Growth of the mussel, Mytilus edulis, was compared for the first time under three culture regimes, longline located in open sea, pole and on-bottom both situated on an intertidal flat, in the Pertuis Breton, on the Atlantic coastline of France. Mussel sampling was performed on a monthly basis over 1 year while monitoring of hydrobiological parameters was conducted on a biweekly basis. Fluctuation of environmental parameters showed a similar pattern on both sea and shore locations with generally higher concentration levels for the intertidal area compared with the open sea, i.e. 4.07 and 3.17 mg 1(-1) for particulate organic matter, 3.16 and 2 mug 1(-1) for chlorophyll-a, 58.43 and 38.72 mg 1(-1) for inorganic-N, respectively. A clear seasonal growth pattern was observed, being similar for all three cultural conditions. A gradient of length and weight growth appeared as a function of the culture type. Longline mussels exhibited the highest performance while Bottom-type culture showed the lowest. An emersion time of approximately 26% was estimated from the temperature record of the Pole station during the period of maximal growth. This could partly explain the reduced growth in length on Pole compared to Longline. While growth was faster in Longline culture and condition index were better for Pole culture, further data on the carrying capacity of the area are needed for the establishment of a mussel culture extension policy.