Endangered Species Handbook

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Aquatic Ecosystems

Toxic Chemicals: Page 4

     Within the past decade, sea turtles in Florida Bay and the surrounding waters have shown signs of disease caused by toxic chemicals.  Hundreds of turtles have been found dead or dying, some with massive tumor growths on their skin, covering their heads, necks and legs.  It is thought that these growths are caused by a virus that attacked the turtles because of their lowered immunity system, which was in turn caused by pollution such as runoff from farmland or inadequate food when sea grasses died off.  Some of these turtles have been saved by placing them in aquariums for months to build up their immune systems.  Because of the increasing number of sick turtles seen, however, and the other problems that these sea turtles face, many scientists now believe that within 50 years, sea turtles will have disappeared from Southeastern waters.
     Chemical runoff from agriculture in the reclaimed marshes of central Florida is thought responsible for the outbreaks of red tide organisms that killed hundreds of endangered Florida manatees (Trichechus manatus latirostris) in 1996, devastating their populations.  A total of 415 manatees died that year, a record number.  Of these, a large percentage died from the toxins.  The hundreds of dying manatees, who exhibited no symptoms prior to their deaths, caused great concern among scientists and conservationists who cooperated to discover the cause.  Analyses of tissues carried out by the Florida Marine Research Institute and federal, state and private agencies finally concluded that red tide toxics produced by dinoflagellates were the cause.   Some of the sick Florida manatees exhibited neuromuscular problems consistent with those previously described in manatees exposed to red tides and were taken to a rehabilitation facility at Lowry Park Zoo in Tampa (Turner 1996).  Three females recovered over a period of three days, during which time they required assistance to stay afloat for breathing (Turner 1996).
     Although red tide is a natural phenomenon, scientists believe that these tides, which have been occurring with greater frequency in recent years, are erupting as a result of effluents, such as sewage and agricultural fertilizers and pesticides (Broad 1996).  The average number of Florida manatees that die each year was 100 or fewer prior to 1990, but since then, each year 200 or more die.  The effects of pollutants may be a major factor in the doubling of their death rate at a time when toxic chemicals have become pervasive in Florida waters.  Since a female manatee has only one young every five to seven years, this death rate is far greater than the recruitment rate. 

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