Plant, animal or other? Coral

Most of us know coral when we see it and I think everyone has probably seen a picture of a coral reef at some point but what exactly is it?

An individual coral is a polyp, a very small, simple creature which has been described as essentially just being a stomach and a mouth surrounded by tentacles.  Living inside the polyps are algae which provide the coral with food and gives it colour. Thousands of identical polyps live together in a colony and this forms the reefs we are familiar with.  Different coral grow at different rates but to form a reef takes a very long time, with estimates for todays reefs being started 5-10,000 years ago.  That being said, not all coral are reef builders.

An alternative take on the creation of reefs comes from Greek mythology.  It was said that they were created from the blood that was shed when medusa was decapitated.  This blood mixed with the seaweed to create the stone reefs.

“With no Pharaoh to lead them, this army of tentacled midgets has built the greatest of the ocean’s wonders, working together for millions of years on their mighty projects.”
– Jeffrey Levinton

Cooperation is a theme amongst the creatures of the reef.  A symbiotic relationship between coral and algae allows the reef to grow and provides the coral with their colours. Coral reefs are home to lots of organisms and provides cracks and crevices for fish and crabs to live in.  So when a starfish comes along and attacks the coral, the fish and crabs step in and defend it.  This allows the coral to keep growing and creating more cracks and crevices for future fish and crabs.  There are also fish which ‘farm’ on the coral, growing algae and in doing so, they are creating ideal conditions for more coral to grow.  And then there are the cleaner wrasse; fish which clean other fish, a service which improves the health of the sea life around the reef.

“No other marine habitat shows so well the intricacies of biological interdependency”.
– Jeffrey Levinton

But despite this incredible interdependency, the reef is a dangerous, cut throat world.  Coral use barbed, venomous tentacles to catch zooplankton and tiny fish and they can also extrude their stomach and digest neighbouring coral…

The competitive nature of the habitat means some coral dwellers have developed nasty chemical defences.  For example, the sea squirt makes sulphuric acid to burn predators and also a poisonous metal that could kill a horse.  The sea whip produces higher amounts of prostaglandin than other creatures making them taste terrible to most predators (although a type of snail and worm can eat them).  Poisonous fish live among the coral and sharks patrol the edges.  This beautiful underwater garden can be a deadly place.

But those deadly poisons and chemicals may actually be of use to us.  We may be able to use some of them to develop cancer cures, to help neurological diseases, to treat infections and to fight drug resistant bugs.  Corals themselves can be used in bone graft surgery as well.

As well as medical value, coral reefs provide coastal defences, tourism, food (an estimated 0.5 billion people rely on coral reef fisheries worldwide for 95 percent of their protein) and jobs.  The Great Barrier Reef has been valued at at AUD $56 billion, contributing 64,000 jobs and $6.4 billion a year to the Australian economy.

But despite their importance, we are not treating them kindly.  Coral reefs are threatened by overfishing, pollution, invasive species and ocean warming and acidification caused by rising carbon dioxide levels.  In the last 30 years, we have lost 50% of the coral and scientists predict that we will lose 90 percent of coral reefs globally by the year 2050.

This would be catastrophic.  Life on the reef is a diverse one, paralleling that of the rainforests.  Apparently, despite reefs covering less than 1% of the earths surface, a quarter of ocean biodiversity depends on reefs for food and shelter.  Without the reefs, the health of the ocean will suffer and without a healthy ocean, we cannot have a healthy planet.

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