Effect of starvation on physiological and survival traits of Mimachlamys varia (Linneaus, 1758)

In order to better understand Mimachlamys varia (Linneaus, 1758) response to nutritional stress, a controlledcondition experiment was conducted. Two scallop batches (i.e. juveniles and adults) were completely fooddeprived for 3 months. Changes in mass and energy content of tissues (adductor muscle, digestive gland, rest of the soft tissues), as well as stable carbon and nitrogen isotope ratios of the adductor muscle were monitored weekly. Both batches exhibited a 3-phase response to starvation. For adults, phase 1, was characterized by a fast loss in mass, an delta 15N-enrichment, a stable calorific power, and a low mortality, corresponding to a transitional stage associated with protein-storage consumption. Phase 2 (day 28-42) exhibited a stabilization of mass and delta 15N values, coinciding with a digestive gland calorific power drop and an acceleration in mortality. This corresponds to a "protein sparing" stage where highly energetic fuel such as lipids, which are stored especially in the digestive gland in pectinids, are consumed in priority. Juveniles exhibited a distinct response characterized by a significant mass loss and an increase in calorific power during the first phase (day 0-28). This body weight decrease may involve the remobilization of low-caloric biochemical compounds (e.g. proteins) using the structure as internal fuel, thus limiting somatic maintenance costs. During the second month, body mass and calorific power stabilized, indicating a "protein sparing" stage. In a third phase for both age classes, mass decreased again together with a sharp increase in mortality: essential structure was ultimately remobilized. The survival rate of juveniles was higher than that of adults during the first two months of the experiment (97% and 64%, respectively). Although the time required for starvation to deplete of half the cohort is higher for juveniles than for mature individuals, increase in mortality rate after reaching the "Point of No Return", (e.g. the beginning of the last phase) was higher in juveniles than in adults. These results highlight the potential impacts of starvation at the population level, beyond the direct impact on individual survival. For instance, individuals may not effectively contribute to reproduction during the spawning period if exposed to a prolonged winter starvation episode. In particular, since highly energetic compounds stored in the digestive gland are often used as fuel to initiate gametogenesis in pectinids. Similarly, decrease in somatic weight in juveniles may delay their sexual maturity and hence their ability to contribute to population reproductive potential.