Great Barrier Reef: the final warning?

                                         Australian Institute of Marine Science

There's been another health report on the Great Barrier Reef, and the prognosis isn't good. Between 1985 and 2012, at 214 reef sites surveyed by the Australian Institute of Marine Science (AIMS) in Townsville, the coral cover – by which the wellbeing of the Reef is judged – halved, from 28 per cent to 13.8 per cent. Two-thirds of that loss happened since 1998; only three of the sites exhibited no coral cover reduction.

Almost half the coral lost was as a result of tropical cyclones (48%). Since we've lived in Queensland there's been one severe (category 5) tropical cyclone to hit the coast, in 2011. Cyclone Yasi was a massive system a long way north of Brisbane: it came ashore on Mission Beach, where we spent an idyllic couple of days on our roadtrip the previous year. There were category 4 or 5 cyclones in 2006 and 2008, the latter wreaking massive havoc on the Reef as it tracked along the coast rather than crossing it. The impact of such an event on land is visible immediately, but the damage done beneath the ocean's surface receives less attention until a Reef report like this is published. AIMS scientists compiled The 27-year decline of coral cover on the Barrier Reef and its causes* for publication by the Proceedings of the National Academy of Sciences (PNAS) in the US. The two images below show the MacDonald Reef before and after a cyclone (courtesy of Katharina Fabricius, AIMS).

Only slightly less damaging (42%) to the Reef than cyclones were Crown of Thorns Starfish (top of page). These native creatures fluctuate in numbers, exhibiting 'outbreaks' every few years that have a devastating impact on coral reefs. With as many as 21 arms and a diameter of up to 45 cm, COTS have few predators as they are covered with spines containing a virulent toxin. They feed on live coral: one starfish can consume ten square metres of coral a year. Outbreaks occur about every 14 years, and the last one was in the late 1990s. It has been suggested that human activity could be exacerbating these outbreaks. COTS larvae feed on plankton that thrives if increased nutrients are available. This happens following big rains that carry agricultural products into rivers and hence the ocean. The photographs below show the Horseshoe Reef before and after a COTS invasion (courtesy of the AIMS Long-term Monitoring Team).

Ten per cent of coral loss was due to 'bleaching', which is a sign of coral under stress. Corals are minute marine organisms that secrete calcium carbonate to form a protective shell. These polyps can catch fish and plankton to eat but mostly obtain nutrients and energy from algae (zooxanthellae) that live within the coral tissue and are thus protected also. They provide food for the coral and give it its colour. Environmental stress causes a breakdown of this symbiotic relationship: the corals expel their zooxanthellae, leaving the colourless calcium carbonate skeleton. Stressful conditions are created by higher or lower sea temperatures than the norm; higher or lower light levels (zooxanthellae are photosynthetic); an inundation of fresh water; or pollution. Bleaching tends to occur on specific occasions, known as mass coral bleaching events. AIMS has been studying such events for 30 years: the summer of 1997-98 was one of the hottest last century, and aerial surveys of 650 reefs revealed bleaching in 21 per cent of offshore reefs and 74 per cent of inshore reefs. Another hot one in 2002 brought about just as much bleaching.

Coral can recover from bleaching events, given time, by 'recruiting' coral from neighbouring reefs. Whether or not it can acclimatise to permanently increased water temperatures is another matter. When too many starfish invade, they will eventually die from lack of food, and again the coral may recover. But if invasions occur more frequently than natural cycles, recovery is unlikely. 

And if you add additional pressures into the mix, the odds are against coral's recovery from the losses reported by AIMS last week and, ultimately, the Reef's survival. Ocean acidification research is relatively new, but so far has indicated that, as the warming of the ocean increases carbon dioxide absorption and the water therefore becomes more acidic, the formation of coral by calcification is impeded. The reef grows more slowly and is less robust, which makes it more prone to erosion, such as during storms, the incidence of which will increase in a warmer world. The impact of tourism (more than 800 operators and 1500 vessels according to Science in Public) and commercial fishing is hotly debated, and terrestrial run-off even more so. The cane growers of Northern Queensland claim to have reduced amounts of harmful pesticides and other agricultural residues reaching the ocean, but are pleading for even more Reef Rescue** funding from the Federal government to bring about further practice change. And then there's the dredging of resource-exporting ports and shipping lanes that causes further reductions in water quality.

The loss of coral is not evenly distributed. North of Cooktown and on the outer Reef there's practically no loss, but further south and on the coastal fringes of the mainland, there's practically no coral. The scientists, as usual, state the facts and apportion no blame or responsibility (apart from that of the Federal government). On the ABC's The World Today, in a debate about saving the Great Barrier Reef, Professor Terry Hughes of the ARC Centre of Excellence for Coral Reef Studies at James Cook University was more forthright:

'What we're seeing now for the first time is that the capacity of the Barrier Reef to cope with recurring cycles has been diminished and that reduction in its ability to bounce back is caused by human activity.'

The major Reef issues cannot be resolved overnight, but much more serious debate must begin now. Any decisions should be taken by the Federal government, not the states: the care of a world heritage site and the repercussions of climate change require the implementation of extraordinary legislation at the highest level. The GBR needs help PDQ.

Professor Hughes again:

'At the moment Reef Rescue basically tinkers at the edges. I think we should be asking big questions, questions that are very difficult to answer, and I don't claim to be an expert in many of them, but I think we should be asking whether, for example, we need a sugarcane industry, whether or not we should in the 21st century be contemplating opening new coal mines, whether we need new coal ports. Those are bold questions that need to be asked.'

I can imagine the peaking of eyebrows all over Queensland, if not interstate. These are indeed bold questions. But they are only the first of many.

  
* http://www.pnas.org/content/early/2012/09/25/1208909109
** The Reef Rescue programme is a five-year (2009-13) Federal government investment of $200 million in the improvement of land management practices. $146 million of that is allocated to Water Quality Incentive Grants