[Coral-List] Excess algal symbionts increase coral susceptibility to bleaching

Christina Kellogg ckellogg at usgs.gov
Tue Nov 20 08:21:23 EST 2012

*Yes, African dust has been falling the Caribbean for a long time.

*But only in recent decades would that dust contain a mixture of chemical
nasties (technical term) from the burning of plastic trash, tires, etc.,
plus an increased microbial load from population centers with sewage

*I.e., not just about quantity, but also quality.

*Not to say that dust alone is the cause of everything, but shouldn't be
discounted as a compounding factor on top of our other favorite
environmental insults.


On 11/19/12 6:55 PM, "Douglas Fenner" <douglasfennertassi at gmail.com> wrote:

> *The spatial pattern of bleaching does not correspond well with the pattern
> of dust.
> *African dust fell in the Caribbean long before reefs there started to
> decline.
> Although the Caribbean receives significant inputs of African Dust, the
> Pacific does not.  There was significant bleaching in the Pacific in 1998
> in several places, I know that Palau was hit fairly hard.  The worst
> bleaching in 1998 was in the Indian Ocean.  The northern Indian Ocean does
> get desert dust at times, as shown in the map that Gene pointed to (a
> fabulous map which someone else told me about and I passed on).  But the
> map does not show dust over most of the Indian Ocean, and there was massive
> bleaching south of the dust area.  Thus, the pattern of bleaching in 1998
> does not closely match that of the dust.  The main caveat to that is that I
> don't know when the data for the map was taken.  It looks to me like a
> snapshot, since it shows individual storms.  But I don't know when it was
> based on, and with time these things can change greatly (though the pattern
> is likely to change relatively little).  The main desert areas are north of
> the Indian Ocean, so it doesn't make sense that the middle and southern
> Indian Ocean would get dust.  But the Pacific Ocean can have bleaching in
> spite of very little dust.  Here in American Samoa, the NOAA weather
> station on the windward side of the island measures some of the purest air
> anywhere on earth, since there are many thousands of miles of ocean in all
> directions, particularly east of us where the air usually comes from.  And
> yet bleaching events have occurred here.  Mass bleaching corresponds most
> closely with temperatures, and bleaching events can be predicted quite well
> based on temperatures alone, including in areas without any dust.  Other
> variables can have effects as well, for example the first mass bleaching
> event reported was from fresh water, if I remember (in Jamaica reported by
> Tom Goreau senior).
>      Isn't it the case that African dust has been falling in the Caribbean
> for a very long time, at least 10's of thousands of years?   I believe
> there are layers of it in places like the Bahamas that are very old,
> deposited long before the current decline of the coral reefs began.
>     Cheers,  Doug
> On Fri, Nov 16, 2012 at 11:34 AM, Eugene Shinn <eshinn at marine.usf.edu>wrote:
>> Andrew, This is very interesting information especially because
>> you're findings relate the combined effects of temperature, oxygen,
>> and nutrients to bleaching.  We certainly have all three, including
>> anthropogenic nutrient sources, in Florida but I keep remembering the
>> sudden die-off of Acroporids at San Salvador in 1983. That was a time
>> when there were few anthropogenic sources on that sparsely populated
>> island surrounded by deep oceanic water. John Martins original
>> discovery that iron was necessary for algal growth has been re
>> confirmed by many experiments since then. Because 1983 and 1984 were
>> peak years for African dust flux to the Caribbean I continue to
>> wonder if it contained sufficient iron (also phosphate) to provide
>> this necessary micro nutrient? It is certainly the source of the red
>> soil on that otherwise limestone island. Could the 5-6 percent iron
>> contained in African dust be sufficient to cause overstimulation of
>> both cyanobacteria and dynoflagelate zooxanthellae and thus cause
>> their expulsion i.e. bleaching?
>>        Considering the co incidence of bleaching events with years of
>> increased dust flux and warm quiescent summers makes one wonder. The
>> year 1998 was especially warm and dust flux as measured at Barbados
>> by Joe Prospero was almost as high as it was in 1983 and 1984. With
>> such obvious correlations one would think that some curious coral
>> biologist would have performed dosing experiments to validate or
>> discard the dust hypothesis. Gene  PS: here is a great image of the
>> dust belt provided by Douglas Fenner.
>> <http://www.nasa.gov/multimedia/imagegallery/image_feature_2393.html>
>> --
>> No Rocks, No Water, No Ecosystem (EAS)
>> ------------------------------------ -----------------------------------
>> E. A. Shinn, Courtesy Professor
>> University of South Florida
>> College of Marine Science Room 221A
>> 140 Seventh Avenue South
>> St. Petersburg, FL 33701
>> <eshinn at marine.usf.edu>
>> Tel 727 553-1158----------------------------------
>> -----------------------------------
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