Nina Keul, University of Kiel, Kiel, GERMANY, Dieter Garbe-Schönberg, CAU Kiel, Institute of Geosciences, Kiel, Germany, Katja Peijnenburg, Naturalis Biodiversity Center, Leiden, Netherlands and Gerald Langer, Universitat Autònoma de Barcelona, Institute of Environmental Science and Technology (ICTA-UAB), Bellaterra, Spain