MCI stands for Macroinvertebrate Community Index which is an index where macroinvertebrates are used for monitoring and reporting on stream health in New Zealand. The MCI assigns a score to each species or taxon (from 1 to 10), based on its tolerance or sensitivity to organic pollution, then calculates the average score of all taxa present at a site. It is a qualitative sampling method, which means it will tell you which species are present or absent in your sample. If you want to know the abundance (i.e., how many) of a certain species are in your sample, you will need to use the Quantitative MCI (QMCI) sampling methodology.
View a factsheet on Benthic macroinvertebrates