Impact of temperature on larval development and evolution of physiological indices in Crassostrea gigas

The effect of four temperatures, ranging between 17 °C and 32 °C, was studied on development and lipid reserve management of Crassostrea gigas larvae. No effect of temperature was found on larval mortality, as high survival (> 90%) was recorded before competence at all temperatures studied. Temperature did, nonetheless, have a strong effect on growth and settlement success. At low temperature (17 °C), larvae competent to metamorphose were only observed from day 23 and only a low percentage finally achieved metamorphosis (12%). The opposite was seen at temperatures ≥ 27 °C: larval competence appeared at day 18 and led to high rates of metamorphosis (60–90%). This difference at settlement seemed to be linked to larval growth, which showed rates of 7 μm d− 1 at 17 °C vs. 10.5 μm d− 1 at 32 °C. In addition, a higher accumulation of lipid reserves at low temperature was revealed by both biochemical (TAG/ST) and colorimetric (OLI) methods. In fact, the lower the temperature, the higher the mean TAG/ST levels recorded (6–9 at 17 °C vs. 2–4 at 32 °C). In the same way, larvae reared at 17 °C had a percentage lipid surface coverage between 19 and 29% (at sizes between 80 and 230 μm), while lipids covered only 5 to 16% of the surface of larvae reared at 32 °C (at size < 250 μm). Neither of these physiological indices can, however, provide a relevant indication of the larval performance induced by different rearing temperatures.