What group is commonly used as bioindicators to assess stream ecosystem health due to their sensitivity to pollution?

• A. Amphibians
• B. Birds
• C. Macroinvertebrates
• D. Mammals

Answer: (C)

Macroinvertebrates are organisms without backbones that live in streams, including aquatic insects like mayflies, stoneflies, and caddisflies, along with snails and worms. They’re excellent bioindicators because they stay in the stream and reflect water quality over time, and they have a range of tolerances to pollutants. In clean, well-oxygenated water, you’ll see a diverse group with several sensitive taxa; as pollution rises and oxygen levels fall, these sensitive groups disappear first while more tolerant species endure. By examining which groups are present and their abundances, scientists can assess overall stream health and catch pollution effects early. They’re also practical to sample, occur in high numbers, and respond on ecological timescales, making them a direct, localized signal of water quality. Other organisms like birds, mammals, or amphibians are less direct indicators of the stream’s current water quality because they move around more and have more complex life histories.