Expansion of the red alga Grateloupia doryphora along the coasts of Brittany (France)

Grateloupia doryphora (Montagne) Howe (Halymeniales, Halymeniaceae) has pre viously been reported for two locations along the Brittany coastline (Franc e). Important ecological and morphological traits of the species in the bre ton populations are detailed here. Because of the impressive size it can re ach, G. doryphora can be considered as the largest red alga in the world. G . doryphora has the tendency to dominate the algal flora once installed. At Lorient, in addition to the marginal extension of the population, a progre ssive colonisation of the whole intertidal zone has been noted for 2 years. The species actually preferentially develops in currents and pools where i t is abundant between early winter and mid summer. An interesting developme nt is the recent spreading from the mid and lower eulittoral towards the up per rocky pools. The seasonality of the life-cycle has also been studied ov er 2 years. In addition, this work reports on the first identification of G . doryphora near the Loire estuary in South Brittany, at Concarneau and in the Bay of Brest in western Brittany, and on the coasts of Normandy, at Gra nville and Cherbourg. The occurrence of attached specimens on ship hulls an d pontoons suggests a distant transport of the species by navigation. Consi dering the rapid geographical propagation of G. doryphora, and its tendancy to proliferate in settling locations, the species can be regarded as poten tially invasive on the north-west coasts of Europe.