The Japanese oyster (Crassostrea gigas) has been introduced in France on a large scale to replace cultivation of the Portuguese oyster (Crassostrea angulata), affected by a viral disease. The importation took place from 1971 ta 1975, with broodstock coming from British Columbia (Canada) and spat from Japan. Good growth rate and success of the natural setting on the French Atlantic coast attested to the success ofthis implantation, with a production which oeached 80000 t by 1976. The precautionary measures associated with this transfer limited the implantation of an introduced fauna, 15 years after, to: Balanus amphitrite, Aiptasia pulchella and, on the Mediterranean coast, Undaria pinnatifida and Laminaria japonica. The authors also discuss the possible role of Crassostrea gigas in spreading the viral disease. L'huître japonaise (Crassostrea gigas) a été introduite massivement en France dans le but de subvenir au remplacement de l'élevage de l'huître portugaise (Crassostrea angulata) décimée par une maladie virale. Ces importations effectuées de 1971 à 1975 concernent des géniteurs provenant de Colombie Britannique (Canada) et du naissain en provenance du Japon. De bonnes performances de croissance et le succès du captage sur la côte atlantique française traduisent la réussite de l'implantation de cette espèce dont la production a atteint, dès 1976, 80000 tonnes. Les précautîons associées à cette importation ont permis de limiter l'implantation d'une faune associée dont les principales espèces, 15 ans après, sont: Balanus amphitrite, Aiptasia pulchella et, sur la côte méditerranéenne, Undaria pinnatifida et Laminaria japonica. Enfin est discuté le rôle possible de Crassostrea gigas dans la propagation de la maladie à virus.

Patterns of mitochondrial DNA (mtDNA) variation were used to analyse the population genetic structure of southwestern Indian Ocean green turtle (Chelonia mydas) populations. Analysis of sequence variation over 396 bp of the mtDNA control region revealed seven haplotypes among 288 individuals from 10 nesting sites in the Southwest Indian Ocean. This is the first time that Atlantic Ocean haplotypes have been recorded among any Indo-Pacific nesting populations. Previous studies indicated that the Cape of Good Hope was a major biogeographical barrier between the Atlantic and Indian Oceans because evidence for gene flow in the last 1.5 million years has yet to emerge. This study, by sampling localities adjacent to this barrier, demonstrates that recent gene flow has occurred from the Atlantic Ocean into the Indian Ocean via the Cape of Good Hope. We also found compelling genetic evidence that green turtles nesting at the rookeries of the South Mozambique Channel (SMC) and those nesting in the North Mozambique Channel (NMC) belong to separate genetic stocks. Furthermore, the SMC could be subdivided in two different genetic stocks, one in Europa and the other one in Juan de Nova. We suggest that this particular genetic pattern along the Mozambique Channel is attributable to a recent colonization from the Atlantic Ocean and is maintained by oceanic conditions in the northern and southern Mozambique Channel that influence early stages in the green turtle life cycle.

The green turtle Chelonia mydas is classified as endangered because of global declines over the past few centuries due to human exploitation and habitat destruction, particularly the loss of nesting areas. We used the number of tracks as an indicator of breeding female abundance at their nesting sites to study the seasonality and trends of turtles breeding at 3 islands in the SW Indian Ocean: Europa, Tromelin and Grande Glorieuse, over 20 yr. On Tromelin, tracks were counted along the entire nesting beach, but on Europa and Grande Glorieuse counts were limited to a proportion of the island. Europa and Tromelin exhibited similar seasonal patterns, with a well-defined peak during the wet season (November-February), compared to a dry season peak for Grande Glorieuse (March-June). The main season was significantly longer on Grande Glorieuse (288 ± 43 d) than on Europa (218 ± 60 d), with Tromelin intermediate (252 ± 43 d). There was greater variation in the start of a season compared to the median and end at all sites throughout the study. Approximately 7178 ± 3053 (n = 19) tracks were recorded annually on the entire nesting beach on Tromelin, compared with 1480 ± 666 (n = 19) on 16% of nesting beaches on Grande Glorieuse and 1361 ± 903 (n = 23) on 26% of beaches on Europa. The number of tracks has increased significantly on Europa (3% yr -1 ) and Grande Glorieuse (6% yr -1 ). The increasing number of nesting turtles illustrates the effectiveness of conservation measures on sites formerly exploited by humans.

ABSTRACT. A branchial infection of Pecten maximus is histologically and ultrastructurally described. Gill epithelia1 cells were heavily infected with colonies of procaryotes, believed to belong to the Rickettsiales.In March 1987, a mass mortality (ca 40 O/O) of Pecten maximus from St Brieuc, N Brittany, France, was reported. Collections were made at this site in order to conduct an anatomopathological study, which revealed a procaryotic infection of gill endothelial cells.Materials and Methods. Adult and juvenile scallops were collected by dredging at St Brieuc. Tissues were fixed either in Carson's fixative for light microscopy or in glutaraldehyde 1.25 %/paraformaldehyde 2 % in 0.1 M sodium cacodylate/HCl buffer pH 7.4, followed by 1 % osmium tetraoxide in the same buffer, for transmission electron microscopy (TEM). Osmolarity was raised to 1100 mosm with sucrose (primary fixative) or with sodium chloride (secondary fixative). For light microscopy, samples of gills, digestive gland, mantle, kidney and muscle of a first set of 25 individuals were processed and embedded in paraffin; 3 pm sections were stained with hematoxylin and eosin. A second set of 50 individuals was treated as above except that only gills and digestive gland were examined.For TEM, gill tissues were prepared using an automatic processor and embedded in LX 112. Sections (60 to 90 nm) were contrasted with lead citrate and aqueous uranyl acetate by means of the LKB Ultrostainer. Grids were examined with a Jeol 1200 CX electron microscope.

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