Benthic macroinvertebrates research | Cloudbridge Nature Reserve in Costa Rica

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Benthic Macroinvertebrate Monitoring

A research project at Cloubridge Nature Reserve in Costa Rica
"In the end, we will conserve only what we love, we will love only what we understand, we will understand only what we are taught."
Bada Dioum, Senegalese conservationist

Cloudbridge is seeking an enterprising research volunteer to conduct this study.

Benthic macroinvertebrates
Benthic Monitoring is the collection of critters (insects and other invertebrates) from the bottom of a river or stream. Benthic means bottom dwelling and refers to the organisms that live in, crawl upon, or attach themselves to the bottom (or substrate) of the river. Macro means large (in this case, visible to the human eye) and invertebrate refers to animals without backbones. Most benthic macroinvertebrates are aquatic insects or the aquatic stages of insects. They also include such things as clams and worms.

Why study macroinvertebrates?
Benthic macroinvertebrates are an important part of river ecosystems. Stream dwelling invertebrates respond to changes in the physical and chemical environment. Benthic macroinvertebrates generally inhabit a localized area of a stream throughout their life cycle. Therefore, the individual organisms are continually exposed to any changes that occur in the chemical and physical environment. Collecting macroinvertebrates can provide an understanding of a river's condition. Because many macroinvertebrates live in the stream year-round and sometimes over multiple years, their presence or absence provides valuable information about a river's health over time.

Methodology and equipment
(Adapted from green.org)
The method described here generally follows a qualitative or semi-quantitative approach. It has been used successfully by non-biologists to monitor water quality and identify trouble spots.

Choose a 3-foot by 3-foot area in a riffle typical of the stream. A riffle good for sampling will have cobble-sized rocks, fast moving water, and a depth of 3 to 12 inches.
Use the kick seine method to collect the sample. Enter the water downstream of your sampling location. Have one person hold the poles on the net upright in the sampling area and push the poles firmly into the substrate. No water should wash under or over the net. Place small rocks on the bottom edge, if needed, to hold it down.
As the net is held, a second person brushes all organisms off the cobbles and rocks. Completely brush rocks and set them outside the sampling area. Next, stir the substrate to a depth of several inches to dislodge any burrowing macroinvertebrates. You can use a metal tool, such as a long screw driver, or use your feet in a shuffling motion to kick the substrate toward the net. Stir for at least one minute.
Lift the kick seine out of the water with a forward scooping action to avoid losing macroinvertebrates off the end of the screen.
After carrying the seine to the stream bank, wash the contents into a large bucket filled with stream water. Washing from behind the screen helps to dislodge the animals. Use only stream water for rinsing organisms off the net into the bucket. If you plan to sort back at your lab or school, you can transport the sample in the large bucket, preferable with a lid, with plenty of stream water.
You can begin sorting directly from the bucket into ice cube trays or other sorting containers filled with stream water. However, it is often easier to scoop parts of the sample into shallow pans from which to sort. Keep scooping and sorting until you've identified the entire sample (or reached whatever maximum number of organisms your program prescribes). Sort the different taxa (types of specimens) into separate containers or sections of the ice trays.
Once you have sorted the organisms, they can be identified in the field or lab using identification keys and guides.
Record the results of your assessment using the Benthic Field Data Sheet.

Additional information useful for stream site characterizations include: canopy cover, stream bed substrate, flow, turbidity, water temperature, acidity (pH), and dissolved oxygen. Detecting degradation through evaluation of invertebrate communities requires establishment of a description for reference condition. This is the focal point for developing analytical tools commonly used to evaluate stream condition and "biological integrity".

The following equipment is recommended by green.org for collecting benthic macroinvertebrates:

Kick seine or kick net (or other sampler) - for collecting sample.
Metal screw driver (or similar device) - for stirring the sample substrate.
Large white sheet or plastic - to lay out all equipment, keeping it clean and in one place.
Large buckets - for washing sample out of net and/or for transporting for later identification.
Plastic scooping devices (large measuring cups or modified plastic milk jugs) - to rinse insects off net (using river water) into collecting bucket or pans.
White enamel or shallow plastic pans - for dividing the sample for multiple groups; for picking and sorting from.
Ice cube trays, white preferable - for sorting the organisms by major group.
Small jars or vials - can be used for sorting and are especially helpful if you want plan to save and transport your sorted sample.
Seventy-percent alcohol solution - if you plan to save your sample.
Forceps/tweezers, spoons, small paint brushes - for picking organisms and sorting organisms into major groups.
Hand-held magnifiers - to aid in identification.
Vegetable brushes - to gently remove attached organisms from rocks.
Rubber boots or hip waders and rubber gloves - to keep you dry and warm during collection.
Meter stick - for making depth measurements.
Thermometer - for recording water and air temperatures at time of collection.

Identification and interpretation
Back in the house, you'll need data sheets, pencils, and clipboard - for recording sampling results. Also a field guide - to aid in identification of organisms (can be plastic coated for wet weather). Example: NY State Identification Guide or Save Our Streams Macroinvertebrate Identification Key. You'll then write a report that can be published and compared to future studies.

Interested in doing research at Cloudbridge?
Reseachers must bring independent funding for their projects, including travel and living expenses. There is also a US$100 fee (half goes to reforestation, and the other $50 is returned to you at the end of your stay). The cost of living in San Gerardo is low. Send us some information about your research qualifications, what you wish to study, and when you can come. If your project is accepted, we'll assist in finding accommodation and provide access to the reserve. We'll also publish the results of the research on the Cloudbridge website. To discuss your ideas, contact to Ian & Genevieve Giddy (see the contact page).