[Coral-List] Cooling reefs to prevent bleaching

Alan E Strong Alan.E.Strong at noaa.gov
Sun Jan 11 09:29:40 EST 2009

Thanks Tom...these are exactly the types of calculations (from physical 
oceanographers) that need to be explored before anyone gets their hopes 
up with an "easy fix" to a bleaching event.


Thomas Goreau said the following on 1/10/2009 2:56 PM:
> Pumping water from below the thermocline to protect corals from  
> bleaching seems to have become something of a fad lately, but this is  
> very easily seen to be untenable. If the temperature differential  
> between surface and deep waters is 10 degrees C, and coral reefs are  
> elevated by 1 degree C above their bleaching thresholds, then one  
> needs to pump enough water to mix at least 10% deep water into surface  
> waters to get temperatures down to safe levels, but it needs to be  
> understood that this implies a very large vertical flux because  
> surface waters are not static, that is to say the water being pumped  
> up must be at least 10% of all horizontal wind, wave, tidal, and  
> current driven transport of surface waters at the site. However, deep  
> waters in the Caribbean contain nutrient concentrations around 30  
> times the eutrophication thresholds for coral reefs, and deep  
> IndoPacific waters about 60 times these levels, so even if there are  
> ZERO nutrients in surface waters (that is, places lacking ANY land  
> based sources of nutrients), then only a 3.3% mixture of deep  
> Caribbean waters or a 1.6% mixture of deep IndoPacific waters would  
> trigger massive benthic algae blooms, and if there are any land based  
> sources of nutrients the mixtures must be considerably smaller.  
> Therefore one can't protect HotSpots from bleaching by artificial  
> upwelling unless you want to smother the corals with weedy algae.  
> These algal blooms are well known to follow cold water upwelling  
> events, and have been especially well documented in reef locations  
> with high upwelling such as the Gulf of Elat/Aqaba, the Arabian Gulf,  
> Houtman Abrolhos, Lord Howe Island, Galapagos, and high algae reefs on  
> remote uninhabited islands across the Central Pacific with very  
> shallow thermoclines.
> 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
>> Message: 1
>> Date: Thu, 08 Jan 2009 12:21:17 -0500
>> From: Mark Eakin <Mark.Eakin at noaa.gov>
>> Subject: Re: [Coral-List] Cooling reefs to prevent bleaching
>> To: Coral Listserver Listserver <coral-list at coral.aoml.noaa.gov>
>> Message-ID: <39AF8056-8651-40A9-9E3A-0C52CEFD0518 at noaa.gov>
>> Content-Type: text/plain;	charset=WINDOWS-1252;	format=flowed;
>> 	delsp=yes
>> James,
>> I suggest you revisit the Muscatine et al. (1991) study and consider
>> the rates of cool water and nutrient delivery and dilution before
>> dismissing ideas such as these.  The waters are unlikely to be more
>> than 10 degrees cooler than the surface waters and considering the
>> potential rates of water deliver, are likely to be diluted by 10:1
>> before reaching the corals.  Even if we assume only 5:1 dilution, and
>> remember that such proposals are for times of severe thermal stress
>> only, this will barely bring the temperatures below the maximum
>> monthly mean temperatures the corals experience as well.  To quote
>> Muscatine et al. (1991): "Above about 16 "C, and up to 28 "C, the
>> response is similar to that of unshocked controls. "  All proposed
>> mechanisms to cool reefal waters that I have seen are unlikely to
>> lower temperatures to much below 28?C and would only maintain the
>> water flow until seasonal change brings the temperatures back below
>> critical levels.  Nutrients and acidification are certainly concerns.
>> (Please note though, that Cox & Ward (2002) increased and maintained
>> ammonium concentrations in microcosms levels exceeding 20X ambient
>> concentrations for a year.)  Potential enrichment and  acidification
>> and their potential impact on the coral-algal symbiosis need to be
>> evaluated.  This is the purpose of feasibility studies that are needed
>> to evaluate potential side effects such as nutrients and acidity
>> during temporary cooling (or shading, etc.) and weigh them against the
>> effects of inaction (bleaching, disease, mortality).  Our current
>> bleaching outlook calls for a high potential of bleaching-level
>> thermal stress in the GBR and nearby regions over the next two  
>> months (http://coralreefwatch.noaa.gov/satellite/bleachingoutlook/index.html
>> ).  Protecting key reefs could be an important way to help corals
>> survive and the hope is that tools and approaches to protect corals in
>> times of high thermal stress will be available in the future.
>> I also do not recall ever putting up a slide that showed acidic
>> conditions being more of a concern on the "coral killing pecking
>> order" than high temperatures and bleaching.  I certainly did not do
>> so in my Ocean Sciences presentation to which you referred.  That talk
>> focused on the extent and magnitude of the bleaching, disease, and
>> mortality caused by thermal stress in the Caribbean in 2005.  It did
>> contain a table from the Kleypas and Eakin (2007 Bulletin of Marine
>> Science 80: 419-436) paper that listed the top threats to coral reefs
>> as determined by a survey of coral reef scientists and managers at the
>> 10th ICRS, which that ranked Climate Change / Bleaching at #9 (higher)
>> and Ocean Acidification at #47 (lower) and discussed the importance of
>> considering the two together based on our Hoegh-Guldberg et al. (2007
>> Science 318:1737-1742) paper.  Bleaching certainly presents a more
>> clear and immediate threat to coral reefs than acidification.
>> However, the latter has the potential of more broad-reaching and long-
>> lasting effects in marine ecosystems than the former, so both must be
>> considered as important reasons why we need to get atmospheric CO2
>> under control.
>> The key point in my original post was that the threat to coral reefs
>> is too great to eliminate potential approaches out of hand without
>> testing and evaluation, whether the approaches be assisted adaptation
>> or local mitigation.  This is the process of science and it should be
>> allowed to run its course.  We are going to need a wide range of tools
>> at our disposal and should test ideas and submit the results to peer
>> review before stating unequivocally that they cannot work or
>> dismissing them as crazy.
>> Cheers,
>> Mark
> _______________________________________________
> Coral-List mailing list
> Coral-List at coral.aoml.noaa.gov
> http://coral.aoml.noaa.gov/mailman/listinfo/coral-list

**** <>< ******* <>< ******* <>< ******* <>< ******* 
Alan E. Strong, Ph.D.
NOAA Coral Reef Watch, Senior Consultant
....with AJH Environmental Services...
National Oceanic and Atmospheric Administration
NOAA Coral Reef Watch Program
  e-mail: Alan.E.Strong at noaa.gov
URL: coralreefwatch.noaa.gov

E/RA31, SSMC1, Room 5305
1335 East West Hwy
Silver Spring, MD 20910-3226
301-713-2857 x108               Fax: 301-713-3136
Cell: 410-490-6602

More information about the Coral-List mailing list