Evalution du bilan énergétique de l'huître creuse, Crassostrea gigas, en baie de Marennes-Oléron (France)

This ecophysiological study was conducted on the Japanese oyster (Crassostrea gigas) reared in Marennes-Oléron bay (France), in May 1992. Measurements were achieved using natural food conditions on three different days (a, b, c) at different tide levels (coefficient of 49, 57, and 88). Total particulate matter was continuously monitored with a micro-computer and a turbidimeter probe. The "consumption" function was calculated using a new formula allowing for particulate leakage prior to the pre-ingestive particle sorting. This particle leakage represents a passive loss of particles flowing through the branchial filter. Comparisons of the consumption and absorption rates of organic matter and chlorophyll a showed significant differences between seston availabilities of 55 mg.1-l (e) and less than 30 mg.1-' seston load (a, b). Comparisons of the selection efficiency and absorption rate of the chlorophyll a, (43.3 and 81.6%), respectively, and total organic matter (33.4 and 68.7%), respectively, demonstrated the oysters' capacity to sort out organic matter. The energy budget was calculated using chlorophyll a and total organic matter. The estimated scope for growth of 0.88-11.60 and 47.60 J.h-'.g-' for the conditions 13.5-28.9 and 54.6 rng.1-l seston load respectively (a, b, c), illustrated the large daily variability in available energy allocated to organic production in the wild. These results were consistent with the growth data of cultured oysters in Marennes-Oléron bay.