Macroinvertebrate Habitat Availability and Utilization on the Eno River

Abstract

Increasing competition between offstream and instream water uses emphasizes the need for accurate and equitable river management decisions. Minimum instream flow requirements necessary to sustain aquatic diversity can best be determined through habitat classification and modeling. Although previous studies focused on fish communities, the flow needs and responses of other organisms to inevitable flow disturbances vary greatly depending on the trophic level and mobility of the species considered. This research attempts to quantify and describe the available habitats and the suitability of those habitats for macroinvertebrates in the Eno River, as well as highlight management strategies consistent with invertebrate preferences. Through field sampling two sets of data were collected: macroinvertebrate counts and measurements of the physical habitat parameters of depth, velocity, and substrate. The habitat parameters were subset into utilization and availability data. Utilization data described parameters where macroinvertebrates were collected and availability data described all parameters whether macroinvertebrates were collected or not. Results showed that the habitat used by macroinvertebrates was the same as the available habitat meaning, in theory, that the macroinvertebrates can choose their habitat because it is the most suitable for them not because it is the only habitat available. Suitability indices for several macroinvertebrates revealed that low and mid depths and low and mid-high velocities were the most common optimal habitat types. Substrate suitabilities were greatly varied although many species favored aquatic vegetation, sand-gravel, and cobble-boulder combinations. The results of this study will be an important element in the formulation of instream flow management plans in the state of North Carolina. Additionally, the suitability curves could be used by professionals interested in stream restoration, water quality, and aquatic resource management to help them preserve macroinvertebrate diversity and in the process the health and functionality of aquatic ecosystems.