9 The French Atlantic Coasts
P. DION and S. LE BOZEC
9.1 Introduction
Summer mass blooms of macroalgae have been occurring increasingly
for two decades along the French Atlantic coastline (Fig. 9.1). The coasts
of Brittany are the most affected, considering the nearly 100000 m 3 of
green seaweeds collected yearly from the beaches. One member of the
genus Ulva is particularly involved in these mass blooms, although some
ectocarpales, for example Pilayella littoralis, recently appeared in some
localities.
The enclosed Bay of Arcachon is the second most affected area with
about 6000 m 3 of green algae removed yearly. Eutrophication also occurs,
at least as a natural phenomenon, in the 30 000 ha of salt marshes of the
French Atlantic coast.
The present knowledge of the eutrophication mechanisms producing
the green tides on the Brittany coasts is presented here. Possible fighting
means (curative as well as preventive measures) are also reviewed.
9.2 Green Tides of the Brittany Coasts
The term "green tides" in Brittany generally refers to concentrations of
unattached forms of Ulva sp., occurring in summer in the nearshore
waters (Fig. 9.2), and leading locally to massive beaching (Fig. 9.3).
Green tides are not in themselves a hazard to human health, and a
negative impact of decomposing deposits on the ecosystem has not yet
CEVA (Centre d'Etude et de Valorisation des Algues), BP 3, 22610 Pleubian, France
Ecological Studies, VoL 123
Schramm/Nienhuis (eds) Marine Benthic Vegetation
© Springer-Verlag Berlin Heidelberg 1996