Vibrio harveyi is a marine bacterial pathogen responsible for episodic abalone epidemics associated with massive mortalities in France, Japan, and Australia. The aim of this study was the understanding of a possible role of the p38 MAPK in abalone haemocyte responses towards this bacterium. First, the pathogenicity of different V. harveyi strains was compared in both immersion and injection trials, and clear differences were detected. The three strains, ORM4, 04/092, and 05/053, all isolated from moribund abalone, induced up to 80% mortalities in immersion or injection challenges (LD(50) (ORM4) = 2.5 x 10(2) CFU animal(-1)). The two strains, LMG 4044T and LMG 7890 were non-pathogenic towards abalone in immersion trials, and needed very high numbers for killing by intramuscular injections (LD(50) = 8.9 x 10(4) and 1.6 x 10(5) CFU animal(-1), respectively). To start unraveling the mechanism explaining these differences, the p38-MAPK, a keyplayer in antimicrobial immune response, was studied. The non-pathogenic strain, LMG 7890 can be eliminated by abalone haemocytes and induces haemocyte phagocytosis and high ROS production. With different concentrations of a p38-specific inhibitor, SB203580, p38 implication was shown. This inhibitor reduced phagocytosis and ROS induction leading to LMG 7890 proliferation. In the case of the pathogenic ORM4 which can not be eliminated by abalone haemocytes, no phagocytosis and ROS production was induced, and a retarded p38 activation was observed. Taken together, our results suggest that p38 MAPK modulation may be one of the ways of virulent V. harveyi to attack its host and escape abalone immune response.

The objective of this study was to optimise the rearing of the sea urchin Paracentrotus lividus (Lamarck, 1816) larvae through the choice of an optimal diet. The effects on larvae reared in oyster facilities and using different microalgae species were analysed. Four experimental diets were tested: 1) Isochrysis aff. galbana (Clone T-ISO), 2) Dunaliella tertiolecta, 3) Rhodomonas sp. and 4) a combined diet of these three species (1:1:1). The biometrics of larvae were carried out every two days. Post-larval survival was assessed when competence for settlement was achieved. Induction of settlement was carried out by contact between larvae and oyster shell particles. This method, adapted from oyster farming, was used for the first time in sea urchin culture. After 9 days post-settlement, metamorphosed juveniles were sampled and post-settlement survival was assessed. The biochemical composition (proteins, carbohydrates, lipids) of microalgae and larvae was measured.