Quantifying disturbances in benthic communities—comparison of the community disturbance index (CDI) to other multivariate methods

A multivariate index assessing community stress in marine benthic count data is compared to other multivariate methods. Both ordinations and clustering methods are included in the comparison and so is AMBI (AZTI marine biotic index). The community disturbance index (CDI) requires the data to contain undisturbed reference samples. If this requirement is met, the calculations are carried out in two steps. Firstly, the reference samples are separated and used to build a model representing the natural variation. Subsequently, the remaining samples are compared to the model and the respective disturbance indices are calculated. The CDI has the same sensitivity as the traditional multivariate methods. Additionally, one obtains a quantification of the relative level of disturbance. The comparison is performed using data from monitoring surveys at three different oilfields in the North Sea: Troll, Ekofisk and Oseberg-Brage. The samples are collected in 1996, 1990 and 1996, respectively.