1. Department of Environmental Sciences; University of Helsinki; P.O. Box 65 Helsinki 00014 Finland
2. Tvärminne Zoological Station; University of Helsinki; J. A. Palménin tie 260 Hanko 10900 Finland
3. Institute of Marine Sciences (ICM-CSIC); Passeig Marítim de la Barceloneta 37-49 Barcelona 08003 Spain
4. GRC Marine Geosciences; Department of Marine Stratigraphy, Paleontology and Geosciences; University of Barcelona; Carrer Martí i Franquès s/n Barcelona 08028 Spain