Science behind Great Barrier Reef water quality management

Articles from Peter Ridd of James Cook University in newspapers and on blog sites and letters to the editor supporting his position (e.g. Tom Darlington, 9 February 2010 in the Townsville Bulletin) claim there is no scientific evidence agricultural pollution is damaging the Great  Barrier Reef. As well, claims are made that there is a body of research available (specifically from Peter Ridd’s work) that shows that runoff from farming is having no effect (or very little effect) on the Great Barrier Reef (GBR). Neither of these claims is true.

An example of a healthy reef (Princes Charlotte Bay, Far Northern GBR)

An example of a healthy reef (Princes Charlotte Bay, Far Northern GBR)

There is a large body of published results from hundreds of studies  showing that (with just a few of the possible references):

1. Water discharged from rivers to the GBR continues to be of poor quality in many locations. The main source of pollutants is agriculture (cropping and grazing) e.g Packett et al (2009),  Bainbridge et al (2009).

2. Land derived pollutants, including suspended sediments, nutrients and pesticides are present in the GBR at concentrations likely to cause environmental harm e.g. Lewis et al (2009) and  De’ath and Fabricius (in press).

3. Coral cover on the GBR is generally much lower (about 25%) now than 40 years ago (cover about 50%) e.g. Bruno and Selig 2007. Macroalgal cover appears to be greatly increased e.g. De’ath and Fabricius (in press) Wismer et al (2009)

4. This loss in coral cover has been caused by a combination of  factors – poor water quality (see references above), crown of thorns starfish damage also associated with poor water quality (Brodie et al 2005), bleaching associated with climate change, loss of calcification associated with increased carbon dioxide in the surface water (De’ath et al 2008) and some minor damage from fishing activities.

Most of these results up till 2008 are summarised in the following document (click through for a link to the site and pdf download)

On the other hand there are few published results of research showing that agricultural pollution is having no effect on the Great Barrier Reef – none that I can find. What can be found are unsupported (by research results) opinions. Now we all have opinions and I think mine are as good as anybodies but I don’t pass them off as facts when they are not supported by research results.

An example of a degraded macroalgal dominated reef (Russell Island, Wet Tropics, Northern GBR)

I make no statements about the recently introduced Queensland Government legislation or its likely effectiveness, which remain to be tested, but do claim that there is ample well-founded evidence that agricultural pollution of the GBR is occurring, the effects are severe and that management of this pollution is a necessity.

Jon Brodie
Catchment to Reef Research Group
Australian Centre for Tropical Freshwater Research
James Cook University, Townsville.


Bainbridge, Z.T., Brodie, J.E., Faithful, J.W., Sydes, D.A. & *Lewis*, S.E. (2009). Identifying the land-based sources of suspended sediments, nutrients and pesticides discharged to the Great Barrier Reef from the Tully-Murray Basin, Queensland, Australia. Marine and
Freshwater Research, 60, 1081-1090

Brodie, J.E., Fabricius, K., De’ath, G. & Okaji, K. (2005). Are increased nutrient inputs responsible for more outbreaks of crown-of-thorns starfish? An appraisal of the evidence.
Marine Pollution Bulletin, 51:266-278

Bruno JF, Selig ER (2007) Regional Decline of Coral Cover in the Indo-Pacific: Timing, Extent, and Subregional Comparisons. PLoS ONE 2(8): e711

De’ath G. and Fabricius K. in press. Water quality as a regional driver of coral biodiversity
and macroalgae on the Great Barrier Reef. Ecological Applications

De’ath G, Lough JM, Fabricius KE, (2008) Declining Coral Calcification on the Great Barrier Reef, Science, 323, 116-119

Lewis, S.E. Brodie,  J.E. Bainbridge, Z.T. Rohde, K. Davis, A. Masters, B. Maughan, M.
Devlin, M. Mueller, J. Schaffelke, B. ( 2009) Pesticides: A new threat to the Great Barrier Reef. Environmental Pollution 157, 2470-2484

Packett, R. Dougall, C. Rohde, K. Noble, R. 2009. Agricultural lands are hot-spots for annual runoff polluting the southern Great Barrier Reef lagoon. Marine Pollution Bulletin 58, 976-985.

Wismer S, Hoey AS, Bellwood DR (2009) Cross-shelf benthic community structure on the Great Barrier Reef: relationships between macroalgal cover and herbivore biomass. Marine
Ecology Progress Series 376:45-54.

4 thoughts on “Science behind Great Barrier Reef water quality management

  1. Great post Jon, thanks for this. Especially for the references. And perfect timing given my query in my last post about Ridd’s claim that he “was told that the coral was going to die from sediment, and we have proved that is complete rubbish”

  2. Yes, something of a pattern emerges. Somebody with a science qualification, and research experience, unrelated to the issue – ecology of the reef, greenhouse gas effects – becomes a media darling by taking a contrarian position to that of all the scientists who do have qualifications and experience in that field. That contrarian position just happening to suit the interests of agribusiness, coal and other mining companies, energy companies; and to be met with a chorus of approval by neoconservative think tanks, shock jocks, and conservative politicians.

  3. Excellent post Jon. Reading an article based on the evidence behind this issue is far more fulfilling than the usual fact-free nonsense from Peter Ridd and Bob Carter! Thank you very much for your contribution.

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