Global Warming Unlikely Reason for Slow Coral Growth
Posted by jennifer, January 4th, 2009 - under News, Opinion.
Tags: Coral Reefs
“Researchers in Australia say the growth of coral on the country’s iconic Great Barrier Reef (GBR) has fallen since 1990 to its lowest rate in 400 years,” variations of this message have been repeated around the world from South Korea to London with global warming, and the associated acidification of oceans, claimed to be the cause.
These reports are repeating claims in an Australian Institute of Marine Science (AIMS) media release made just last Friday to coincide with the publication of research findings in the journal Science [1].
The media release also claimed the research to be “the most comprehensive study to date on calcification rates of GBR corals”.
Having followed GBR issues for many years I was surprised to hear global warming associated with slow coral growth rates, indeed AIMS’s researchers Janice Lough and David Barnes have published detailed studies concluding that coral growth rates increase significantly with an increase in annual average sea surface temperature [2]. Furthermore growth rates actually decrease from north to south along the GBR as this corresponds with a cooling temperature gradient of 2-3 degrees C.
If there has been a slowing in growth rates of coral over the last nearly 20 years, as suggested by this new research, a most obvious question for me would be: Have GBR waters cooled?
This new research paper in Science presents evidence for a decline in coral growth rates since 1990, but no credible reason for the decline. While the study hints that the cause could be ocean acidification no direct evidence is provided to support this claim – not even a correlation. Indeed no data is presented to suggest the PH (a measure of acidity) of GBR waters has changed, and based on modelling of hypothetical changes in PH associated with increases in atmospheric carbon dioxide there is a timing problem – the decline in calcification rates should apparently have started years earlier.
Confronted with a lack of evidence in support of this hypothesis – that ocean acidification has caused the drop in growth rates – the researchers suggest in the paper “synergistic effects of several forms of environmental stress” and implicate higher temperatures. But no data is presented in the paper to contradict the well established relationship between increasing temperature and increasing growth rates – though various confusing statements are made and it is suggested that global warming has increased the incidence of heat stress in turn reducing growth rates – while at the same time the researchers acknowledge higher growth rates in northern, warmer, GBR waters.
Marine Biologist Walter Starck has perhaps aptly described the research as part of “the proliferation of subprime research presenting low value findings as policy grade evidence” and has suggested this has “science headed in the same direction as Wall Street.”
Interestingly, Queensland Premier, Anna Bligh, has decided the “massive decline in the reef’s growth” will require new laws.
None of this, however, gets us any closer to understanding why there has been an apparent dramatic decline in the growth rates of GBR corals over the last 20 years.
*********************
Notes
[1] G. De’ath, J.M. Lough and K. Fabricius (2009) Declining Coral Calcification on the Great Barrier Reef. Science. Volumne 323, pages 116-119
[2] J.M. Lough and D. J. Barnes (1999) Environmental controls on growth of the massive coral Porites. Journal of Experimental Marine Biology and Ecology. Volume 245, Issue 2, pages 225-243
Picture from Walter Starck’s collection.
Re: Comment from: Thomas Moore January 5th, 2009 at 4:51 am
“Can you suggest any other credible alternatives as to why calcification has decreased over the last 20years?”
My resident marine biologist tells me that corals fix their CaCO3 direct from seawater. If, as other people have pointed out, this is not overly dependent on the pH then something else is reducing growth. Well, the polyps certainly aren’t waving their tentacles just for fun: growth rates must depend to a certain extent on captured prey.
One of my explanations for the C12/C13 ‘anthropogenic signal’ in the atmosphere involves changes in oceanic silica levels — more silica, more diatoms, more pull down of heavy C compared with the usual rate because phytoplankton discriminate more against the heavy isotopes than diatoms do.
Farming increases atmospheric dust and mineral run-off in the rivers is very visible as you fly into and out of Cairns. More dust, more silica in the ocean. Diatoms, which bloom earlier than phytoplankton, are limited by silica availability. More dust, more run-off, more diatoms and fewer phytos.
Has the ratio of diatoms to phytoplankton changed? Is the dissolved silica level higher that historical levels? Do corals utilise calcium from their prey? Does a diatom diet provide them with the right mix of nutrients?
So, in answer to your question, no, but I can easily suggest several lines of inquiry. The answer to the whole GW crisis is not spouting, as many do, the mantra ‘there is a consensus, the science is settled’, it’s demanding better science funding and asking _more_ questions. Too few people act as research gatekeepers in the current state of climate research: the money needs to spread more widely and with enough generosity to invoke serendipity. Good science will then triumph over hype and misinformation.
One of the greatest experiences of my life was diving on the GBR. If anyone with millions to spare (oil companies, governments, Mr Gore, I’m not fussy) wants me to sacrifice a few months each year* to directing research efforts then I’d be happy to set up a small team in Cairns. (Thinking about it, I have immediate access to a PhD in phytoplankton carbon fixation, two scuba divers, two marine biologist BScs, an accountant to keep an eye on the money and that’s just in the family. I could do the cooking and drive the boat. Make that ‘I’d be more than happy…’)
JF
Thank you, Australia, for your GBR conservation efforts. I waited 50 years to see it and it was worth the wait.
*Wet fog outside, 0.5 deg C.
Julian – the inner reef lagoon is often subject to exposure of sediment from extensive grazing catchments (water erosion not wind) and nutrients and herbicides from sugar cane lands. 5-10 fold increase of sediment from pre-European http://www.nature.com/nature/journal/v421/n6924/full/nature01361.html
So explanations for decline in calcification could be (a) temperatures (b) CO2 (c) water quality or some combination of all 3.
However, water quality issues have been around for many decades. The effect reported is quite recent. Post 1990.
Why not ask AIMS what work on diatoms/phytoplankton has been done. Might be looked at already.
However insinuating that water quality is a factor also won’t win you any friends on this blog.
But I do like your proposed research project :-)
Is Luke associated with AIMS? What a child.
Tim Curtin:
To answer your query, let’s go back to the De’ath et al article. First the title: “Declining Coral Calcification on the Great Barrier Reef”. That seems to imply that the absolute extent of the GBR is “declining”, and some media have understood that to be the message of the paper. However the text clarifies that declining “calcification RATES” (in grams per square centimetre p.a.) are what the paper seeks to establish.
Thus on page 117 we are told that the “rate of calcification has declined since 1990 “from 1.76 to 1.51 g/cm2/p.a.”, but we are not told what percentage 1.75 g/cm2 is of the average structure of the samples in question. If that was 1000 g/cm2, the decline seems marginal, or even if 100 g/mc2, still not huge, from growth in that case from 1.76% pa to 1.51%. But if language counts for anything at Science it is clear that calcification at the GBR is still growing, albeit somewhat more slowly, with growth having fallen by 0.25 g/cm2/pa, or 14.2%, between 1990 and 2005.
Apparently the rate of decline (i.e. second derivative) increased from 0.3% pa to 1.5% in 2005 but as we are not told what the historic growth rate is – is it 10% pa or 20%? – how do we know whether a 1.5% decline in that rate is big or small? For example, if the historic growth rate was 10% pa. then a decline of 1.5% in that rate reduces it to 9.85%, hardly exciting enough for the hysterical media releases that heralded the De’ath paper.
Can you explain the second derivative like I asked above?
Moreover as is predictable for this kind of paper, it uses 1990 as start year, but that was a cool high growth La Nina year, while its end year 2005 was a hot low growth El Nino, but then why one would expect De’ath & co and their Institute to have heard of ENSO and its impact on climate at the GBR?
It doesn’t use 1990 as the start year.
At least Science’s Elizabeth Pennisi in her Comment on the De’ath paper noted the finding by Alina Szmant at UNC Wilmington “that it’s not clear that carbon dioxide enrichment will have negative effects on calcification rates”, or that either “lower pH or lower CaCo3 [resulting from acidification] will reduce calcification”. I noted before here that De’ath & co scarcely mention the carbonate involved in coral formation, as their stress on calcification implies that calcium is the only coral building block, until their final page, and then they state that with declining calcification “maintenance of the calcium carbonate structure that is the foundation of the GBR will be severely compromised”.
You haven’t uncovered a conspiracy here, Tim. It’s obvious to anyone reading the paper that carbonate is involved in coral calcification. This was never questioned.
Has there been a decline in marine calcium available for formation of aragonate (i.e. CaCo3)? No answer from De’ath. Clearly if he et al. are right, there is no shortage of CO2 to help produce the CaCo3. As Jen notes, the paper even admits growth rates seem higher in the hotter northern section of the GBR than in the colder southern stretches.
What on earth is marine calcium?! Why on earth would there be a shortage of CO2?
The paper clearly discusses temperature thresholds.
No answer from De’ath? Have you emailed him?
Until AGW took over Science, it used to involve precise terminology and measurement. Both are absent from the De’ath paper (and from its so-called “Supporting Material”, which provides no data at all, not even on the alleged declining pH at the GBR for which it provides no shred of evidence even though it is touted upfront as the “cause” of the “declining calcification”).
No shred? At all? So this is one giant conspiracy?
Tim Curtin,
since my last I have discovered a new hoaxer, this time up at AIMS, none other than Janice Lough.
This highlights your misunderstanding of the science, rather than your ability to ‘discover a new hoaxer’.
In her piece with Barnes (2000) she announced that calcification on the GBR is enhanced by rising SST in response to global climate change (p.226, JEMBE);
Lough & Barnes (2000) data set = 1979-1986
in her joint effort with De’ath (Science, 2008)she finds the opposite,
De’ath et al (2008) data set = 1900 – 2005.
The decline occurred after 1990, therefore there is no contrast in the two data sets.
It’s really not that difficult to understand if you read the methods, Tim.
in her solo egffort for JEM 2008, she looks forward to a world “of low coral cover” as “one of the most profound consequences of [you guessed it] global climate change”.
Right.
As it happens i have had early sight of her next paper for these journals, “Global cooling threatens survival of GBR”. I also have it on good authority that the Rudd-Wong team is developing an audacious plan to put the GBR onto floats that will enable it to be towed north to the equator or south to the Antarctic depending on Janice’s current prediction, and thereby provide countless jobs not only at AIMS but for all other equally unemployable in the real world Queenslanders. Are you Luke available to serve as consultant? Contact DCC.
Have you emailed De’ath yet? I’m looking forward to you exposing this ‘hoax’.
Thomas
Julian,
“Can you suggest any other credible alternatives as to why calcification has decreased over the last 20years?”
My resident marine biologist tells me that corals fix their CaCO3 direct from seawater. If, as other people have pointed out, this is not overly dependent on the pH then something else is reducing growth.
Your initial assumptions are wrong – calcification is entirely dependent on pH.
Well, the polyps certainly aren’t waving their tentacles just for fun: growth rates must depend to a certain extent on captured prey.
Corals are indeed heterotrophic, but most corals are predominantly phototrophic (with exceptions)
One of my explanations for the C12/C13 ‘anthropogenic signal’ in the atmosphere involves changes in oceanic silica levels — more silica, more diatoms, more pull down of heavy C compared with the usual rate because phytoplankton discriminate more against the heavy isotopes than diatoms do.
Wait, you’ve lost me here. How does this relate to the De’ath paper? Are you saying corals are declining in calcification because there are less diatoms? Seriously?
Farming increases atmospheric dust and mineral run-off in the rivers is very visible as you fly into and out of Cairns. More dust, more silica in the ocean. Diatoms, which bloom earlier than phytoplankton, are limited by silica availability. More dust, more run-off, more diatoms and fewer phytos.
I think you are misunderstanding this – being autotrophs, diatoms are one of the most common types of phytoplankton.
Besides which, along with the dust is large quantities of nutrients. How is this included in your theory?
Has the ratio of diatoms to phytoplankton changed? Is the dissolved silica level higher that historical levels? Do corals utilise calcium from their prey? Does a diatom diet provide them with the right mix of nutrients?
Again, diatoms ARE phytoplankton.
Corals do not utilise calcium from their prey.
As for a ‘diatom diet’ – corals are predominantly phototrophic, and thrive in oligotrophic waters.
So, in answer to your question, no, but I can easily suggest several lines of inquiry. The answer to the whole GW crisis is not spouting, as many do, the mantra ‘there is a consensus, the science is settled’, it’s demanding better science funding and asking _more_ questions.
I couldn’t agree more. However, none of the lines of inquiry you followed above actually make sense.
Too few people act as research gatekeepers in the current state of climate research: the money needs to spread more widely and with enough generosity to invoke serendipity. Good science will then triumph over hype and misinformation.
As I stated before, nobody has provided any (credible) alternative explanations.
One of the greatest experiences of my life was diving on the GBR. If anyone with millions to spare (oil companies, governments, Mr Gore, I’m not fussy) wants me to sacrifice a few months each year* to directing research efforts then I’d be happy to set up a small team in Cairns. (Thinking about it, I have immediate access to a PhD in phytoplankton carbon fixation, two scuba divers, two marine biologist BScs, an accountant to keep an eye on the money and that’s just in the family. I could do the cooking and drive the boat. Make that ‘I’d be more than happy…’)
You have a PhD in phytoplankton carbon fixation? On what grounds you delineating diatoms and phytoplankton?
*Wet fog outside, 0.5 deg C.
Winter?
Thomas
Rod,
Luke is providing answers, and you call him a child?
Thomas
Tim,
The long core data from the De’ath paper is lodged at:
http://www.ncdc.noaa.gov/paleo/
Put your money where your mouth is, and go show us exactly how De’ath et al are wrong.
Thomas.
Julian,
http://www.floodsclimbers.co.uk/globalwarming.html
Just wanted to add that the Plankton / DMS discussion was pretty intriguing.
Thomas
Still convinced that global warming is an unlikely reason for slow coral growth? A recent paper published in coral reefs suggests that this decline isn’t limited to the GBR:
Tanzil et al. 2009 Coral Reefs – DOI 10.1007/s00338-008-0457-5
“Decline in skeletal growth of the coral Porites lutea from the Andaman Sea, South Thailand between 1984 and 2005″
Of the few studies that have examined in situ coral growth responses to recent climate change, none have done so in equatorial waters subject to relatively high sea temperatures (annual mean >27degC). This study compared the growth rate of Porites lutea from eight sites at Phuket, South Thailand between two time periods (December 1984–November 1986 and December 2003–November 2005). There was a significant decrease in coral calcification (23.5%) and linear extension rates (19.4–23.4%) between the two sampling periods at a number of sites, while skeletal bulk density remained unchanged. Over the last 46 years, sea temperatures (SST) in the area have risen at a rate of 0.161degC per decade (current seasonal temperature range 28–30degC) and regression analysis of coral growth data is consistent with a link between rising temperature and reduced linear extension in the order of 46– 56% for every 1 degC rise in SST. The apparent sensitivity of linear extension in P. lutea to increased SST suggests that corals in this part of the Andaman Sea may already be subjected to temperatures beyond their thermal optimum for skeletal growth.
http://www.springerlink.com/content/c3plnq6522742616/
Thomas. Thanks for the link. However this is what I received when attempting to open each locality on the De’ath listing: Internet Explorer cannot display the webpage.
However I was able to open the plots for calcification etc, and found for the first (Darnley) and last (Masthead) that neither went beyond 1990. Obviously it is not possible to analyse the plots unless one has the raw data, which is what you promised I would find. I have noticed before that Science et al consider plots to be data but that is not the case.
Strange that the SI and data archive for a paper claiming to show declining trends since 1990 offers plots that end in 1990. It is however apparent from the plots that there are no obvious trends in any direction. So the ball is in your court. If you can locate the data, perhaps you could send it to me direct please.
Regards
Tim
Tim,
Coral index (http://www.ncdc.noaa.gov/paleo/indexcoral.html)
Multi-site – Density, Extension, and Calcification Data (http://www.ncdc.noaa.gov/paleo/metadata/noaa-coral-1863.html)
Try using something other than Internet Explorer. Firefox is good. Let me know if you are still having problems.
Thomas
Thomas> Thanks, but neither of your links works for me. What is Firefox? If that works for you, could you just download the data into Excel, and forward to me? My email address is readily available from Jen or my own website:
http://www.timcurtin.com
Regards
Tim
Thomas: Jen’s last was a timely post, at least for me, as I have just finished analyzing the De’ath data at NOAA to which I was helpfully linked by you. As you will recall, De’ath & co claimed to have evidence showing declining calcification rates at the GBR between 1990 and 2000/2001.
I was eventually able to open the De’ath archive at NOAA, to find that of their 14 cores/samples, no fewer than 9 exhibited INCREASING calcification rates from 1990-2000/2001, pace their media release and assertions in their Science article. The density trends on their data are mostly flat.
I fear that De’ath and Lough, et al. are merely (like most “scientists” these days) just a variant of the Bernie I “Madoff with our money” school, given that they are all funded by half-witted Ponzi taxpayers like you-me. The sooner AIMS at Townsville is shut down the better for all of us. The Media Release on their “discovery” is a travesty, like the rest of their work. What is it that impels no doubt well-meaning scientists to sell their souls to the devil, again and again? One supposes that De’ath et al are reasonable human beings like the rest of us, but that they cannot bring themselves to submit their work to a half-intelligent statistician to check their findings?
For the record, of the 14 GBR sites they report, only THREE do not yield increasing calcification rates, this in a paper trumpeted around the world as showing that “climate change” would bring about the collapse of the GBR sooner rather than later.
Tim,
Thomas: Jen’s last was a timely post, at least for me, as I have just finished analyzing the De’ath data at NOAA to which I was helpfully linked by you. As you will recall, De’ath & co claimed to have evidence showing declining calcification rates at the GBR between 1990 and 2000/2001.
I was eventually able to open the De’ath archive at NOAA, to find that of their 14 cores/samples, no fewer than 9 exhibited INCREASING calcification rates from 1990-2000/2001, pace their media release and assertions in their Science article. The density trends on their data are mostly flat.
I fear that De’ath and Lough, et al. are merely (like most “scientists” these days) just a variant of the Bernie I “Madoff with our money” school, given that they are all funded by half-witted Ponzi taxpayers like you-me. The sooner AIMS at Townsville is shut down the better for all of us. The Media Release on their “discovery” is a travesty, like the rest of their work. What is it that impels no doubt well-meaning scientists to sell their souls to the devil, again and again? One supposes that De’ath et al are reasonable human beings like the rest of us, but that they cannot bring themselves to submit their work to a half-intelligent statistician to check their findings?
For the record, of the 14 GBR sites they report, only THREE do not yield increasing calcification rates, this in a paper trumpeted around the world as showing that “climate change” would bring about the collapse of the GBR sooner rather than later.
It seems that empty vessels make the most sound. Please, show us your analysis.
Thomas
[...] http://jennifermarohasy.com/blog/2009/01/global-warming-unlikely-reason-for-slow-coral-growth/?cp=al... [...]
[...] 1. Global Warming Unlikely Reason for Slow Coral Growth, by Jennifer Marohasy, January 4th, 2009 http://jennifermarohasy.com/blog/2009/01/global-warming-unlikely-reason-for-slow-coral-growth/ [...]