Aquatic Invertebrates
Aquatic macroinvertebrates are invertebrates that can be seen with the naked eye. They include many larvae of insects such as mosquitoes, dragonflies and caddis flies that begin their lives in the water then metamorphose into adult forms that live on land. Beetles, crustaceans, snails, worms and leeches are other examples of aquatic macroinvertebrates. These creatures can populate ponds or streams in amazing numbers – some up to thousands in a square meter. They are an important part of the food chain. Macroinvertebrates can tell us a lot about the conditions within a water body. Many macroinvertebrates are sensitive to changes in pH, dissolved oxygen, temperature, salinity, turbidity and other changes in their habitat. Habitat includes food resources and the physical characteristics of the environment such as places and materials to build nests, raise young and keep them safe from predators. Rocks, sticks, dead and decaying vegetation and other living organisms such as plants provide key habitat for aquatic macroinvertebrates..
To monitor Freshwater Macroinvertebrates, we want to estimate biodiversity, examine the ecology of the water body and explore relationships among water chemistry measurements and organisms. Most often it is impossible to count all individuals of every species present in a habitat, so we take samples of organisms from the habitat, and calculate the diversity found in these samples to estimate the biodiversity of the habitat. Biodiversity is the number of different kinds of organisms in an ecosystem and the population of that species. Biodiversity may be estimated from species data, or from broader categories like the number of different kinds of arthropods. Scientists often use metrics to learn about the ecology of the water body. Metrics are derived from counts of organisms in samples at a variety of sites. A simple metric is the number of organisms. Organisms can also be put into groups such as the percentages of organisms using specific feeding strategies (grazers, filter feeders, and predators), or percentages of long-lived and short-lived taxa.
Taking chemical measurements in a water body is like looking at a picture of what is going on in the water at that time. Taking biological measurements is like watching a movie of things that happened over time in the water in a single visit. Macroinvertebrates record the history of a water body because many are sessile (stay within a small area) and live one or more years while the water flows by. Changes in the habitats (including water chemistry) most likely will cause changes in the macroinvertebrate assemblage.
Using macroinvertebrates to indicate how stressed the water body is:
Scientists studying ecological systems are often interested in what happens to organisms exposed to stress. Stresses can be caused by natural events or human activities. An example of a natural stress in an aquatic system is a major storm that causes extensive flooding. Many macroinvertebrates may die or be washed away. The flooding may cause mud to be deposited in areas that were mainly gravel. This will cause a change in the types of macroinvertebrates that can live there. Macroinvertebrate metrics are often designed and used to examine the types of stresses affecting water bodies by the way macroinvertebrate communities respond to conditions affecting their habitats. By examining data on abundance of different taxa in respect to the macroinvertebrate characteristics such as ecological roles of these taxa in the ecosystem and their tolerance to stress, one can learn much about the aquatic ecosystem.
Metrics that scientists use to describe a habitat and examine macroinvertabrates include:
• richness measures
• composition measures
• stress tolerance or intolerance measures
• feeding measures
• habit measures
• life-cycle measures
The file below provides a key for identifying and aquatic macroinvertebrates. This key was developed with the assistance of John Flannagan. This key also helps classify the invertebrates into categories representing the kind of environments they live in. This, in turn, gives insights into the quality of the water.
To monitor Freshwater Macroinvertebrates, we want to estimate biodiversity, examine the ecology of the water body and explore relationships among water chemistry measurements and organisms. Most often it is impossible to count all individuals of every species present in a habitat, so we take samples of organisms from the habitat, and calculate the diversity found in these samples to estimate the biodiversity of the habitat. Biodiversity is the number of different kinds of organisms in an ecosystem and the population of that species. Biodiversity may be estimated from species data, or from broader categories like the number of different kinds of arthropods. Scientists often use metrics to learn about the ecology of the water body. Metrics are derived from counts of organisms in samples at a variety of sites. A simple metric is the number of organisms. Organisms can also be put into groups such as the percentages of organisms using specific feeding strategies (grazers, filter feeders, and predators), or percentages of long-lived and short-lived taxa.
Taking chemical measurements in a water body is like looking at a picture of what is going on in the water at that time. Taking biological measurements is like watching a movie of things that happened over time in the water in a single visit. Macroinvertebrates record the history of a water body because many are sessile (stay within a small area) and live one or more years while the water flows by. Changes in the habitats (including water chemistry) most likely will cause changes in the macroinvertebrate assemblage.
Using macroinvertebrates to indicate how stressed the water body is:
Scientists studying ecological systems are often interested in what happens to organisms exposed to stress. Stresses can be caused by natural events or human activities. An example of a natural stress in an aquatic system is a major storm that causes extensive flooding. Many macroinvertebrates may die or be washed away. The flooding may cause mud to be deposited in areas that were mainly gravel. This will cause a change in the types of macroinvertebrates that can live there. Macroinvertebrate metrics are often designed and used to examine the types of stresses affecting water bodies by the way macroinvertebrate communities respond to conditions affecting their habitats. By examining data on abundance of different taxa in respect to the macroinvertebrate characteristics such as ecological roles of these taxa in the ecosystem and their tolerance to stress, one can learn much about the aquatic ecosystem.
Metrics that scientists use to describe a habitat and examine macroinvertabrates include:
• richness measures
• composition measures
• stress tolerance or intolerance measures
• feeding measures
• habit measures
• life-cycle measures
The file below provides a key for identifying and aquatic macroinvertebrates. This key was developed with the assistance of John Flannagan. This key also helps classify the invertebrates into categories representing the kind of environments they live in. This, in turn, gives insights into the quality of the water.
aquatic_invert_08.pdf | |
File Size: | 889 kb |
File Type: |
The file below provides a spreadsheet that calculates water quality based on the counts and orders of the macroinvertebrates found in the water sample. Enter your counts in the appropriate categories and the spreadsheet calculates a water quality index. The spreadsheet is set up to accommodate entries from a number of sub samples taken by different groups of students.
total_invert_countwith_score.xls | |
File Size: | 25 kb |
File Type: | xls |
Freshwater benthic macroinvertebrates comprise only three of the many animal phyla – Arthopoda, Annelida, and Mollusca. Almost all of the freshwater benthic macroinvertebrates you will encounter fall within the taxnomic groups below.
Phylum
|
Arthropoda
(crustaceans, insects, spiders, and relatives)
|
Annelida(segmented worms)
Oligochaeta (aquatic earthworms) |
Mollusca(mollusks)
|
Class
|
Malacostraca
(crayfish, pill bugs, shrimp, and relatives) Insecta (see Orders below |
Hirudinea
(leeches) Oligochaeta (aquatic earthworms) |
Gastropoda
(gastropods, slugs, and freshwater snails) Bivalvia (bivalves, mussels and clams) |
Order
|
Ephemeroptera
(mayflies) Odonata (dragonflies and damselflies) Plecoptera (stoneflies) Hemiptera (true bugs) Trichoptera (caddisflies) Lepidoptera (butterflies and moths) Coleoptera (beetles) Megaloptera (alderflies, dobsonflies, fishflies) Neuroptera (spongillaflies) Diptera (two-winged or true flies) |
Basommatophora
(freshwater snails) Unionoida (freshwater mussels) Veneroida (asian clam) |
Procedures for collecting samples of aquatic macro-invertebrates
The gear used in collecting invertebrates:
This picture shows the equipment that is used in collecting, sorting, classifying and analyzing the sampled aquatic invertebrate. It includes:
- Schuber swift water sampler screen
- bucket for sample collection
- white tray for sample sorting and analysis
- small plastic cups for collecting sorted invertebrates
- loupe for examination and classification
- sucker-upper (large opening eye dropper)
- identification key
How to use a Schuber swift water sampler
The picture to the left shows the Schuber sampler worked into the stream bed, in this case rocks and gravel. Work and kick up sediments upsteam of the screen so that the current takes finer materials and macroinvertebrates into the screen. Clean pebbles and rocks that wash into the screen in the screen and remove the larger rocks. In quiet waters draw the sampler through bottom sediment. If the sediment is muddy, wash the screen multiple times to clear away most of the fine sediments, leaving the macroinvertebrates and other objects behind.
Sorting and counting the sampled macro-invertebrates
Place the screen into a bucked with some water in the bottom. Invert screen and wash the sample into the bucket. Pour the contents of the bucket into a number of shallow trays so that the macro-invertebrates are visible. The goal now is to sort and count the different types of invertebrates into small cups, each containing the same kinds of organisms. Invertebrates are sucked up in the larger droppers that do not damage them. The smaller cups so allow for closer examination, with additional sorting and counting.
Analysis of the sample
Once the identification and counting has been completed, enter the results into a column of the group spread sheet. If a number of trays have been examined by a class, you would expect a fairly high degree of similarity between the counts for each tray, given that they all originated from the same bucket. This is an opportunity for students to exchange their samples, re-sort and classify to see if the results remain the same. Once all the groups have entered their data, use the spreadsheet to calculate a water quality index score.
NOTE: It is important to understand that population counts are also indicators of water quality. Check over the interpretative scale on the chart to see how this works.
NOTE: It is important to understand that population counts are also indicators of water quality. Check over the interpretative scale on the chart to see how this works.