Index of Biological Integrity(IBI)

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Index of Biological Integrity(IBI)-The following is from a paper by Dr. Steve Gordon of the Ohio State University. For the entire paper please click here.

The IBI index was first developed by Karr in 1981 and was later modified by the Ohio EPA in 1987 for specific use in Ohio . There are 12 individual community metrics incorporated into the summary IBI score, which when aggregated, provide a consistent and sensitive measure of biotic integrity (Ohio EPA 1988). The metrics can be grouped into three main categories: species richness and composition fish abundance and condition and trophic composition (Karr 1981).  At a given sample site in a stream, a score is given to each metric in relation to whether it closely (5), somewhat (3) or fails to (1) approximate the reference site. Each metric assesses fish community attributes that are inferred to be either positively or negatively correlated with stream biotic integrity (Ohio EPA 1988). With 12 metric scores, the maximum IBI value obtainable at a given site would be 60 (12x5) and a minimum would be 12 (12x1). The following is a brief description of the metrics comprising Ohio EPA’s IBI detailed by Ohio EPA (1987).

• Total Number Species - direct community diversity measure and general indicator of environmental quality

• Number of Darter Species/ Percent Round-Bodied Suckers - site specific species requiring clean water. Darters are found in headwater or wading stream and represented by round-bodied suckers in boating sites

• Number of Sunfish Species/ Number of Headwater Species - favor quiet pools and in-stream cover; indicate degree of preservation of original pools and riffles and channel components of the stream reach

• Number of Sucker Species/ Number of Minnow Species - relatively long- lived and favor high environmental quality; serve as long-term indicators of surrounding conditions

• Number of Intolerant Species/ Number of Sensitive Species - serve as indicators of degradation; greater proportion of intolerant species indicates less degradation

• Percent Tolerant Species - serves as indicator of degradation; greater proportion of tolerant species signifies a greater degree of degradation

• Percent Omnivores - represents degree of disruption to the food base; greater proportion of omnivores indicates greater environmental degradation

• Percent Insectivores - measures community integrity in the middle of the food chain; fewer insectivores suggest depletion of insect food base and therefore a greater degree of environmental degradation

• Percent Top Carnivores/ Percent Pioneering Species - measures fish species at the top of the food chain; more carnivores suggest a greater food base and therefore a relatively good community structure

• Number of Individuals - excluding tolerant species, serves as a measure of toxic sensitivity and total degradation

• Percent Hybrids/ Number of Simple Lithophilic Species - indicate levels of stress and disturbance in stream reach; lithophilic spawners require clean gravel or cobble and are a good indicator in non-headwater streams

• Percent DELT Abnormalities - measures Deformities, Eroded fins, Lesions or Tumors and usually indicate overcrowding, disease or high levels of toxicity

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Last updated: April 7, 2009.