Thermal dependence of clearance and metabolic rates in slow- and fast-growing spats of manila clam Ruditapes philippinarum

Abstract

Thermal dependence of clearance rate (CR: lh(-1)), standard (SMR: Jh(-1)) and routine metabolic rates (RMR: Jh(-1)), were analyzed in fast (F)- and slow (S)-growing juveniles of the clam Ruditapes philippinarum. Physiological rates were measured at the maintenance temperature (17°C), and compared with measurements performed at 10 and 24°C after 16h and 14days to analyze acute and acclimated responses, respectively. Metabolic rates (both RMR and SMR) differed significantly between F and S seeds, irrespective of temperature. Mass-specific CRs were not different for F and S seeds but were significantly higher in F clams for rates standardized according to allometric size-scaling rules. Acute thermal dependency of CR was equal for F and S clams: mean Q 10 were ≈3 and 2 in temperature ranges of 10-17 and 17-24°C, respectively. CR did not change after 2weeks of acclimation to temperatures. Acute thermal effects on SMR were similar in both groups (Q 10≈1 and 1.6 in temperature ranges of 10-17 and 17-24°C, respectively). Large differences between groups were found in the acute thermal dependence of RMR: Q 10 in F clams (≈1.2 and 1.9 at temperature ranges of 10-17 and 17-24°C, respectively) were similar to those found for SMR (Q 10=1.0 and 1.7). In contrast, RMR of S clams exhibited maximum thermal dependence (Q 10=3.1) at 10-17°C and become depressed at higher temperatures (Q 10=0.9 at 17-24°C). A recovery of RMR in S clams was recorded upon acclimation to 24°C. Contrasting metabolic patterns between fast and slow growers are interpreted as a consequence of differential thermal sensitivity of the fraction of metabolism associated to food processing and assimilation.