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Studies on the Quality of Fresh Waters of Puerto Rico Relative to the Occurrence of Australorbis Glabratus (Say)

In Puerto Rico, Australorbis glabratus occurs throughout the range of pH and temperature found. It occurs in the maximum concentrations of CO₃, HCO₃, Cl, SO₄, Ca and Mg found in fresh waters here. It is generally but not invariably absent from situations normally having less than 150 ppm. dissolved solids. Yet experimentally, the snail can be maintained for at least two weeks in redistilled water. Small amounts (about 0.1 ppm) of copper in distilled water produce distinct, incapacitating distress in the snails within a few hours time. Copper concentrations in natural waters range from 0.000 to 0.330 ppm. Most concentrations of copper greater than 0.020 occur in waters of less than 150 ppm. It is suggested that copper, and perhaps other heavy metals, may be the factors responsible for the absence of this snail in most dilute waters. A large excess of weak acid radicals (CO₃ and HCO₃) over strong acid radicals (Cl and SO₄) is suggested as related to the absence of this snail in flowing waters on limestone.

¹ Field Team from Department of Medical Zoology, Walter Reed Army Institute of Research, Walter Reed Army Medical Center, Washington 12, D. C.