Phosphorus, Nitrogen and Frogs
Watch this video of the study of vernal pools as it ties into a new study from the University of Colorado.
High levels of nutrients used in farming and ranching activities fuel parasite infections that have caused frog deformities in ponds and lakes across North America. The study out of the University of Colorado showed increased levels of nitrogen and phosphorus cause sharp hikes in the abundance and reproduction of a snail species that hosts microscopic parasites known as trematodes.
The nutrients stimulate algae growth, increasing snail populations and the number of infectious parasites released by snails into ponds and lakes. The parasites subsequently form cysts in the developing limbs of tadpoles causing missing limbs, extra limbs and other severe malformations.
The research team built 36 artificial ponds in central Wisconsin similar to farm stock tanks and stocked each with selected numbers of snails and tadpoles of the green frog. In addition to adding nutrients, the researchers took on the role of birds in the trematode life cycle by adding parasite eggs to the tanks, then measuring the subsequent ecological responses.
In ponds with added nutrients, snail biomass increased by 50 percent and the snails increased parasite egg production by up to eight-fold. The infection rate in frogs rose by two- to five-times in those tanks.
As few as 12 trematode larvae, known as cercariae, can kill or deform a single tadpole by burrowing into their limb regions and disrupting normal leg development. A single infected snail can produce more than 1,000 cercariae in one night. Frogs that become deformed rarely survive long in the wild.
A recent study of more than 6,000 species of amphibians worldwide concluded that 32 percent were threatened and 43 percent were declining in population. While the causes range from habitat loss to emerging disease, the researchers are now exploring how nutrient pollution and limb malformations contribute to the pattern.
September 26, 2007 7:08 AM | Category: Animals