water quality

Alina Szmant aszmant at rsmas.miami.edu
Thu Dec 19 17:24:35 EST 1996

Dear Ms. Vermeer: 

These are not simple questions with simple answers.  There is no ONE 
concentration of any of those variables that consitutes stress.  It takes 
LOADS of chlorophyll to decrease the amount of light available to benthic 
producers such as corals and reef algae, and corals do fine under higher 
chlorophyll conditions (e.g. East coast of Africa during monsoon) and 
actually get covered up by algae during the worst of the monsoon.  If 
nutrient concentrations are elevated occasionally, as happens naturally, the 
reef absorbs the nutrients into their normal trophic dynamics and are the 
better off for it.  It's only when 'elevated' (I cannot provide  absolute 
numbers, but reef water usually in the 10 - 20 uM TN and 0.1-0.5 uM TP) 
concentrations occur much of  the time and the grazers cannot keep up with 
the production, that the reef becomes nutrient stressed [it takes MUCH 
higher concentrations to physiologically stress the corals themselves; it's 
the biological interactions that get upset by elevated nutrients]; the 
problem is compounded if there is harvesting or die-off of grazers (such as 
the Diadema die-off).  In the Caribbean, all the reefs are heavily 
over-fished (estimates of 10-20 % of natural fish densities), so the trophic 
dynamics are very unbalanced. 

Hope this helps.  Please do not be mesmerized by the few investigators that 
are going around preaching for a "threshold" concept.   There are no data to 
support it and many that refute it. 


Alina Szmant 

At 09:48 AM 12/19/96 -0400, you wrote: 
>Can anyone refer me to recent studies which have been conducted which 
>provide indications of what total nitrogen and total phosphorous values in 
>the water column are considered "stressful" to coral reefs, and/or at what 
>level of chlorophyll-a in the water column are coral reefs considered to be 
>Many thanks, 
>Lotus A. Vermeer 
>Bellairs Research Institute 
>St. James, Barbados, West Indies 
Dr. Alina M. Szmant 
Coral Reef Research Group 
University of Miami 
4600 Rickenbacker Cswy. 
Miami FL 33149 

TEL: (305)361-4609 
FAX: (305)361-4600 or 361-4005 

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