Biologists in Arkansas began reporting dozens of bald eagles with brain lesions over 25 years ago. The disease was soon found in other birds in the southeastern United States and was linked to a new species of cyanobacteria growing on an invasive aquatic weed.
It was Susan Wilde, an aquatic ecologist at the University of Georgia, Athens, that identified the new neurotoxin produced by cyanobacteria, that is harmful to birds, fish, and invertebrates. The toxin contains bromine, which normally is a rare element in lakes and is not commonly found in cyanobacteria. One possible explanation for the presence of bromine in the toxin is that the cyanobacteria produce it from a herbicide that contains bromide, which is used by lake managers to control invasive weeds, in particular, hydrilla.
It has been discovered that the newly identified neurotoxin produced by cyanobacteria is fat-soluble, which is atypical for cyanobacterial toxins. This suggests that the toxin can accumulate in tissues. Fish and birds are exposed to the toxin when they consume the aquatic weed hydrilla, that is coated with the cyanobacteria. The toxin can then move through the food web as predators such as eagles and owls consume prey that has been exposed to the toxin.
Although recently there has been a successful attempt to control the hydrilla by introducing into the lake fish that consume it , both the weed and the cyanobacterium are hardy and will spread to other places, so saving the birds from the neurotoxin will be a challenging and ongoing battle.
Source: science.org