Assessing the state of an ecosystem solely on the basis of short-term changes in the number of different species it contains can lead to false conclusions. This is the conclusion reached by an international team including researchers of the Helmholtz Institute for Functional Marine Biodiversity (HIFMB) at the University of Oldenburg and the German Centre for Integrative Biodiversity Research (iDiv). In order to assess ecosystems in a way that is meaningful for nature conservation, experts should instead focus on analysing the turnover of species within a system. The researchers reached this conclusion using a mathematical model and environmental data analysis. The new method can be applied effectively using data already available from environmental monitoring programmes. The study is published online in the Journal of Applied Ecology.