Geographic Variation in Morphology and Physiology of Meretrix meretrix (Linnaeus, 1758) Along the Chinese Coast

The clam Meretrix meretrix (Linnaeus, 1758) is a commercially significant bivalve species widely distributed along China's coast. To investigate the differences among geoducks from different geographic populations, this study investigated the geographical variations in morphology and key physiological traits among three populations spanning a latitudinal gradient: Liaoning Dandong (north), Jiangsu Rudong (center), and Guangxi Qinzhou (south). We analyzed nine morphological traits and measured physiological indicators-including filtration rate, feeding rate, oxygen consumption, ammonia excretion, and burrowing behavior-at two temperatures (18 °C and 20 °C). The results revealed significant morphological differentiation among the populations. Physiologically, the Guangxi population demonstrated superior adaptation to warmer conditions, exhibiting the highest feeding and metabolic rates at 20 °C. In contrast, the Liaoning population performed better at the lower temperature of 18 °C, while the Jiangsu population showed intermediate characteristics. Furthermore, burrowing capacity varied significantly, with the southern population having the highest burrowing rate. These findings demonstrate clear population-specific adaptations to local thermal environments, likely driven by long-term acclimatization. This study provides a crucial scientific basis for the conservation of genetic resources and informs regionalized aquaculture strategies for M. meretrix, emphasizing the importance of selecting locally adapted populations for cultivation.