[Rhodes22-list] Expanding Dead Zone in the Gulf of Mexico

[Jim White]

Dave:
   
  To jump in and answer your question (and you probably already know the answer), more than likely there was a red tide in progress at the time you were in Sarasota. The organism responsible for that is a single celled dinoflagellate, oftentimes Gonyaulux sp.or Gymnodinium brevis. These organisms, while normally present in small numbers in most subtropical to tropical seawaters, for some unknown mechanism can over multiply in a given amount of water, thus causing an "overcrowding" condition. The organism itself is not necessarily toxic, but upon reaching a sort of "critical mass" they begin to die off (after using up the available nutrients and oxygen), and as a result, the decomposition of the vast numbers of this organism causes the characteristic "red tide". Additional resultant decompositional gasses  can cause respiratory problems in people with even normal and uncomromised lungs, but to asthmatics, it can be especially dangerous. 
   
  We get red tides here every couple of years and they are a genuine pain, eye irritation, sore throats, coughing....not to mention the stink from fish kills, which result from hypoxia produced by 02 biologic uptake by the organism as well as the decomposition of the vast number of dead organisms, rendering the waters within the "red tide zone" decreased oxygen potential/saturation.
   
  .... and of course the shellfish concentrate large amounts of the decomposing critters, thus rendering them unsafe to eat for quite a while....
   
  As far as I know, we have not proved any correlation between red tides and anthropogenic addition of nitrogen based nutirents in the system. As a grad student, I did some studies on another organism which causes a "brown-tide" condition here in the Lower Laguna Madre but was still unable to qualify ag runoff as the primary cause, although it certainly could've had a cataylitic effect along with temperature, salinity, tidal exchange and other variables. In any event, brown tide doesn't seem to have the same hypoxia producing effects that red tide does.....
   
  The GOM dead zone is another form of hypoxia, and one we don't really fully understand. It's inital location near the Mississippi River outlet leads us to believe that there are natural as well as  anthropogenic causes (at least contributing factors),  but there is ongoing research attempting to quantify these effects.  An underlying, and uncontrollable cause of the GOM dead zone (and there are other dead zones world wide) is the blanketing effect of the fresh/salt water interface, whereby, the fresh water (floating on top of the salt water) inhibits oxygen mixing. Again, this is natural and completely beyond our control as humans. 
   
  Cheers
  jw
    
   
  .

DCLewis1 at aol.com wrote:
  
Luis,

Interesting re the dead zones and that it has mapped into Fla historically. 
I know we've been down there (Fla) when there have been a whole lotta dead 
fish on Sarasota beachs and we were warned not to swim in the water if we had 
asthma (why that would matter I don't know, I try not to breath water when I 
swim, strictly air). I'd be surprised if red tides or dead zones are good 
for tourism - and that spells big bucks for Fla.

It would be interesting to know to what extent La and Ms pollution affects 
Fla via circulation. 

The Chesapeake Bay has had a very similar problem with agricultural runoff. 
Fortunately we have an independent non-profit, The Chesapeake Bay 
Foundation, that appears to be successfully suing local governments to enforce 
compliance. They also work with farmers to find economic ways to minimize watershed 
pollution, and volunteers on the Bay to restock/reseed species such as 
oysters. It might be a good model for what's needed in Fla, Ala, Ms, La, and Tx. 
I know the Chesapeake Bay Foundation works with at least Va, Md, Del, and Pa.

You've got a good little oceanographic research aquarium/institute in 
Sarasoata, as I recall, just up from the Sarasota Sailing Squadron. It would be 
interesting to know how they are involved. They'd be a natural lead 
organization for the State of Fla.

Dave



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