Indicator Species (SQA National 5 Biology): Revision Note

Indicator species

• Indicator species are species that, by their presence or absence, indicate the levels of pollution present in the environment

Indicator species for water pollution

• Water pollution occurs when, e.g. raw sewage or fertilisers are released into a body of water, such as a stream

  • This causes microorganisms in the water to increase in number

  • As these microorganisms respire they use up the oxygen in the water

• Some invertebrate species, e.g. stonefly larvae and freshwater shrimps, are highly sensitive to the concentration of dissolved oxygen in the water, making them good indicator species for water pollution

  • The presence of stonefly larvae in a stream or river indicates that the water is not polluted

• On the other hand, some other invertebrate species, e.g. mosquito larvae and blood worms, are unaffected by polluted environments

  • The presence of many blood worms in a body of water, especially if stonefly larvae are absent, indicates a high level of water pollution

Indicator species for air pollution

• Lichen can be used as an indicator species for air pollution

• Lichens are highly sensitive to sulfur dioxide concentrations in the environment

  • Sulfur dioxide is one of the air pollutants released from car exhausts and power stations during the combustion of fossil fuels

• The abundance and type of lichen species growing at a particular location can be monitored to determine levels of air pollution, e.g.

  • a high abundance of lichen indicates clean air

  • a high abundance of bushy lichens indicates very clean air

  • a high abundance of crustose lichens in the absence of leafy lichens indicates more polluted air

Флорист, CC BY 4.0, via Wikimedia Commons (opens in a new tab)(opens in a new tab) and Trio3D, CC BY-SA 4.0, via Wikimedia Commons (opens in a new tab)