An Introduction to Stream Ecology

Background for Teachers

This is a very brief introductory video on stream ecology by Dr. Stephen Coghlan, University of Maine, Orono. After watching the video students should draw and explain their interpretation of how a stream works (as presented in the video).  Steve’s approach is to follow matter and energy through the system. As our focus is on the macroinvertebrates that live in the system here is an overview:


Macroinvertebrates are animals that are visible to the naked eye and have no backbone. Most stream invertebrates are insects (either larval forms or adults) but, there are some that are not- worms, snails, mussels, crayfish and leeches to name a few.  This field chart can give you an idea of the diversity of macroinvertebrates:

Stream Foodwebs

Chances are very good that you have seen a food web before. For terrestrial (on land, often forest) food webs you might see something that looks like this:

Figure 1- source:

In this food web there are herbivores, carnivores and omnivores. There are also detritivores and decomposers. And most students can tell where they get their energy and materials for living:


Trophic level

Energy and materials for living from:






A little bit of everything


Intact dead things


Intact or already broken down dead things

While most food for terrestrial foodwebs comes from plants that are eaten right where they grow this is not the case for streams, especially small streams. Much of the plant material at the bottom of the stream food web comes from plant material that falls into the stream. The plant material may be consumed far from where it grew.

Most stream macroinvertebrates are omnivores—eating the plant material and the microbial organisms that have colonized the plant material.

Figure from-

This makes stream food webs a bit different than terrestrial foodwebs. The stream food web still traces how energy and materials for living move from organism to organism, but how animals eat becomes just as important as what animals eat.  Macroinvertebrates are classified by their functional feeding group- their feeding mechanisms--

Functional Feeding Group

Energy and materials for living from…

How they get their food…

Trophic level


Large pieces of leaves and tree pieces, and the bacteria and fungi that have already started to break down the plant material

Have strong, sharp mouthparts that allow them to shred and chew


Collectors (also called gatherers and filterers)

Smaller pieces of shredded plant material,and the bacteria and fungi living on the shredded plant material

Sieve the water through rows of tiny hairs or nets that they have spun. They may also have mouth parts that create a vacuum to suck things up


Scrapers (also called grazers)

Algae, fungi, bacteria, diatoms, tiny pieces of shredded plant material found on the surfaces of rocks and debris

Have scraping mouthparts

Herbivores (mostly)


Other living animals

Some engulf their prey—eating it whole or in parts. Others pierce their prey—eating live animal tissues



Why is this important? Because streams are such a patchy environment that the relative abundance of the different functional feeding groups can tell us a lot about stream conditions—much more so than classifying organisms into herbivore, carnivore and predator.

The stream food web is summarized (a larger version can be downloaded):


Students understand:

  • How the energy necessary for life moves through a stream system
  • That different stream organisms have different strategies and adaptations for eating


Students produce a diagram of a stream and explain, in their own words, how stream organisms get their food

Where does this lesson happen in the Project?

This lesson is in Unit 1: Building Background Understanding. It introduces the basics of stream ecology and should be used with the Habitat Connectivity lesson to begin the project.

Getting Ready

Ask your students to tell you anything they can about streams and what lives in streams- how many fish, what different types, what do they eat (ask the same questions if the students start with frogs or salamanders, as we are betting they will not start with macroinvertebrates)? Where do all animals ultimately get their food (plants)? Where are the plants in streams?  How do those non-fish organisms get their food? List all student information on a board.

Explain that, for this project, the students will need to understand how streams work as habitat for organisms and that they will be diagramming the stream system for themselves and then creating a reference diagram for the class to use while they are working on this project.



  • Video Question Sheet
  • Question Worksheet

Student Prerequisites

  • Students need to have a basic understanding of what a habitat is and that all organisms need energy to live
  • Our energy for living comes from the sun, through plants to other organisms and to us

Time Needed

One class period (or less), can be combined with the second activity in this Unit: Habitat Connectivity.

Doing the Activity

Ask students to share what they know about streams, or ask them to describe a stream that they are familiar with or have seen.

Watch the video. It is very short; you may want to watch it more than once.

After watching the video students should create their own diagram of the stream system and answer questions about the video. If possible, ask the students to create the diagram in the context of the stream that they are familiar with.

Students should share diagrams with each other and then make a general classroom stream system diagram- to be used as a reference as this project moves forward.



Have your students explain their stream system diagrams to each other, have students write down the questions that they have about the stream system and their diagrams.

Having watched Dr. Steve Coghlan’s video it may be possible for students to think about the how a stream changes from beginning to end. Have students draw an entire stream- is it exactly the same from start to end? Would the same creatures live in all parts of it? What might some differences be?

Ask a question; design a way to answer the question.

Using the Question Worksheet, ask students, individually, or in groups, to write down as many questions as they have about macroinvertebrates (individual species, interactions, competition, food preferences, habitat preference, etc.). From the list of questions have the students choose one or two. Ask the students to design a method to answer the question.  If there is time- present some of the questions and designs and discuss the merit of the research design.


Have students explain the stream system to their parents, siblings or another class.

Lesson Extensions and Supplements

Ask students to bring in a picture of a stream (or using classroom resources they can find a picture of a stream). Share those pictures, look for and discuss similarities and differences in the pictures.

Ask about things you cannot see:

  • What do you think the bottom is like?
  • Do you think the water is warm or cold?
  • How deep do you think this stream is?