1. Lab: Benthic Bugs and Bioassessment
Fun with Macroinvertebrates
Lab: Benthic Bugs
and
Bioassessment

2. What are aquatic macroinvertebrates?
Aquatic means they that live in water (at least part-time)
Macro means they can be seen without the aid of a microscope or other magnifying device
Invertebrates are animals without backbones

3. Why care about aquatic macroinvertebrates?
Macroinverts are valuable indicators of the health of aquatic environments because they are benthic.
Benthic means they are typically found on the bottom of a stream or lake and do not move over large distances
Thus, they cannot easily or quickly move away from pollution or other environmental stresses
So…?

4. So…..
Different macroinvert species react differently to environmental stressors like
Pollution
Sediment loading
Habitat changes
Quantifying the diversity and density of different macroinverts at a given site can create a picture of the environmental conditions of that body of water

5. Intolerant vs. tolerant macroinverts
If exposed to an environmental stressor (pollution, warming due to low flows, low dissolved oxygen due to algal blooms, etc.):
Intolerant macroinverts may die
Tolerant macroinvert species often inhabit spaces vacated by intolerant organisms,
The result is an entirely different population of organisms!

6. Macroinverts in healthy water bodies
A healthy water body will typically contian a majority of intolerant macroinverts such as:
Mayflies (Ephemeroptera)
Stoneflies (Plecoptera)
Caddisflies (Tricoptera)

7. Macroinverts in stressed water ecosystems
A body of water under environmental stress will contain a majority of macroinverts that are tolerant of these conditions, such as:
Leeches (Hirudinea)
Tubifex worms (Tubifex sp.)
Pouch Snails (Gastropoda)

8. Bioassessments of Macroinverts
Help biologists and others trying to help determine the health of a river;
Use inexpensive equipment;
Are scientifically valid when done correctly;
Can be conducted by YOU!
Provide benchmarks to which other waters can be compared;
Can be used to define rehabilitation goals.

9. How do I conduct a Bioassessment?
Collect, identify and quantify macroinverts;
Use simple formulas to calculate relative water quality based on diversity and quantity of sampled organisms
These formulas, called metrics, relate the numerical diversity and density of organisms to a water quality rating

10. Common macroinvert metrics
The most common metrics are :
The EPT/Midge ratio
The Pollution Tolerance Index

11. EPT/Midge Ratio metric
The EPT/Midge Ratio metric compares the total number of intolerant organisms (e.g. the EPTs) with the total number of midges.
Typically the higher the number of intolerant organisms, the better the water quality
Midges are a group that include many kinds of small flies. They are found (seasonally or otherwise) on practically every land area outside permanently arid deserts and the frigid zones. The most common midges inhabit urban areas are known to cause skin irritation and are attracted to plasma screens and other light source. The term "midge" does not define any particular taxonomic group, but includes species in several families of Nematoceran Diptera

12. The Pollution Tolerance Index
The Pollution Tolerance Index assigns a numerical value to each macroinvert order, with higher numbers assigned to pollution-intolerant organisms,
The scores are totaled and compared with a water quality assessment scale to yield a relative water quality rating for the sample

13. How often?
The US EPA recommends macroinvert sampling be conducted in a way that minimizes year-to-year variability.
Biologists sample for a week during the same season(s) each year
Sampling is conducted when sites are easily accessible and number of organisms is high
Springtime when late-stage larvae are present
Late fall when organisms are more mature

14. Macroinvert + Water Quality + Census data = Knowledgeable students
Anything else?
Biassessments are very useful alone, but are most useful when combined with water quality and other habitat assessments (animal/plant census data).
Macroinvert Water Quality Census data =
Knowledgeable students

15. Today’s macroinvert sampling exercise
We are simulating a bioassessment of a stream using ordinary objects to represent macroinvertebrates
There are three stations that have water sampled from different locations: the macroinvert populations will be different, and you will assess the health of the ecosystem.

16. Today’s macroinvert exercise protocol
Using an aquarium net, you will have 20 seconds to collect as many macroinverts (paper clips, beads, etc.) from your “stream” as possible.
Place your macroinvert samples
in a collection bowl
Sort your macroinverts into categories based on the macroinvert ID sheet, and place them into piles on your sorting trays
Tabulate the sorting results onto the data sheets provided and calculate the percent composition of each macroinvert in the stream site

17. Calculate & Compare: Data analysis
Complete the Pollution Tolerance Index to determine a water quality assessment score
Record your results on the front board so that you can compare your results with the other river station data: collaborate with the other scientists in the room!
Speculate about the cause of the quality of your stream. Describe the habitat, possible pollution sources. Answer the Analysis Questions!