corals?

https://www.livescience.com/40276-coral-reefs.html

https://www.nationalgeographic.org/encyclopedia/coral/