4: Aquatic ecosystems- Index (indicator) species

Indicator (index) Species:

When water becomes polluted, there tends to be a shift from MANY species of moderate population density to a FEW species of high population density.

The decrease in the diversity of species present is the best indicator of pollution

*  What does the presence of invertebrates that only tolerate high levels of oxygen indicate?
* Examples?

 The presence of invertebrates that only tolerate high levels of oxygen indicates good quality of water:

* Mayfly Nymph
* Caddisfly Larva
* Damselfly Nymph

What species are not good indicators?

Species that breathe surface air, such as water boatmen and water Strider, are not necessarily useful as indicators of water quality.

Large numbers of aquatic worms, which tolerate low concentrations of dissolved oxygen, May indicate poor  water quality and organic pollution.

* What else could large numbers of aquatic worms indicate?

The body of water may be warm and slow moving resulting in low levels of D.O.,  thus would not support organisms that require a lot of oxygen.

Large numbers of Midge larvae May indicate poor water quality and organic enrichment.

*  What are some Organics that in enrich?

* Fertilizer run-off
* Untreated sewage
* agriculture effluent

How does organic enrichment cause poor water quality?

Decay of algal blooms by bacteria remove dissolved oxygen .