Coral on the Great Barrier Reef

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Bleached but not beaten; coral is still Great on the Barrier Reef

Tell me something cool

Coral is an animal. They look like some sort of plant, but they are actually an animal. The branches we call coral are actually made up of thousands of tiny animals called polyps. They are an insect (invertebrate) that ranges from the size of a pinhead to 30cm.

Amazingly they have a type of plant (algae) that live in perfect harmony inside them called zooxanthellae. The coral provides a home and the algae provide the food. Like house mates – one has rich parents who bought the place and the other pays rent by buying the food.

Both of the organisms spew stuff out. The coral polyps spew out a hard stony substance made from the calcium from the seawater – limestone. While the algae spew out sugars which the polyps gobble up.

It is actually the algae that gives the coral the colour. So the housemate keeps the place looking good too.

So how do coral polyps, algae and reefs come together to form the Great Barrier Reef? Ok we will break it down further.

Out in the ocean there are lots of rocks and we call them reefs because they’re under water. If they were above water we’d just call them rocks. On these rocks, coral take hold and start spewing out limestone. This all creates an attractive home for the algae who come and start cooking up a storm. Then they both grow and reproduce and become forests of coral covering the reef.

There are something like 600 types of soft and hard corals which are not only homes for the algae but also for a breathtaking array of marine animals including more than 100 species of jellyfish, 3000 varieties of molluscs, 500 species of worms, 1625 types of fish, 133 varieties of sharks and rays, and more than 30 species of whales and dolphins.

Where do they live?

The Great Barrier Reef and the coral that live on it is not one continuous reef, but made up of over 2900 reefs and 900 islands. The Reef stretches 2300 kilometres from the top point of Australia – the tip of Cape York Peninsula in the north and extending down to Bundaberg in the south. The Reef is so large it can even be seen from outer space.

Tell us about their history

The coral on the reef have been doing fine for the past 500,000 years but for the past 20 years they have been struggling. You might have heard about this on the news – coral bleaching is happening and putting the coral and the Reef on the edge.

Coral bleaching occurs when sea temperatures rise (due to global warming) or the water quality isn’t top grade which cause corals to kick out their housemates the tiny algae. It gets too hot in there and they leave. Then the corals true colour is revealed – translucent polyps and the white limestone houses – and so they looked bleached.

Corals which have only kicked out a few of their housemates can recover when the temperature drops again and the water quality improves, but if it doesn’t, the coral will struggle to grow again or die because it has no one bringing in the food. It can take decades for coral to recover after bleaching.

The Great Barrier Reef has lost more than half its coral cover since 1985. A 2016 report stated that the reef was experiencing widespread coral bleaching as a result of warming ocean temperatures. In fact as much as 93% of the Reef is bleaching.

While we can’t immediately cool down the ocean temperature, we can do something to help improve the water quality. Healthy wetlands across the 35 catchments draining into the Great Barrier Reef are critical to reverse the decline. Wetlands have the ability to slow the water flow, absorbing pollutants, trapping sediments and cycling nutrients before they enter the Great Barrier Reef lagoon. For example, some wetlands have been found to reduce the concentration of nitrate by more than 80%.

What is putting them on the edge?

Warmer water and poor water quality are the two biggest issues putting coral and the Great Barrier Reef on the edge.

Poor water quality puts additional stress on coral and warmer ocean temperatures can then lead to coral bleaching. Coral likes warm water, but not hot dirty water.

Every year, an average of 1.4 million tonnes of fine sediment along with trapped agricultural chemicals and fertilisers pour into the Great Barrier Reef due to river bank and gully erosion in the
Great Barrier Reef Catchment. This is between three and five times more than pre-European settlement and it’s having a significant impact on the health of the Reef.

Too much sediment limits the amount of light that can get through to the coral-algae on the reef while nutrients from fertilisers encourage other algae to grow in the water, which sucks away the oxygen for other animals.

The sediment is suffocating coral and fish and threatening the survival of this fragile ecosystem.

What is the vision for them?

We want to improve the water quality by reducing sediment loads landing on the Reef. We want the Coral to have a healthy environment in which to live so that it can recover from coral bleaching. To achieve this we need to restore the eroding land and rebuild the coastal wetlands.

How much money is needed?

The funds you raise will repair river and gully erosion and rebuild coastal wetlands along the Great Barrier Reef coastline.

· $5,000: We will identify and stabilise hotspots of river bank erosion at key locations along the rivers entering the Great Barrier Reef lagoon.

· $20,000: We will restore one hectare of coastal wetland on areas that have been previously modified to allow farming. This will include fixing up the water flow to and from the wetland and will restore native trees, bushes and grasses that trap sediment and nutrients before discharging onto the Coral.

· $100,000 +: We will work with as many farmers as we can to repair rivers, gullies and wetlands and improve how they manage their farm to reduce the sediment entering the reef and suffocating the Coral.

Want to do more to help?

Go to www.greeningaustralia.org.au

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