Cardiac performance: a thermal tolerance indicator in scallops

Abstract

Thermal tolerance has become an active research area in marine poikilotherms due to the influence of increased sea temperature caused by global warming. Previous indicators of thermal tolerance in bivalves are generally laborious and time-consuming and even require killing the specimens. In this study, we demonstrated that heart rate (HR) was a stable and reliable indicator for scallop physiological status by applying an infrared-based cardiac performance monitoring system. The feasibility of HR-based Arrhenius break temperatures (ABTs) as a scallop thermal tolerance indicator was evaluated by investigating ABTs of four species with different thermal limits, including the Yesso scallop (Patinopecten yessoensis), the Zhikong scallop (Chlamys farreri), the bay scallop (Argopecten irradians), and the Catarina scallop (Argopecten ventricosus). In accordance with the thermal limits, ABTs of the Yesso scallop, Zhikong scallop, bay scallop, and Catarina scallop were 22.03 ± 0.19, 29.10 ± 0.25, 32.20 ± 0.25, and 34.09 ± 0.19 °C, respectively, suggesting that the ABT could indicate thermal limits in interspecific scallops. Variations in the ABTs were observed among intraspecific scallops with different sizes, weights, and ages, suggesting that smaller and younger scallops tend to have higher thermal limits. Significant differences in ABT were also observed between pre- and post-spawning individuals, implying that spawning behavior could decrease scallop thermal limits. The above results suggest that HR-based ABT can detect not only interspecific but also intraspecific thermal tolerance in scallops. This study reports the feasibility of infrared-based cardiac performance as a rapid, efficient, and noninvasive indicator for bivalve thermal tolerance.