Indicator species and pollutionSpec 9.16B
In short
Indicator species are organisms whose presence or absence gives evidence of the level of pollution in an area. Bloodworms and sludgeworms suggest polluted water, while freshwater shrimps and stonefly nymphs suggest clean water. Lichens and blackspot fungus on roses indicate air quality. They are cheap and easy to use, but less accurate than instruments.
Some species are sensitive to pollution and some tolerate it. The presence or absence of indicator species gives evidence of the level of pollution in an area.
| Pollution | Indicator species | What it shows |
|---|---|---|
| Polluted water | Bloodworms, sludgeworms | These can live in water with very little oxygen, so many of them suggests the water is polluted (for example with sewage) |
| Clean water | Freshwater shrimps, stonefly nymphs | These need water with plenty of dissolved oxygen, so their presence suggests clean water |
| Air quality | Different species of lichen | Lichens differ in how sensitive they are to sulfur dioxide, so the species present indicate the level of air pollution. Few or no lichens suggest poor air quality. |
| Air quality | Blackspot fungus on roses | The fungus is sensitive to sulfur dioxide, so it is more common where the air is cleaner |
Evaluating the use of indicator species
- Advantages: cheap and easy, needs little equipment, and shows the effects of pollution over a period of time, not just at one moment.
- Limitations: gives only a rough idea of pollution level, because other factors such as temperature or habitat may also affect the species present; it does not identify which pollutant is present; and it is less accurate than measuring with instruments such as an oxygen meter or sulfur dioxide meter.
In an evaluation, finish with a judgement. For example: indicator species are useful for a quick survey, but instruments are needed for an accurate measurement.
Written and checked against the Edexcel GCSE Biology (1BI0) specification · Updated October 2026