Tuesday, 28 May 2013

Haven’t Lost Half of the Great Barrier Reef: Part 2, Junk Methodology

by Jennifer Marohasy
HOW could scientists conclude that half of the Great Barrier Reef has been lost in the last 27 years: target coral reefs most affected by cyclones, coral bleaching and crown-of-thorn starfish outbreaks, while ignoring more representative reefs with healthy corals. And I didn’t make that up! It’s documented in a peer-reviewed study by H. Sweatman, S. Delean and C. Syms entitled: ‘Assessing loss of coral cover on Australia’s Great Barrier Reef over two decades, with implications for longer-term trends’ [1].

Indeed the claim that there has been a 50 per cent decline in coral cover at the Great Barrier Reef appears to be largely an artifice of the survey method. In particular, coral reefs most severely affected by bleaching in 1998, and reefs disproportionally affected by crown-of-thorn starfish outbreaks, and also reefs with insufficient time to recover from cyclones in 2009 and 2011 were targeted for repeated sampling, while more representative reefs with healthy corals were ignored.

In part 1 of this series, I reported that the World Heritage Centre will demand action by the Australian Government to spend vast sums of taxpayers’ funds to address this manufactured issue, or have the Great Barrier Reef placed on its World Heritage in Danger List. This demand is a recommendation of the United Nation’s International Union for the Conservation of Nature, UNESCO, in its State of Conservation report prepared for the June meeting of the UNESCO committee [2], which in turn is based upon a report of the environmental lobby groups WWF and the Australian Marine Conservation Society, whose report [3] in turn relies on the claims of a peer reviewed study by Glenn De’ath and co-workers [4].

The paper by De’ath and co-workers published in the US Proceedings of the National Academy of Sciences in 2012 [5] does indeed claim a 50 per cent decline in coral cover based on 27 years of data from the Australian Institute of Marine Sciences (AIMS) Long-Term Monitoring Program.

The scientists suggests 48 per cent of the decline can be attributable to cyclones, 42 per cent to crown-of-thorn predation and 10 per cent to coral bleaching. But remarkably, and at odds with the broad claims in De’ath et al. 2012, there has arguably been no increase in the incidence of cyclones over the same period [5], no evidence for deterioration in water quality at the Great Barrier Reef [6], and no general increase in the incidence of coral bleaching . So, it would seem remarkable that coral cover has declined so dramatically and purportedly from these sources.

De’ath draw their conclusions from modelling based on a study of just 214 reefs chosen from a total of approximately 3,000 reefs. So they sampled approximately 7 per cent of reefs. They do not explain in the paper how the 7 per cent of reefs were chosen, for example, they do not explain whether they randomly choose the reefs that would be studies as one draws numbers in a lottery, or whether particular reefs were selected. They also don’t explain if they continued to sample the same number of reefs over the 27-year period of the survey, or, for example, whether they reduced the number of reefs sampled over this 27-year period, and, for example, only went back to reefs that showed dramatic decline in coral cover.

Of course while scientists claim to be trustworthy, there is reason to be sceptical. As Aynsley Kellow, Professor and Head of the School of Government at the University of Tasmania, explains in his book ‘Science and Public Policy: The Virtuous Corruption of Virtual Environmental Science’ much of modern environmental science has been corrupted by noble causes. These same causes have brought tremendous prestige and wealth to many scientists.

Remarkably many problems with the AIMS long-term monitoring program, the exact same program relied upon by De’ath and co-workers to conclude half of the Great Barrier Reef has been lost, are detailed in a paper published just one year before by Hugh Sweatman and co-workers [1]. Sweatman and De’ath are colleagues at AIMS and incredibaly Sweatman is one of the authors of the 2012 De’ath paper.

In the 2011 paper Dr Sweatman writes with respect to sampling in the central section of the Great Barrier Reef:
“In the early years of the programme, up to 32 reefs spread across the Swains sector were surveyed annually, but only seven reefs in the south of the Swains sector were surveyed regularly 1993–2004. Five of these seven reefs had large and persistent outbreaks of A. planci for most of the survey period, a high incidence of outbreaks that was not representative of reefs across the sector”.

Sweatman et al. 2011 go on to explain that the overall decline, often reported in coral cover for the Great Barrier Reef, is mainly used to due to large losses of coral in six of 29 subregions. This loss is attributed to coral bleaching in 1998 and outbreaks of crown-of-thorns starfish. Otherwise, Sweatman explains that living coral cover increased in one subregion (3%) and 22 subregions (76%) showed no substantial change.

Furthermore, coral reefs in the great majority of subregions showed cycles of decline and recovery over the survey period, but with little synchrony among subregions and no long term decline.
Sweatman and co-workers conclude that much of the apparent long-term decrease in coral cover reported in the scientific literature results from combining data from selective, sparse, small-scale studies before 1986 with data from both small-scale studies and large-scale monitoring surveys after that date.

In other words Sweatman et al. (2011) detail problems with the methodology used by all studies that rely on the AIMS monitoring data. Yet these issues, central to the credibility of the claim that there has been a 50 per cent decline in coral cover, are ignored in De’ath et al. 2012.


This is part two of a new series on the Great Barrier Reef and claims that 50 per cent of it have been lost. Read part 1 here:  http://evacuationgrounds.blogspot.com.au/2013/05/the-great-barrier-reef-have-we-really.html

1. Sweatman, H., S. Delean, C. Syms. 2011. Assessing loss of coral cover on Australia’s Great Barrier Reef over two decades, with implications for longer-term trends. Coral Reefs. 30: 521-531

2. IUCN, 2013, State of State of conservation of World Heritage properties WHC-13/37.COM/7B, accessed at http://whc.unesco.org/archive/2013/whc13-37com-7B-en.pdf

3. WWF AMCS, 2013, Report to the UNESCO WHC accessed at http://awsassets.wwf.org.au/downloads/mo030_fight_for_the_reef_report_to_the_unesco_world_heritage_committee_1feb13.pdf

4. De’ath, G., K. E. Fabricius, H. Sweatman, and M. Puotinen. 2012. The 27–year decline of coral cover on the Great Barrier Reef and its causes. Proceedings of the National Academy of Sciences. 109(44): 17995-17999.
cyclone number
5. Data from the Bureau of Meteorology shows no increase in the number or severity of cyclones impacting Australia or the Great Barrier Reef. Click on the image for a better view…
This is contrary to a claim in the De’ath et al. 2012 paper that “cyclone intensities are increasing with warming ocean temperatures”.

6. While it is generally assumed, and inferred, that water quality at the Great Barrier Reef is deteriorating, these claims are not supported by the hard data as detailed in part 1 of this series… http://evacuationgrounds.blogspot.com.au/2013/05/the-great-barrier-reef-have-we-really.html
For example, chlorophyll monitoring on the Great Barrier Reef shows:
“Results to date show that compared with coastal regions in other parts of the world, chlorophyll a concentrations in the GBR lagoon are generally low. Chlorophyll a concentrations vary across the shelf seasonally and also with latitude. There are also persistent local gradients in chlorophyll a concentration, usually away from the coast. Consistent long-term trends in chlorophyll a concentrations haven’t yet been discerned.”. Download this text from AIMs website on April 4, 2013

Furthermore the De’ath et al. 2012 study states: “The disturbance data for COTS and cyclones show periodic and random fluctuations but no systematic long-term variation over the 27 year observation period.”
This article was first published at jennifiermarohasy blog
Permission for this cross post was given by Jennifer Marohasy 

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