[Coral-List] Sahara dust, hurrincanes, flooding, fire: when is a disturbance not a disturbance?

[Gert Jan Gast]

Dear all,

It's not only how long dust has come over, but also how much. I'm not familiar with the exact history of the size of the Sahara, but the Romans hunted elephants and lions along the coast of North Afrika. 2000 years ago the Sahara desert was much smaller than today. It's well know that deserts grow and their actually is an international treaty against desertification (the third establish in Rio along with biodiversity and climate change or "Kyoto"). It would be dangerous to suppose that the coral reefs are adapted to the current load of dust aside from the composition as others have pointed out.

Best, GJ

=============================
Dr Gert Jan Gast
Seas and Oceans Campaigner
Greenpeace Netherlands
Jollemanhof 15-17
1019GW Amsterdam
Phone +31 20 5236655
Mobile +31 6 5206 2976
Fax +31 20 6221272

>>> "Felix Martinez" <Felix.Martinez at noaa.gov> 27-7-2005 15:56 >>>
Dear Listers,

The Sahara dust issue brings to mind a lesson from my short stint as a 
headwater stream ecologist.  Although from our perspective it is easy to 
see flooding as a disturbance, stream communities have evolved with 
flooding and have adapted to withstand or rebound from them.  Similarly, 
coral communities have evolved under the onslaught of hurricanes to 
rebuild between hits and fire brings renewal to temperate forests and 
grassland ecosystems

Sahara dust has been blowing over the tropical America long enough for 
communities to evolve with it.  I remember learning that epiphytes in 
the Amazon/Central American/Caribbean forests grow on substrate 
deposited by Sahara dust storms over tree branches and trunk nooks and 
crannies.

Caribbean corals have certainly been exposed over millenia to Sahara 
dust.  What they have not evolved with is the ability to respond to the 
combination stressors brought about human activity from the mid-20th 
century on.  Disruption of fish assemblages (i.e., disappearance of 
predators and most grazers) and increased sediment/nutrient loads have 
created conditions in the Caribbean in which coral communities cannot 
rebound from natural stressors (i.e., hurricanes), the likely case for 
most of the elkhorn coral disappearance.  If we don't work to restore 
(and protect) the coral communities as a whole, we will be hard pressed 
to see any resistance/resilience to natural (i.e., unavoidable) stressors.

It is human nature to seek single culprits.  We need to learn to think 
that events in nature do not occur in isolation and act accordingly.

Felix

-- 
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Felix A. Martinez, Ph.D.
NOAA Oceans and Coasts
Center for Sponsored Coastal Ocean Research
National Centers for Coastal Ocean Science
N/SCI2, SSMC4 Rm. 8083 		ph: 301-713-3338 x153
1305 East-West Hwy.  		fax: 301-713-4044		
Silver Spring, MD 20910  	email: felix.martinez at noaa.gov 

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