1. a Department of Biology, Section Protistology & Aquatic Ecology, University of Gent, K.L. Ledeganckstaat, 35, B-9000 Gent, Belgium
2. b Royal Botanic Garden, Edinburgh EH3 5LR, UK
3. c National Institute of Water & Atmospheric Research Ltd, Riccarton, Christchurch, PO Box 8602, New Zealand
4. d British Antarctic Survey, Cambridge CB3 0ET, UK