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.
Sincerely,
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
>"stressed"?
>
>Many thanks,
>
>Lotus A. Vermeer
>Bellairs Research Institute
>St. James, Barbados, West Indies
>
>
>
**********************************************
Dr. Alina M. Szmant
Coral Reef Research Group
RSMAS-MBF
University of Miami
4600 Rickenbacker Cswy.
Miami FL 33149
TEL: (305)361-4609
FAX: (305)361-4600 or 361-4005
E-mail: ASZMANT at RSMAS.MIAMI.EDU
**********************************************
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