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Estimation of physical and physiological performances of blacklip pearl oyster larvae in view of DEB modeling and recruitment assessment
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International audience. In French Polynesia black pearl farming represents one of the dominant business sectors. However, it still entirely relies on unpredictable Pinctada margaritifera spat collection success, which is itself conditioned by larval development completion. To assess the relationship between larval development and recruitment success, we studied under controlled conditions the effect of food concentration on development, growth, ingestion rate, survival and metabolic rate at the larval stage. Larvae were exposed to four different phytoplankton densities (2,5; 7,5; 15 and 30 cell.mu L-1). Larvae survived equally all over the range of phytoplankton concentration with an average survival rate of 16% at the end of experiments. Food concentration significantly affected the larval physiology throughout its development from birth to metamorphosis. Growth and feeding were close to those reported by previous laboratory observations with young spat of 210 mu m long obtained in 18 days of rearing at 28 degrees C for the highest food concentration. Differences in length at metamorphosis and cumulated energy ingested until settlement occurred according to trophic levels with a saturation threshold close to 0.0086 J.ind(-1). This level was reached at the food concentration of 15 cell.mu L-1. Larval development stages could be divided on the basis of the energy balance between feeding and respiration rates. An initial mixotrophic period with a lower and constant ingestion/respiration ratio over the first three days (from birth to D-veliger larva) was followed by an exotrophic phase characterized by a sharp increase in energy balance highly dependent of food concentration. Finally two sharp decreases of feeding rates were recorded during metamorphosis before umbonate and eyed stages. This study provided numerous new clues to establish a quasi-deterministic relationship between food condition and larval development. It highlights the major effect of food concentration and how energy intake through feeding as well as behavioral and physiological transitions can optimize larval development duration and minimize "the risky phase" of their life cycle. By taking into account the observed metabolic switches, the results provide a strong foundation for Dynamic Energy Budget model development and better description of the complex interactions between P. margaritifera physiology and environmental conditions.
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