Changes to the Great Barrier Reef

Changes to the Great Barrier Reef

A famous example of a coral reef, the Great Barrier Reef (GBR) is the largest in the world. It covers an approximate area of 133,000 square miles, composing 2900 individual reefs and 900 islands. It is famously so big, that it can be seen from space. 1981 was a big year for the GBR, as it was named a world heritage site, due to the sheer number and diversity of the wildlife supported by these reefs.

Great Barrier Reef at its best, showcasing all its diversity.

This was a massive boost for tourism and visits to the GBR, but in the prevailing 30 years or so, the area has been going through some tough times. On the 28^th November, BBC news reported that due to high water temperatures throughout 2016, 67% of corals had ‘died’ in the northern section of the GBR, as well as 6% from the central section. Despite this doom and gloom, some positive news from the southern part of the reef where the vast majority of the reef remains in good health. This was the worst ever recorded bleaching event in the Barrier Reef’s history and with global ocean temperatures set to rise, this may not be the largest bleaching event for long….

As well as rising temperatures, the GBR faces a threat from the declining amount of coral calcification. This is the result of increased ocean acidification. The level of coral calcification has decreased by 14.2% since 1990, the sample area encompassing 328 colonies from 69 reefs that make up the GBR. This is unprecedented in at least the last 400 years. The impact of a decrease in the amount of coral calcification means coral reefs lose their ability to deposit calcium carbonate (CaCO3). This is important as thousands of coral species derive their structural integrity from creating a calcareous skeleton. The peak year was 1970, where calcification was increasing by 1.76 gcm-2 year-1. It’s been downhill ever since.

And it continues to get worse. Kroon et al, 2012, published a paper stating extensive nitrogen, phosphorous and herbicides had been found throughout the GBR. 80000 tonnes of nitrogen now enters the GBR every year, with phosphorous at 16000 tonnes a year. These inputs into the GBR have come as a result of anthropogenic activity, especially from agricultural sources, urban development and deforestation. The danger of these inputs is that it may lead to eutrophication, hypoxia and reductions in coastal biodiversity. This will affect the coral as well, as the algal blooms will prevent coral from using photosynthesis to feed and will therefore begin to bleach.

As we have seen, the GBR has experienced some testing times, and now it is under threat like never before. The outlook doesn’t look promising, however hopefully there can be success built around the presently healthy southern part of the reef. In summary, coral populations have been on the decrease ever since 1970, due to a mixture of anthropogenic factors. In order to save the Great Barrier Reef concerted effort from Australia and other world powers will be required.

 

Sources

Full BBC article: http://www.bbc.co.uk/news/world-australia-38127320

http://science.sciencemag.org/content/323/5910/116.full (Glenn De'ath et al, 2009)

http://www.sciencedirect.com/science/article/pii/S0025326X11005583 (Kroon et al, 2012)