Posts Tagged ‘Coral reef’

Young coral reefs will be unaffected by any ocean acidification due to increased carbon dioxide

August 14, 2013

Well now!

File:PH Scale.svg

pH scale : Wikipedia

While I have no belief in the fanciful theory that man-made carbon dioxide emissions will have any significant effect on global warming, I have no doubt that an increasing carbon dioxide concentration in the atmosphere will lower the pH of the ocean (and they will only be more acidic in the sense of reducing alkanity though with a pH remaining well over 7.0). In fact it is likely that oceans will maintain a pH over 8.0 even in the worst scenarios. (Liquid solutions are usually described as acidic with a pH of less than 7.0 and as alkaline with a pH over 7.0 though on the continuous pH scale any reduction of alkanity is per force an increase of acidity and vice versa).

A new paper shows that the hypothesised catastrophic scenarios about ocean “acidification” (more correctly – a reduction of alkanity) and the consequent effects on coral reefs are little more than fantasy because they find that “there will be no direct ecological effects of ocean acidification on the early life-history stages of reef corals, at least in the near future”.

CM Chua, W Leggat, A Moya, AH Baird. Near-future reductions in pH will have no consistent ecological effects on the early life-history stages of reef coralsMarine Ecology Progress Series, 2013; 486: 143 DOI:10.3354/meps10318

Abstract: Until recently, research into the consequences of oceanic uptake of CO2 for corals focused on its effect on physiological processes, in particular, calcification. However, events early in the life history of corals are also likely to be vulnerable to changes in ocean chemistry caused by increases in the atmospheric concentration of CO2 (ocean acidification). We tested the effect of reduced pH on embryonic development, larval survivorship and metamorphosis of 3 common scleractinian corals from the Great Barrier Reef. We used 4 treatment levels of pH, corresponding to the current level of ocean pH and 3 values projected to occur later this century. None of the early life-history stages we studied were consistently affected by reduced pH. Our results suggest that there will be no direct ecological effects of ocean acidification on the early life-history stages of reef corals, at least in the near future.

ScienceDaily:

Corals can survive the early stages of their development even under the tough conditions that rising carbon emissions will impose on them says a new study from the ARC Centre of Excellence for Coral Reef Studies. …. 

Dr Andrew Baird, Principal Research Fellow at the ARC Centre of Excellence for Coral Reef Studies and James Cook University, was part of the research team and explains their findings.

“The prevailing view is that ocean acidification will act like a toxin to corals, but we were unconvinced by results from previous work on young corals and ocean acidification so we tested critical early stages of development in several coral species at several different acid (or ‘pH’) concentrations of seawater.

“Our results showed no clear response to increasing ocean acidification in any of the stages, or for any of the coral species,” says Dr Baird. “In fact, in only one of nine experiments did we get the response expected if CO2 was acting like a toxin. More often than not we found no effect.”

By bubbling CO2 through seawater the research team was able to simulate future levels of ocean acidification expected to result from rising human carbon emissions. They tested the success of embryo development, the survival of coral larvae and finally their success in settling on coral reefs.

The rest of the reporting by ScienceDaily is almost embarassing as they try to pay lip-service to the orthodoxy of the “the carbon dioxide is evil” fantasy. They waste space in trying to emphasise that even if young corals are not affected this “study does not discount the possibility that coral larvae may suffer other ill-effects from increasing ocean acidification, for example, their swimming speeds may slow down, but because coral larvae typically settle on the reef two or three weeks after birth it is unlikely that these effects will have a major impact on the survival or settlement of coral larvae”.

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Coral reef not so sensitive to global warming after all (if it ever was)

April 5, 2013

Another “climate sensitivity” to join the long list of global warming exaggerations. A coral reef has recovered from a severe “bleaching” event in just 12 years to a level that was thought to require many decades. In fact the assumption that the cause of the severe disturbance in in 1998 was due to global warming is itself looking very shaky. After all, if it was due to global warming (rather than some local temperature or other event) then why on earth did it reverse in 1998? Or is it just a coincidence that no global warming has been observed since that time?

Polar bear numbers are increasing, clouds may “cool” more than they “heat”, the earth’s green cover is increasing, the Antarctic has more ice than it ever had and the Arctic ice variability is not unprecedented and glaciers are not melting at any greater rate than the pre-industrial rate. It is becoming increasingly clear that the “sensitivity” of the global climate to carbon dioxide has been grossly exaggerated.

Location of Reef building corals

Location of Reef building corals (Photo credit: Wikipedia)

“Recovery of an isolated coral reef system following severe disturbance”, by J. P. Gilmour, L. D. Smith, A. J. Heyward, A. H. Baird and M. S. Pratchett  published online at Science on Friday, 5th April, 2013.

Abstract: Coral reef recovery from major disturbance is hypothesized to depend on the arrival of propagules from nearby undisturbed reefs. Therefore, reefs isolated by distance or current patterns are thought to be highly vulnerable to catastrophic disturbance. We found that on an isolated reef system in north Western Australia, coral cover increased from 9% to 44% within 12 years of a coral bleaching event, despite a 94% reduction in larval supply for 6 years after the bleaching. The initial increase in coral cover was the result of high rates of growth and survival of remnant colonies, followed by a rapid increase in juvenile recruitment as colonies matured. We show that isolated reefs can recover from major disturbance, and that the benefits of their isolation from chronic anthropogenic pressures can outweigh the costs of limited connectivity.

PhysOrg writes: Scott Reef, a remote coral system in the Indian Ocean, has largely recovered from a catastrophic mass bleaching event in 1998, according to the study published in Science today. The study challenges conventional wisdom that suggested isolated reefs were more vulnerable to disturbance, because they were thought to depend on recolonisation from other reefs. Instead, the scientists found that the isolation of reefs allowed surviving corals to rapidly grow and propagate in the absence of human interference. Australia’s largest oceanic reef system, Scott Reef, is relatively isolated, sitting out in the Indian Ocean some 250 km from the remote coastline of north Western Australia (WA). Prospects for the reef looked gloomy when in 1998 it suffered catastrophic mass bleaching, losing around 80% of its coral cover. The study shows that it took just 12 years to recover. Spanning 15 years, data collected and analysed by the researchers shows how after the 1998 mass bleaching the few remaining corals provided low numbers of recruits (new corals) for Scott Reef. On that basis recovery was projected to take decades, yet within 12 years the cover and diversity of corals had recovered to levels similar to those seen pre-bleaching.


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