Canaries in a mine, frogs in a pond
August 9, 2012 —
Years ago, miners entered a mine to work, and sometimes they were accompanied by a canary in a cage. The idea of the canary was that if there was a low oxygen level or hazardous gas present, the canary would show signs of distress before the miners did; this gave the miners time to evacuate. Thankfully, modern innovations like portable gas meters and self-contained breathing apparatus have eliminated the need to sacrifice any more canaries. The job description of a canary, had it been listed by the mining company, would probably read “bio-indicator.”
A plant or animal species can be a bio-indicator if it is affected by changes in its habitat, whether it is climate change, a natural disease outbreak, or chemical pollution. Sometimes, the mere presence or absence of a species in an area is evidence as to its habitat quality. A macro-invertebrate stream survey would be a good example of this. Some species have experienced population declines not explained by habitat loss, predation or similar events. Enter the frog.
Frogs and toads have proved to be unwitting bio-indicators. Because of their moist, permeable skin, they absorb some of the surrounding environment transdermally, or through their skin. Many species of frogs and toads have experienced population declines: the Northern cricket frog in New York, for example, has suffered a major population decline in the last decade. In the case of cricket frogs and certain other observed events, it is still unknown whether the cause of population decline is natural or manmade. This phenomenon needs to be further studied, but if contaminants are an issue, a frog may well be more sensitive than our most sophisticated chemical analysis techniques (a mass spectrometer obtained by the New York State Department of Health during the Love Canal incident was capable of detecting 0.1 ppb (parts per billion) of dioxin and other target compounds monitored).