The south temperate and Antarctic ascidian Corella eumyota reported in two harbours in north-western France

Abstract

In July 2002 the southern hemisphere ascidian Corella eumyota was detected in the northern hemisphere for the first time, attached to floating docks in two harbours in north-western France: Perros-Guirec and Camaret-sur-Mer. Most individuals in the large clumps of tightly packed aggregations contained a clutch of brooded embryos in the atrial cavity, resting on the posterolateral epithelium overlying the ovotestis very close to the openings of the sperm duct and oviduct which are immediately adjacent to each other on the surface of the ovotestis, a morphological peculiarity not previously reported. These openings are far from the atrial siphon; it is possible that the species routinely self-fertilizes. The larvae are retained after hatching until they are competent to settle, resulting in a very short free-swimming larval period, limited dispersal, and a tendency for the larvae immediately after release to settle on the parent tunic or adjacent adults. It is hypothesized that individuals attached to some type of hard substrate were transported anthropogenically to France. Because the two harbours in which these nonindigenous ascidians were living are small, they probably represent secondary sites of invasion into France; the primary sites have not yet been identified.