Phylogeography of the green turtle, Chelonia mydas, in the Southwest Indian Ocean.

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.

[Diseases of bivalve mollusks: risk and prevention]. / Les maladies des mollusques bivalves: risques et prévention.

The farming of shellfish, based on fishing and rearing in a natural environment, has developed considerably in recent years, particularly as a result of production of spat and juveniles in hatcheries and nurseries. The growing demand for trade in products, facilitated by modern means of transport, has increased the risks of disease spread. Using examples, the author analyses the risks incurred by shellfish farming methods and the risks linked to the present state of knowledge. Recommendations are made on prevention and the need for regulations, and difficulties encountered in this area are discussed. Finally, proposals are made to overcome the existing antagonism between marked demands and the need to protect shellfish farming.

[Some examples of introductions and transfers of mollusks]. / Quelques exemples d'introdutions et de transferts de mollusques.

Human beings have always introduced non-indigenous species into new environments. Such is the case with shellfish, which the Romans, fine connoisseurs, transferred from France to Italy to mature. The Pacific oyster (Crassostrea gigas) and the Manila clam (Ruditapes philippinarum) are among the most significant examples of these introductions. The author examines the causes, conditions, results, and economic and biological repercussions of these examples. The well known cases of the introduction and implantation of new populations of molluscs are relatively recent, dating back to the beginning of this century. These movements result from an intensification of fishing activities, and the development of the mollusc industry and of transportation. The introduction of fish has been attempted for hundreds of species, whereas the introduction of molluscs has involved no more than a few dozen recorded species. Finally, with regard to the deliberate introduction of molluscs, none has led to significant ecological disruption, but on the contrary, has led to the establishment of permanent coastal activities which do not greatly disturb the natural biotopes.

Evidence of neutralizing activity against T3 coliphage in oyster Crassostrea gigas hemolymph.

To investigate defense reactions of bivalve molluscs against viruses, experimental in vitro assays have been developed using T3 coliphage as a test virus. A native neutralizing factor in oyster Crassostrea gigas serum showed high individual variability and was enhanced significantly by repeated sampling of hemolymph from the same oysters. The responsible factor is apparently thermolabile and sensitive to EDTA treatment. Because of an inhibitory effect by the enzymatic inhibitor, phenylmethylsulphonyl fluoride (PMSF), the T3-neutralizing factor may be related to serine protease.

Separation of Crassostrea gigas hemocytes by density gradient centrifugation and counterflow centrifugal elutriation.

A protocol is described to separate several subpopulations of hemocytes in a unique medium which avoids cell aggregation and retains cell-viability. Isopycnic centrifugation in Percoll followed by counterflow centrifugal elutriation provides large quantities of separated granulocyte and hyalinocyte subpopulations.