DAO prepress abstract  -  doi: 10.3354/dao01897

ABSTRACT: We examined the original manuscripts of a French national survey conducted in 1933 on the state of Zostera marina beds along the French coasts during the ‘wasting disease’ of the early 1930s, which struck the entire North Atlantic population. Based on GIS related techniques and on old aerial photograph set, we present the first accurate mapping of the Z. marina beds before the ‘wasting disease’ and assess their spatial recolonization since the 1950s in the Chausey archipelago (France), hosting large Z. marina beds. The national survey confirmed that the Z. marina beds almost totally disappeared from the French coasts mainly from the beginning of the 1930s. However, the disease symptoms seem to have begun locally a few years before. On the study site, we found that the Z. marina beds were more than twice as extended than as they are today, and covered both subtidal and intertidal areas. 20 years after the disease (1950s), they had hardly recolonized, and contrary to the recolonization patterns reported elsewhere in Europe, they were mainly restricted to subtidal areas. The subtidal and intertidal Z. marina beds of the site are currently rapidly expanding.