Biological indicators are organisms or biological responses used to assess the health of an ecosystem. They can include species like lichens, macroinvertebrates, or fish that are sensitive to environmental changes, such as pollution or habitat destruction. By monitoring these organisms, scientists can gauge the overall condition of their habitats. These indicators provide valuable information about the quality of air, water, and soil. For example, the presence of certain insects can signal clean water, while the absence of amphibians may indicate environmental stress. Using biological indicators helps in conservation efforts and environmental management.