1. Higher Council of Scientific Research-Institute of Natural Resources, Serrano 115 dpdo., E-28006 Madrid, Spain
2. Swedish University of Agricultural Sciences, Department of Aquatic Sciences and Assessment, P.O. Box 7050, SE-750 07 Uppsala, Sweden, and Institute of Environmental Sciences, University of Castilla-La Mancha, Av. Carlos III s/n., E-45071 Toledo, Spain
3. Higher Council of Scientific Research-Royal Botanical Garden, Pza. Murillo 2, E-28014 Madrid, Spain