"In marine ecology there is an urgent need to understand the functioning of the lower part of the pelagic food web, its response to and effect on climate change, its response to pollution and environmental toxins, and its role in producing food for commercially important species at higher trophic level. This requires access for European scientists to tools allowing experimental approaches to near-natural pelagic systems. To meet this need, we propose a network (MESOAQUA) of European marine mesocosm facilities. MESOAQUA will: - Offer European researchers access to a range of mesocosm facilities in contrasting environments. - Develop and test new technologies that allow access to off-shore environments - Improve the services of the facilities by exchange of technology and experience - Facilitate cross-disciplinary fertilisation and a better coordination of mesocosm research - Promote the training of young scientists in the use of experimental ecosystem research MESOAQUA is necessary because: - System level experimentation is required to understand and predict the responses of the pelagic ecosystem in changing ocean subject to increasing anthropogenic pressure. - There is no present system for trans-national access to such experiemental facilities, particularly not to facilities offering access to different water masses - There is no present technology allowing mesocosm experiments in open waters"