[Coral-List] de'ath et al on coralscience.org

[Richard Dunne]

Dear Tim and Coral Listers


OCAEN ACIDIFICATION AND SEA TEMPERATURE WARMING - THEIR ROLES IN 
DECREASING CORAL CALCIFICATION

Your website commentary of De’ath et al.’s paper focuses largely on the 
problems of ocean acidification.The authors were MUCH more circumspect, 
since they were unable to ascribe the declining calcification to any 
specific environmental signal (either temperature or seawater acidity). 
This is important because we still need scientific evidence of any 
causative link.

A subsequent study (Tanzil et al. 2009 Coral Reefs – DOI 
10.1007/s00338-008-0457-5) from South Thailand on reefs in warmer waters 
closer to the equator (7 deg N) also demonstrated a similar decline in 
calcification, which like the GBR study was due to decreased linear 
extension and not to any changes in bulk density. Whilst the data 
available to Tanzil et al. for ocean acidification was sparse and 
incomplete, nonetheless no obvious link existed, but the authors were 
able to demonstrate that the decrease in linear extension was associated 
with a significant long term increase in sea temperature (R squared 
between 10 and 30%).

The common finding in both studies, that there was no change in bulk 
density, may also be important, for it implies that whilst these corals 
may be growing less slowly, they are still producing robust skeletons, 
although an earlier study by Cooper et al. (2008 Global Change Biology 
14:529-538) had found a small decrease (6%). As Atkinson & Cuet (2008 
MEPS 373:249–256) point out, we are still a long way from understanding 
how changes in ocean acidity may affect coral calcification, 
particularly in natural conditions. At the moment whilst rising sea 
temperatures clearly seem to be reducing the growth of corals, there is 
still much work to be done to demonstrate whether the same is true for 
changes in ocean acidity.


ABSTRACT OF TANZIL et al.: 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.

Richard Dunne


Tim Wijgerde wrote:
> Dear all,
>
> this afternoon I wrote a little article on the
> publication of De'ath et al, to again point out the negative effects of
> climate change on the Earth's coral reefs. Again, only Mozilla Firefox
> works well with our website.
>
> http://www.coralscience.org/home/content/view/176/1/lang,english/
>
> Best
>
> Tim
> ****************************************
>   
> Tim
> Wijgerde, M.Sc.
> CEO Coral Publications
> www.coralscience.org
> www.koraalwetenschap.nl
> (Mozilla Firefox optimized)
> info at coralscience.org
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