Invertebrate Pollution Tolerance

Warm, nutrient-rich water will affect inverebrate populations

Caged canaries were once taken deep inside coal mines to alert the miners of deadly, odourless gases. If a canary died in its cage, it was time for the miners to quickly evacuate to the surface.

In a similar way, benthic (bottom dwelling) invertebrates can indicate the presence of pollution in a river. Some invertebrates are very sensitive to pollution and quickly die off.

Invertebrates are good "bio-indicators" of pollution for several reasons:

• Invertebrates are basically stationary even though the river is constantly moving past them. The impact of any pollution can be seen in the surviving organisms long after all traces of a chemical have been washed away.

• Invertebrates have a relatively long life cycle of one to three years. They are available to measure pollution over long periods and at low concentrations.

• If scrapers or collectors become more common, they may be an indicators of organic nutrient pollution and increased algae growth.

• If the water quality has been impacted by pollution, it will be home only to those invertebrate species that are tolerant of pollution and these may be present in very great numbers.

It should be noted that surface-breathing invertebrates such as water striders, lunged snails and adult beetles do not depend on dissolved oxygen and therefore have limited use as bio-indicators of pollution. They may be able to live in oxygen poor water by breathing with surface air.

"Chemical measurements are like taking snapshots of the ecosystem, whereas biological measurements are like making a videotape."

- Professor David M. Rosenberg
University of Manitoba