Bioindicators are living organisms, or groups of organisms, that serve as a natural gauge for the health and quality of an ecosystem. Because they are sensitive to changes in their environment, their presence, absence, or condition can reveal the effects of pollutants or other stressors. By monitoring bioindicators, scientists can assess environmental changes, often more cost-effectively than with purely technical measurements.
The concept of using living organisms to assess environmental conditions has been practiced informally for centuries. However, its formal scientific application began in the early 20th century, particularly in relation to water pollution. Scientists observed that the decline of certain fish species and the proliferation of others correlated with levels of sewage and industrial waste. This led to the development of systematic methods for using species as indicators of ecosystem health.
The use of bioindicators is widespread in modern environmental science. A classic example is the use of lichens, which are highly sensitive to sulfur dioxide, as indicators of air quality. In aquatic ecosystems, the diversity of macroinvertebrates (like mayflies and stoneflies) is a key indicator of water purity. Frogs and other amphibians, with their permeable skin, are excellent indicators of both water and air pollution. Bioindicators are crucial tools for conservation, environmental management, and providing early warnings of ecological damage.