Benthic Macro Invertebrate As Biological Indicator
Benthic macro invertebrates live in a wide variety of habitats and can be found from the smallest headwater streams down to the largest rivers. 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.
Benthic macro invertebrates tend to remain in their original habitat; they are affected by local changes in water quality. Some are capable of tolerating higher loads of pollution than others. Although the abundance of certain species may increases, the diversity and species richness decrease. By assessing indicator species, and functional groups of the benthic macro invertebrate community, it is possible to test water quality. Macro invertebrates are sensitive to changes in pH, dissolved oxygen, temperature, salinity, turbidity and water chemistry.
Sources of food for benthic communities can derive from the water column in the form of aggregations of detritus, inorganic matter, and living organisms. These aggregations are important for the deposition of organic matter, and bacterial communities. This amount will vary on the depth of the benthos, and the degree of benthic-pelagic coupling. The benthos in a shallow region will have more available food than the benthos in the deep sea. Because of their reliance on it, microbes may become spatially dependent on detritus in the benthic zone. Benthic macro invertebrates have many important ecological functions, such as regulating the flow of materials and energy in river ecosystems through their food web linkages. Because of this correlation between flow of energy and nutrients, benthic macro invertebrates have the ability to influence food resources on fish and other organisms in aquatic ecosystems. For example, the addition of a moderate amount of nutrients to a river over the course of several years resulted in increase in invertebrate richness, abundance, and biomass.