Measuring the intensity of disturbancein zooplankton communities of Mediterranean salt marshes using multivariate analysis

Abstract

The possibility of using multivariate analysis for measuring disturbance intensity in fluctuating ecosystems is discussed. As an example, two variables derived from the results of correspondence analysis of aquatic invertebrate samples from the Aiguamolls de l’Emporda (NE Spain), Mediterranean salt marshes, are proposed as measures of the severity and intensity of disturbance. The behaviour of these variables allows us to discuss several topics of disturbance theory, such as the relationship between disturbance intensity and the distribution of planktonic biomass by size, stability and diversity. A better adjustment to a curve (r 2 = 0.743) is obtained when testing Connell’s intermediate disturbance hypothesis when evenness and severity are used to measure diversity and disturbance, respectively. This hypothesis may be expressed as follows: at intermediate severity, the maximum links between present species are found. These measurements are simple to obtain and may be useful tools for the management of Mediterranean ecosystems. Although they cannot be directly applied to other ecosystems, a relationship between multivariate results and measurements of disturbance might be observed in similar ecosystems if analogies between some multivariate results and the flux of external energy are investigated.