What's happening to the frogs? For several years, scientists around the world have been noticing and studying a global decline in amphibians —especially frogs. Numerous possibilities have been suggested, including pollution, disease, and loss of habitat.
Some researchers think it might be a combination of factors.

One of the Bay Biodiversity Leadership Award winners, Karen R. Lips, is studying amphibian decline in Central America. Read an account of her work at the awards' Web site.

What's an “environmental indicator”? Think of a fever. When you’re feeling sick and your parents think you may be running a fever, they can’t actually see the higher-than-normal body temperature. A fever is a sign of something that’s going on inside your body. Maybe it’s a bad cold, or perhaps an ear or throat infection. Your body is fighting the infection, and that raises your temperature. The fever itself is an indicator of your own personal environment. Your parents or the school nurse use a convenient tool (a fever thermometer) to check on that indicator.

Two indicators: Kenneth Morgan, of St. Mary's County, Maryland, has his temperature taken with a thermometer. But his sister, Sarah, uses the tried-and-true method of hand on forehead to make sure. (Fred Powledge)

If the tool shows that your body temperature is above normal, your parents or the school nurse have valuable information. (If the temperature is normal, it might mean that you’re just trying to avoid the mathematics test.) If the indication is that you’re really sick, they may call a doctor. Or they may decide you need bed rest and plenty of fluids. If one of your ears is full of pressure and pain, that may be another indicator of an infection. Doctors use indicators all the time in their efforts to diagnose the causes of problems. So do automobile mechanics and folks who are trying to figure out why their computers are acting weird. Indicators are extremely helpful tools in gathering information that’s otherwise too difficult to collect.

A clue to the big picture.
An environmental indicator is a kind of a small-time clue to what’s going on in the big picture. If we see a certain sort of tree or plant that is growing in a particular environment, we often can draw other conclusions about the environment, such as what the soil, climate, and rainfall are like. A cactus, for example, might be an indication that the climate is dry.

Because Earth’s environment is so complex, we simply don’t have enough money, time, equipment, or trained researchers to check up on the health of every square meter of rain forest, or river, or prairie. So we search for tools that we can use as indicators of the environment’s health or sickness. Many scientists think that nematodes are good candidates for all-purpose indicators.

Robert K. Niles, a researcher at the Natural Resource Ecology Laboratory, is one of those scientists. Niles thinks that nematodes, with their “tremendous diversity and tremendous abundance,” have a special value in measuring ecosystem biodiversity and health. This is because the wormlike creatures exist in close relationship with so many of the other organisms in soil, as well as with the other processes that go on beneath the surface.

For example: A researcher wants to see what effects an agricultural chemical, applied to crops and thus to the soil in which they grow, has on plant growth. The scientist may have a difficult time measuring any direct relationships between one and the other. But nematodes in the soil may be affected by the chemical themselves, and their diversity may affect the health of the plants. Thus the number and health of the nematodes can become ways the researcher can reach his or her conclusions — they can become indicators. And it is fairly easy to collect and measure nematodes, which are small but not too small to be seen under a magnifying glass — much easier than running elaborate laboratory tests to trace chemicals and their affects on soil and roots.

Sentinels of the environment.
Such indicators are sometimes called “sentinel species” because in a way, they stand guard (without knowing it) over a larger environment. Sentinel species and other indicators are in great demand, says Robert Niles, because “these institutions, policymakers, and other audiences want very immediate kinds of answers. In public health, for example, they want to know, ‘Well, if this water course is polluted, is there an organism in that water course where a change in physiology [the functions of organs, cells, and the like] or metabolism [the chemical changes within the cells of a living body] is going to indicate far ahead of time the levels of pollution that are harmful to humans?’ It’s like the canary in the coal mine.”

Miners who dig for coal and other substances in deep-earth tunnels once carried caged canaries with them. Poisonous gases and other “bad air” would strike down the small birds before they would affect the humans, and the miners would be able to flee.

Nowadays, the miners’ canary has been replaced by electronic sensors. But the practice took a new twist in the fall of 2001 when Americans were worried about an outbreak of anthrax, a sometimes deadly bacteria. There were reports that some people were going to pet shops and buying caged birds, guinea pigs, and other small animals on the theory that if anthrax spores invaded their homes or offices, the death of the smaller animals would be a tip-off.