Students collecting indicator species

East Branch Perkiomen Creek - June 2001

Certain species of benthic macroinvertebrates indicate different types of water quality. Benthic means bottom-dwelling. Macro means large enough to be seen, and invertebrates are animals without backbones. They are considered indicator species.
These species can "predict" the overall water quality in a given area. Concentrations of pollutants, temperature and oxygen level can all be determined based on the presence or absence of certain species. Benthic macro-invertebrates include aquatic insects, mollusks, crustaceans, and worms. They can be classified into three main groups based on their tolerance to pollution and oxygen levels

 Sensitive Indicator Species

 Moderately Sensitive Indicator Species

 Tolerant Indicator Species


Macro-invertebrates are good indicators for many reasons.

-They are sensitive to both physical and chemical changes in their environment.

-It is easy to collect and classify them.

-There is a diversity of species included in this group.

-They can't easily leave polluted water.