THE DISTRIBUTION OF THE BARNACLE ELMINIUS MODESTUS DARWIN IN FRANCE

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Abstract
SUMMARY: The distribution of Elminius modestus along the coast of France may be divided into four sectors. From the Belgian frontier to Cap de la Hague, it is ubiquitous both on the coast and in harbours wherever suitable surfaces for settlement exist. From Cap de la Hague to the Trieux estuary, it is scarce or absent. From the Jaudy to the Rade de Brest, it is plentiful in all sheltered estuaries but scarce on the open coast. South of the Rade de Brest, only isolated individuals have been met in a few estuaries, the furthest afield being at St. Jean‐de‐Luz close to the Spanish frontier. The distribution on the Channel coast of France resembles closely that on the coast of southern England It is suggested that the tidal races and the absence of large bodies of sheltered water form a barrier to its westward spread both at Portland Bill and at Cap de la Hague Conditions in the Gulf of St. Malo, unlike those in Lyme Bay, are probably not directly unfavourable to the growth and development of individuals, but are probably unfavourable for the initial establishment of a population on account of the large tides that occur there. These may sweep locally developing populations of larvae out of the river systems and so disperse them too widely for reproduction to be possible. The Brittany population and that of the eastern part of the Channel must have been established independently. Both are now fairly stable and well established The Brittany population is most likely to have been disseminated from the Rade de Brest; that east of Cap de la Hague either from Cherbourg or more likely from Le Havre, Trouville and the Seine estuary, perhaps at or soon after the Allied invasion in 1944 The populations in Holland and France, though now continuous: probably arose independently. The two populations probably merged on the coast of Belgium approximately in 1949–1950