Macroinvertebrate distribution in streams: a comparison of CA ordination with biotic indices

Macroinvertebrates were collected in running waters in Italy, analyzed with correspondence analysis (CA) and with the calculation of 8 biotic indices. Then the CA ordination axes were correlated with 19 environmental variables and with biotic indices. The first CA axis is easily interpreted as an upstream-downstream gradient and is correlated with physical factors (particle size, slope etc.), whereas the second axis separated permanent waters from temporary ones. The first CA axis is correlated with many biotic indices suggesting that biotic indices are also strongly influenced by physical factors. Multiple regressions with 2 biotic indices as criterion and the 19 environmental factors as predictor variables confirm the importance of physical factors in determining the values of the biotic indices. The advantages and drawbacks of the use of CA instead of biotic indices is discussed.