This volume on the ecology of Mauritanian coastal waters and in particular the Banc d'Arguin, allows us to understand the functioning of this remarkable coastal wetland. Major questions concern the interaction between the Banc d'Arguin ecosystem on the one hand and the adjoining systems of the open ocean with its intensive upwelling phenomena and the Sahara desert on the other. Is the Banc d'Arguin ecosystem relatively isolated from its surroundings and does it function as a tropical pocket in a more temperate surrounding, as suggested by Sevrin-Reyssac (1983); or does it interact with both the Sahara and the Atlantic Ocean? At the Banc d'Arguin, the area between the estuarine parts and the open ocean is extremely shallow and largely uncharted. Large research vessels cannot penetrate the shallows, whereas small vessels are often unable to negotiate the outer part of the shallow area due to rough weather conditions. Hence, separate teams report on work at the seaward side of this shallow sill and at the landward side.