Biological Monitoring

Habitats

Benthic macroinvertebrates live in a wide variety of habitats and can be found from the smallest headwater streams down to the largest rivers. In West Virginia, benthic macroinvertebrates are especially diverse, having adapted to the complex array of streams that dissect the mountains and tumble through the narrow valleys. In general, benthic organisms are most diverse in the fast flowing riffle and run areas of streams. Compared to pools and glides, riffles and runs are shallower and have higher stream gradients and faster water velocities. They are composed of rough materials, such as large gravel, cobbles and small boulders that create turbulence and oxygenate the water, while providing a stable habitat for benthos to live. Many insect benthos spend the majority of their lives (anywhere from 1 month to 4 years, depending on the species) in the water and only emerge as adults for a few hours (or up to several days) to reproduce and complete their life cycle. Movement of benthos larvae includes swimming, crawling around on the stream bottom and drifting with stream currents. After emerging, adult aquatic insects can fly to new stream locations during their winged terrestrial stage.

Adaptations

Benthic macroinvertebrates have special adaptations that allow them to live in the stream environment. These adaptations may be unique physical features or even specialized behaviors. For example, many species have flattened bodies that allow them to hide between boulders and cobbles, thus limiting the stress of fast-moving water and allowing them to avoid some predators. Others have sharp claws, suction cups, or other grasping mechanisms on their bodies to prevent them from being swept away in the swift-flowing current. Black fly larvae (Family Simuliidae) have a silk gland and posterior hooks that are used to anchor them in place while they face upstream actively capturing food with their fan-like mouth parts. Net-building caddisfly larvae (Family Hydropsychidae) construct funnel-shaped nets, attach them to stable substrate materials, and then periodically harvest the food caught in the mesh. Some stonefly species will avoid high water temperatures by burrowing deep into the stream bottom substrate where they will diapause near the water table. One of the most important adaptations for benthos is the ability to extract oxygen from the water in which they live. Many aquatic insects accomplish this with external gills that remove oxygen from the surrounding water, while others rely upon cutaneous respiration to obtain oxygen.

Feeding

Benthos are often classified based on their feeding strategy. The stonefly Pteronarcys (Family Pteronarcyidae) is in the shredder functional feeding group. These large stoneflies primarily consume decaying leaves that have fallen into the stream from trees along the forested riparian corridor. The water penny beetle (Family Psephenidae) is a scraper and can be observed grazing on algae that covers rocks and logs. The mayfly Family Baetidae is classified as a collector-gatherer, primarily feeding on fine pieces of organic material on the stream bottom. The most recognized predator in the aquatic insect world is the larval form of the dobsonfly, more commonly known as the hellgrammite (Family Corydalidae). Hellgrammites are active predators, crawling around on the large cobble and boulders in the swifter habitats of streams where they search for other benthic macroinvertebrates to eat.

Importance in Food Webs

Benthic macroinvertebrates are extremely important in aquatic food webs. In most streams, the energy stored by plants is available for consumption by benthos either in the form of leaves that fall into the water or in the form of algae that grows on the stream bottom. The energy derived by eating leaves and algae is then transferred from benthos to other life forms in and around the stream such as fish, frogs, salamanders, snakes, birds, and even fishermen. In another sense, benthos are important for recreational purposes, as thousands of trout anglers strive to "match the hatch" of many species, particularly those of mayflies.

Biological Indicators

Benthic macroinvertebrates provide reliable and comprehensive information on water and habitat quality and have been used as biological indicators in many parts of the world for nearly 100 years. In some cases, it may be difficult to identify pollutants and stressors in streams with chemistry data alone, which only provides information pertinent to the precise time of sampling. Even the presence of fish may not be indicative of the status of a stream because fish can swim away to avoid polluted water or unfavorable habitat conditions and then return when conditions improve. Many benthic macroinvertebrates are not as mobile as fish and cannot move to avoid pollution. Therefore, the community of benthos living in a stream may indicate the water quality conditions of the past. Additionally, benthos are excellent tools for assessing water quality because they are extremely diverse, allowing for a wide range of sensitivity and responses to stressors such as metals, nutrients and sediments. Finally, they are ubiquitous and relatively easy to collect and identify which makes them attractive to agencies and organizations searching for a practical means of assessing water quality in streams.

In order to extract and understand the information presented by a benthic macroinvertebrate sample, the WAB uses a tool commonly called an Index of Biotic Integrity (IBI). An IBI is a summary score that is comprised of several biological indicators called metrics. A metric is a characteristic of the biological community that changes in some predictable way with increases in human disturbance. For example, species richness (sometimes called diversity) generally exhibits a marked decrease as human disturbance increases. Therefore, it is one of the most commonly utilized component metrics of IBI's.

Family Level Benthic IBI

In 2000, the WAB collaborated with the United States Environmental Protection Agency (EPA) Region III to develop its own IBI, a multi-metric index for biological assessments called the West Virginia Stream Condition Index (WVSCI). The WVSCI summarizes family level identifications of benthic macroinvertebrate assemblages to assess the biological condition of wadeable streams with riffle/run habitats. This index includes six biological metrics that represent elements of the structure and composition of benthic macroinvertebrate communities. The WVSCI metrics were selected to maximize discrimination between streams with known stressors and reference streams. Reference streams have little or no human disturbances, and therefore exhibit good water quality and habitat conditions. Many of the streams that the WAB recognizes as reference sites are located on public lands, such as Monongahela National Forest and the West Virginia State Park system. The WAB used the WVSCI from 2002 to 2014 to assess the biological condition of wadeable streams in the state.

• WVSCI Document
• WVSCI Addendum
• Reference Document

Genus Level Benthic IBI

Although the family-level WVSCI was designed using sound ecological and statistical principles and has typically met the needs of the WAB, the availability of genus-level benthic macroinvertebrate data led to the development of an updated IBI in 2011. This IBI, referred to as GLIMPSS, was developed with geographical and seasonal partitioning that resulted in separate IBI’s for the plateau and mountain regions in WV as well as spring, summer, and winter seasons. Genus-level taxonomy allowed for the selection of several additional indicator metrics with larger response ranges that could better track stressors in different seasons and within specific geographic regions.

• GLIMPSS Development Report