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Macroinvertebrate Studies (Bugs, bugs and more bugs!)

Macro -- (From Greek makro, form makros long, large)
Invertebrate -- (in ver te brit), biology -n. an animal without a backbone or vertebrae. Worms and insects are invertebrates, in contrast to such vertebrates as fishes, amphibians, and reptiles

The term macroinvertebrate refers to animals without a defined backbone, including crustaceans, mollusks, worms, gastropods and insects. Macroinvertebrates serve as important biological indicators, making them of interest to Las Vegas Wash biologists.

Due to their abundance and varied sensitivities to environmental changes, they are used to assess the health of a stream. As grade control structures are built to restore wetland ecosystems in the Wash, the effectiveness of efforts to re-create habitat need to be gauged. Studying macroinvertebrates in and along the stream as well as within revegetation areas is a great way to determine the health of the Wash.

Dragonfly

The Benthic Macroinvertebrate Study

Purpose

The purpose of the Benthic Macroinvertebrate Study is to determine how erosion control structures and associated wetlands impact the benthic macroinvertebrate fauna of the Las Vegas Wash. This will be achieved through the documentation of the macroinvertebrate population at selected locations in the Las Vegas Wash. The results will be helpful for the prediction and planning of habitat improvement measures that may be incorporated with future grade control structures.

Sampling Sites

Twenty-six sites (shown on the map below) have been selected for sampling. These include multiple locations along the Wash as well as three tributaries and reference locations upstream of the Clark County Water Reclamation discharge.

Macroinvertebrate Study Sample Sites

Field Protocol

Using a D-frame dip net biologists sample a variety of habitats that are present in the Wash such as boulders, cobble, woody snags, aquatic vegetation and sand. By "kicking" or disturbing the substrate and sediments within approximately 1 to 2 feet of the net, organisms are set loose and the current carries them into the net. Each sample is preserved in the field with a 70 percent alcohol solution. Macroinvertebrate samples are then brought back to the laboratory for identification and enumeration.

Results

The study is ongoing and is now conducted on a quarterly basis by U.S. Bureau of Reclamation biologists of Las Vegas Wash Coordination Committee. The continued collection and annual reports will allow us to determine how the macroinvertebrate population in the Wash is changing as a result of stabilization and enhancement activities. In addition, the data collected from the Wash's unique ecosystem, stabilization efforts and history can inform others working in these types of systems about what we have found through published research papers.

Terrestrial Macroinvertebrate Studies

In addition to the surveys conducted within the Wash itself, a wide variety of surveys are conducted to better understand the invertebrates found outside of the water as well. Collections and identifications are made year-round in all types of habitats; emergent vegetation, riparian areas, mesquite bosques and upland desert. The variety of habitats has led to a wide variety of species being found. So far, more than 375 invertebrate species have been identified along the Wash (this includes those collected in the Benthic Macroinvertebrate Study).

Specific studies have included comparing butterfly populations in areas that were mostly covered by non-native vegetation such as common reed and salt cedar to areas that had been revegetated with native species. The study showed that the native vegetation areas had higher abundance and diversity of insects than areas dominated by non-native species such as common reed and tamarisk.

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Las Vegas Wash Project Coordination Team • 100 City Parkway, Suite 700 • Las Vegas, NV 89106 • (702) 822-3300