Skip to main content

Aquatic Ecosystem Exploration

Unit Plan: Ecosystems in Action: Cycling of Matter & Energy, Natural History of the Hudson RiverTime: Two-four 45-minute lessons Setting: Aquatic ecosystem, classroom
6-8, 9-12Hudson River Ecology
icon quick tip

Use the filter to limit your results.


Students will know how an aquatic ecosystem works and be able to collect representative organisms, identify the organism and its trophic level, and create a food web of a local aquatic ecosystem.


    Students visit a local stream, pond, creek, or river and collect macroinvertebrates

    Students sort macroinvertebrates and identify each species using a dichotomous key

    Students decide on trophic levels and construct a possible food web for their ecosystem


    Day 1:

    • Nets
    • Waders
    • Collecting trays
    • Magnifying glasses
    • Collecting jars
    • Permanent markers
    • Tweezers
    • Strainers
    • Macroinvertebrate keys
    • Isopropyl alcohol (if you need to preserve the animals for the next class period)


    Day 2:

    • Dissecting microscopes
    • Lights
    • Petri dishes
    • Magnifying glasses
    • Reference keys
    • Tweezers
    • Pipette

    Engagement: Students should already be excited and interested in the field trip. You can use a pond, stream, river, or creek. Remind students of appropriate safety precautions. Look for a pond that has emergent vegetation along most of its shoreline, floating plants, dragonflies, frogs and a minimum of invasive exotic species such as common reed (Phragmites australis) and purple loosestrife (Lythrum salicaria). Most streams and creeks will have a good representation of macroinvertebrates. Unless you or your institution owns the habitat, be sure to obtain permission of the landowner to access the property and collect organisms.


    Day 1: Divide the class into groups of three or four students and provide each group with a data sheet, a macroinvertebrate key, and some supplies. At least one student in each group will need to wade in the water in order to sample its biodiversity. It is best to obtain one pair of waders per group. If waders are not available, the students should be told to wear shorts and bring a hand towel and an old pair of sneakers to class.
    After the introduction give the students time to observe the ecosystem and record their group’s observations on the data sheet. This information will be needed later to develop the aquatic food web.
    Tell the students that one of the goals of this lab is to sample the biodiversity of the pond and to make a comprehensive list of all the organisms in the aquatic ecosystem. Ask them how they would do this for fish and emergent plants. Tell the students that in the time allotted it is not possible to systematically sample all the organisms, so today’s lab will focus on macroinvertebrates, which are often important indicators of water quality.
    Following the instructions in the lab handout, demonstrate how to use the aquatic net, emphasizing the need to keep the flat edge of the frame near the bottom. Dump the catch in a tray and show the students how to find and collect the animals. There is a tendency to overlook small things. Be sure that they understand that they need to put each different kind of invertebrate in a different container. Give the students as much time as possible to do their share of the sampling for aquatic organisms.
    The lab handout instructs that students to count and record the number of organisms of each type and to save two or three of each in a small amount of water. Encourage them to count carefully. The numbers are important for the next lab.
    If possible, keep the animals alive for the beginning of the identification part. This helps because the students can see how they behave normally. Then, the water can be removed from the jars and replaced with 70% ethanol or isopropyl alcohol to preserve the specimens. Pouring the collection through a small dip net or cheesecloth prevents the loss of small organisms.
    Day 2: After students have returned to the lab and can sort their organisms, introduce the use of a dichotomous key by using one of the larger specimens. Some couplets in the key may need explanation. The students do not generally seem to realize that the hard outer coatings of beetles are actually “wings,” and they tend not to recognize “wings hard and shell-like.” Similarly, beak-like mouthparts are hard to see and wing pads and developing wings are difficult to recognize. Pointing out these features and/or providing pictures reduces errors in using the key.
    Students will probably not be able to identify everything they collected. A few unidentified few specimens should be expected and it will not make a difference in the results when the class data are pooled for analysis.

    Explanation: Students should be reminded of trophic levels and the relationship between organisms in a food web. If necessary, review these concepts as a class. Once students have completed their survey of the organisms, they should report their results on the board. All students are responsible for the class data, from which they can calculate relative abundance. Do one together as an example. Discuss the concepts of abundance/numbers, diversity, richness and dominance. Despite efforts to get a representative sample of macroinvertebrates, the collection may contain too many predators, especially dragonfly and damselfly nymphs and water boatmen. These organisms may be overrepresented because they are big and easy to collect. Ask the students to think about the class data and the relative abundance of the different trophic levels. Primary consumers (herbivores) are usually more abundant that secondary consumers (predators).

    Extension: Students can use a compound microscope to look at a drop of water under magnification and attempt to extrapolate the number of organisms in the entire sample based on what they see.

    Evaluation: Students should be able to construct a local food web and discuss the connections between biotic and abiotic components of the ecosystem.  


    Lesson Files

    Lab Worksheet
    Field Handout
    Macroinvertebrate Collection Sheet
    Dichotomous Key with Pictures
    Dichotomous Key without Pictures
    Pond Data Sheet
    Pond Lab Handout
    Pond Invertebrate Biology Briefs
    Stream Invertebrate Biology Briefs
    Common Invertebrates of the Hudson Valley

    Benchmarks for Science Literacy

    5A Diversity of Life, 5D Interdependence of Life, 5E Flow of Matter and Energy, 9B Symbolic Representation, 9D Uncertainty

    NYS Standards

    MST 1 - Mathematical analysis, scientific inquiry, and engineering design, MST 2- Informational Systems/ Information Technology, MST 4- Physical setting, living environment and nature of science, MST 5- Engineering and computer technology to satisfy societal needs, MST 6- Interconnectedness of mathematics, science, and technology (modeling, systems, scale, change, equilibrium, optimization), MST 7- Problem solving using mathematics, science, and technology (working effectively, process and analyze information, presenting results)
    Next Generation Science Standards

    Science and Engineering Practices

    Planning and carrying out investigations, Engaging in argument from evidence

    Cross Cutting Concepts

    Cause and effect

    Disciplinary Core Ideas

    PS3A: Definitions of Energy
    New York State Science Learning Standards

    Performance Expectations

    MS-LS1-4. Use argument based on empirical evidence and scientific reasoning to support an explanation for how characteristic animal behaviors and specialized plant structures affect the probability of successful reproduction of animals and plants, respectively.