Reefs at Risk--nutrients

Kerry B Clark kclark at
Tue Jun 30 08:51:23 EDT 1998

J. Charles Delbeek wrote:
>I seem to recall reading a recent paper on a study of nutrient levels off
>of Key Largo and lower down in the keys. Although nutrient levels inshore
>were found to be slightly elevated, those on the outer reef tracts were
>found to be quite low. I don't see how you can make the assertion that
>nutrient run-off is causing problems on these outer reefs when the levels
>are so low?

   Use of standing stock (instantaneous measurements) to estimate nutrient
dynamics is a classic problem in ecosystem analysis, because rapid uptake
can lower the standing stock even if input is high. Enzymes involved in
nutrient uptake of tropical algae have a high nutrient binding affinity, so
one should expect _a priori_ that uptake should be very rapid. Turnover
rates of nutrients can also increase without significantly affecting
standing stock.  Thus, one cannot conclude from low "levels" of nutrients
that nutrient runoff is not a factor in algal overgrowth. In combination
with decreased herbivore populations, as noted, even very slight elevations
could lead to overgrowth. If inshore levels are "slightly elevated" then
one must ask what happens to these nutrients. Rapid uptake as these waters
flow over the reefs is a reasonable explanation.
      We also tend to assume that macronutrients are always the limiting
factor, when micronutrients/trace elements can also contribute to algal
blooms.  These are less frequently considered in causes of algal growth.
Trace elements are also components of agricultural runoff and of human
-Kerry Clark

- -
Kerry Bruce Clark, Ph.D.,  F.A.A.A.S.
Professor of Biological Sciences, Assoc. Dept. Head (Graduate Coordinator)
Florida Institute of Technology, Melbourne, FL 32901-6988
Phone 1-407-674-8195
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