Arnold H. Pieterse,^* Marianne Kettunen,^** Sara Diouf,^*** Ismael Ndao,^**** Khady Sarr,^**** Anne Tarvainen,^***** Sandra Kloff,^****** Seppo Hellsten<sup>*******


*</sup>Arnold H. Pieterse is a senior ecologist and staff member of the Royal Tropical Institute, Amsterdam, The Netherlands. His research involves weed research in the tropics, water purification and environmental management. He has coordinated various research projects in developing countries and Eastern Europe. His address: Royal Tropical Institute, Department of Rural Change, P.O. Box 95001, 1090 HA Amsterdam, The Netherlands. arnoldhp@planet.nl
^**Marianne Kettunen is an ecologist recently graduated from the Department of Biology, University of Turku, Finland. She is specialized in environmental conservation and management in tropical countries and wrote her Master’s thesis about the ecological and socioeconomic impacts of the invasion of Salvinia molesta in Senegal. Her address: Centre for Biodiversity, University of Turku, FIN-20014 Turku, Finland. marianne.kettunen@mantsy.fi.
^***Sara Diouf is deputy director of the National Parcs in Senegal. His address: Ministère de l’Environnement, Direction des Parcs Nationaux, Dakar-Fann, Senegal. dpnsbpnd@telecomplus.sn
^****Ismael Ndao and Khady Sarr are geographers working for the National Parks in Senegal. Their address: Ministère de l’Environnement, Direction des Parcs Nationaux, Dakar-Fann, Senegal. dpnsbpnd@telecomplus.sn
^*****Anne Tarvainen is a research scientist at the Finnish Environment Institute, Helsinki, Finland. She is specialized in tropical aquatic ecology and ecological changes caused by water-level regulation. Her address: Finnish Environment Institute, P.O. Box 140 FIN-00251 Helsinki, Finland. anne.tarvainen@environment.fi
^******Sandra Kloff is an independent consultant on aquatic ecology. She worked 2 years with the IUCN in Mauritania and is currently working in the south of Spain on integrated coastal zone management. Her address: Avenida Principe de Asturias, 40-7A, 11300 La Linea de la Concepcion, Spain. srkloff@hotmail.com
^*******Seppo Hellsten is a senior research scientist and staff member of the Finnish Environment Institute, Oulu, Finland. His research is focused on aquatic ecology of regulated and modified water courses with a special topic of aquatic macrophytes. His address: Finnish Environment Institute, P.O. Box 413, FIN-90101 Oulu, Finland. seppo.hellsten@ymparisto.fi