BMI Collection

BMIs are animals without a backbone that can be seen with the naked eye, and have to the ability to cling to bottom surfaces such as rocks, leaves or roots. They include crustaceans, mollusks and annelids but in many aquatic environments most of the macroinvertebrate community are the larvae of aquatic insects. These communities are important links in the food web between producers (leaves, algae) and higher consumers such as fish, and are key indicators of biological integrity in streams, rivers and wetlands.

Depending upon the stream environment a variety of methods and equipment are used to collect benthic macroinvertebrates from wadeable streams. In rocky-bottom streams, WV Save Our Streams recommends using a two-pole screen-barrier net (commonly known as a two-pole kick-net) or a single pole rectangular style kick-net (sometimes called surber on a stick). Both types should be equipped with 500-micron mesh netting. Two-pole kick-nets require at least two people working together to collect the sample. Groups may purchase other nets as needed but only the two-types discussed here are recommended for rocky-bottom collections. D-nets are used for macroinvertebrate collections from low gradient and wetland habitats. Low-gradient streams and wetlands require a much more intensive collection procedure. Ultimately, the types of nets used depend upon the goals and objectives of the volunteer monitoring program and the kinds of streams they plan to monitor.

The second person approaches the sample area from upstream and determines the approximate sample-size. Once the area is delineated, the sampler begins disturbing the streambed directly in front of the net. The process starts with rock rubbing. First, pick-up all large rocks (cobble size and larger) and inspects them. You are looking for snails, clams and caddisfly cases. These animals often cling very tightly to the rocks and are not removed by just a simple rub with the hands or a small brush. If the rocks have any of these animals, remove them from the rocks and place them inside the bucket. Move the rocks you picked-up towards front and slightly into the net; brush all sides of the rocks with your hands or a small vegetable-brush to dislodge other clinging macroinvertebrates. Continue the rock rubbing process until the larger sized stones have been thoroughly cleaned. If the rocks cannot be lifted from the streambed, simply rub them where they lay. As much as possible the rock rubbing should proceed from the upstream portion of the sample area towards the front of the net. After the rocks are rubbed they should be placed aside (outside of the sample area) so they are not rubbed a second time.

Some volunteer programs choose a timed approach to rock rubbing since this is a rather intensive and somewhat time consuming step. The recommended time frame for adequate rock rubbing is four - six minutes (or less) depending upon the abundance of cobbles and boulders within your sample area. If you choose a timed approach you should make a note on the survey data sheet and record the time frame you use. The recommended kick-time is two minutes, so your entire sample should take about six - eight minutes to collect.

This is a very important step; since the sample collection is laborious you do not want to lose any of the macroinvertebrates collected by sloppy procedures here. Very slowly remove the rocks that have acted as anchors to hold the kick-net in place, rub them off while you remove the rocks, or you may choose to rub them before using them to anchor the kick-net in place. While the net-holder grabs and holds the top of the net in-place the kicker grabs the bottom edge of the net near the handles. The net is removed with a scooping motion, the kicker moved slightly forward and upward while the holder keeps the net steady so that no macroinvertebrates are lost from washing over the top of the kick-net. Both persons then pick-up the net and roll it into a loose cylinder, securing the ends and taking it to the shoreline. The collection bucket should be at the ready to accept the contents of the kick-net.

The goal of this step is to remove all captured macroinvertebrates so that they can be observed, identified and counted. WV Save Our Streams recommends that you use several shallow white trays. The best way to start is by trapping the macroinvertebrates as they are poured from the bucket. Before starting the steps below, remove all larger materials that may have been collected with your sample from the bucket. Make sure to check these for macroinvertebrates before they are discarded. At certain times of the year leaves and other debris are very plentiful in the stream and this material must be sorted. (It is common to find many kinds of macroinvertebrates in leaf-packs; this material is one of their favorite places to live.) The best way to deal with the leaves is to remove as many as possible, place them in smaller bucket or container and wash them to remove the macroinvertebrates. Pay close attention to the leaves that appear chewed and have begun to decay. Newly fallen leaves are less likely to have many macroinvertebrates. You can use a second bucket with your kick-net on top, and then pour the captured organisms over the net so that they are trapped against the net. The pouring is stopped periodically so that the macroinvertebrates can be removed from the net and placed into the collection trays. Small forceps are the best tool for this job; however the macroinvertebrates can also be removed by hand. The easiest method is to use a wash bucket or EZ-strainer. The EZ-strainer is available in a variety of mesh sizes and fits nicely inside a 3 ½ or 5-gallon bucket. Your collections are poured directly into the EZ-strainer, or into a second bucket and then into the strainer if additional washing is necessary. See additional information for some homemade equipment ideas.

If your organization decides to complete independent surveys that include aquatic collections, you must apply for and receive a Scientific Collection Permit from the WVDNR. See additional information to view the SOS Program's permit.