[Coral-List] Coral bleaching and light levels

Richard Dunne RichardPDunne at aol.com
Fri Feb 13 12:25:10 EST 2009


It is wrong to state so unequivocally that light is "a secondary 
factor". It can be a primary factor as publications have shown (e.g 
Brown et al - plenty of pubs). It is much more scientific and accurate 
to say that it is an interplay between light and temperature - see the 
diagram and discussion in the Fitt et al. Review in Coral Reefs. 
Sometimes light is more important and sometimes temperature.

It is also incorrect to say that "light levels are basically unchanged". 
Changes in regional meterology occur as a result of climate change which 
can lead to coral reefs being exposed to much higher seasonal irradiance 
which can tip the balance between corals bleaching or not. In addition, 
changes in sea level can be a very important factor, particularly for 
shallow reefs. The underwater light field is a lot more complicated, and 
affected by many physical parameters (e.g., cloud cover, water surface 
roughness, sediment levels, water depth, bottom type, zenith angle of 
the light field, differential spectral attentuation, etc). Your 
statement about surface light going down (evidence?) is far too 
simplistic to be accurate.

I know this is just Coral List but please can we be a bit more scientific.

Richard P Dunne

Thomas Goreau wrote:
>> From: Thomas Goreau <goreau at bestweb.net>
>> Date: February 13, 2009 10:11:18 AM EST
>> To: billraymond10 at yahoo.com
>> Subject: Re: [Coral-List] Coral bleaching and ocean acidification
>> Dear Bill,
>> Absolutely! But it is a secondary factor.
>> 20 years ago I did a bunch of experiments in Jamaica with corals in  
>> tanks at different temperatures and light level combinations.  
>> Bleaching took place only above a certain temperature, but the more  
>> light the faster it happened. Peter Glynn did similar experiments in  
>> Okinawa and reached the same conclusions. The reason I did this was  
>> our field observations in the first Caribbean bleaching event in  
>> 1987, where shaded corals were much less bleached, in fact where  
>> they were shaded by overhangs you could see the shadow, and we've  
>> seen that everywhere in the Indian Ocean and Pacific since too.
>> But the discussion was about bleaching versus acidification, so I  
>> did not get into secondary factors affecting bleaching. And  
>> temperature has been rising worldwide whereas light levels are  
>> basically unchanged because solar radiation variations are so small.  
>> In fact surface light has been going down for decades because of  
>> atmospheric pollution, but now starting to rise slowly as  
>> atmospheric sulfur and nitrogen pollution are controlled.
>> Hans Creek is an interesting area, and you may know that I proposed  
>> it as a coral reef restoration site. I still hope this is possible,  
>> but it really depends on blocking the marina and golf course. Which  
>> I guess is still a pending issue. There is a small chance that I may  
>> get back to BVI later this year.
>> Best wishes,
>> Tom
>> Thomas J. Goreau, PhD
>> President, Global Coral Reef Alliance
>> Coordinator, United Nations Commission on Sustainable Development  
>> Partnership in New Technologies for Small Island Developing States
>> 37 Pleasant Street, Cambridge MA 02139
>> 617-864-4226
>> goreau at bestweb.net
>> http://www.globalcoral.org
>> On Feb 13, 2009, at 9:57 AM, Bill Raymond wrote:
>>> Tom Goreau:
>>> Don't you consider solar intensity a factor in coral bleaching? In  
>>> Tortola I found bleached corals in late October, offshore, but  
>>> mangrove-shaded Siderastreas in warm Hans Creek
>>> were not bleached.
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