Environmental and metabolic influences on daily to hourly element/Cashell of Tridacna derasa cultured under elevated Ba2+ background concentration conditions

Abstract

Tridacna spp. has been demonstrated to be ideal for paleoclimate study. Some element/Ca_shell ratios of Tridacna, such as daily Fe/Ca_shell and Mn/Ca_shell have been identified as potential proxies in tropical cyclone reconstructions. However, the environmental implications of daily to hourly Ba/Ca_shell, Sr/Ca_shell, and Mg/Ca_shell remain ambiguous due to the complexity of the combined effects of environment and physiology on growth. Here, a laboratory culture experiment was carried out to explore the factors that affect the element/Ca_shell of the inner and outer layers of the Tridacna T1 specimen, as well as the incorporation mechanism of the Ba²⁺, Sr²⁺, and Mg²⁺ into the inner shell layer. The results showed that the daily to hourly Ba/Ca_shell of the inner and outer layers could respond to the input of exogenous Ba²⁺ in the background seawater. The ion-transport mode for Ba²⁺ and Sr²⁺ may be different in the inner layer (intercellular transport) and outer layer (intracellular transport) due to the different metabolic activity. Ba/Ca_shell of the inner layer was significantly positively correlated with Ba/Ca_water (r = 0.37, p < 0.01), and significantly negatively correlated with water temperature after detrended (r = −0.45, p < 0.001). Under high Ba/Ca_water level (45 times more than natural seawater), the incorporation ability of Ba²⁺ into the inner shell layer probably be improved, Ba²⁺ appears to incorporate synchronously with Sr²⁺, which may result in a significant positive correlation between Ba/Ca_shell and Sr/Ca_shell (r = 0.78, p < 0.001). This synchronous incorporation likely disrupted the expected relationship between Sr/Ca_shell and water temperature, rendering it insignificant. Additionally, Mg²⁺ incorporation into the inner shell layer might appear to follow an independent mechanism, distinct from those of Ba²⁺ and Sr²⁺.