The specific composition and distribution of zooplankton were examined during seven cruises along a transect line running offshore from Arcachon Basin (44-degrees 31'N). Copepods were the dominant zooplankters, followed in abundance by Cladocerans. The horizontal and vertical distribution of Copepods was studied in more detail. From the specific composition and the description of the variations in abundance of the taxa, two assemblages were determined. Some species of Copepods occurred only at the seaward stations (isobaths -130 m, -200 m). Conversely, most of the nearshore species had a distribution extending all over the continental shelf. Cladocerans and meroplanktonic larvae displayed a very coastal distribution (isobath -30 m). Samples were also taken in Arcachon Basin in order to estimate the tidal transport of zooplankton. It is mainly the nearshore species which enter the Basin. The extent of their penetration depends greatly on the depth distribution. Owing to the presence of a sill near the inlet, surface species were more strongly subjected to tidal exchanges. It appears that the exchanges of zooplankton between the coastal zone and Arcachon Basin are poor, especially for Copepods. Only the Cladocerans are transported regularly from the coastal zone to the entrance of Arcachon Basin.
