Effects of temperature on physiological energetics and carbon budget of Saccostrea malabonensis

Saccostrea malabonensis, a dominant species in tropical high-salinity oyster reefs, is often exposed to drastic temperature and frequent temperature fluctuations. To investigate the effects of temperature variations on the carbon budget capacity and potential ecological carbon sink function of S. malabonensis, five temperature gradients (18, 22, 26, 30, and 34 ℃) were established. Key physiological parameters were measured at each temperature, and the corresponding energy and carbon budget models were constructed. Among them, the filtration rate, ingestion rate, and oxygen consumption rate showed no significant difference between 30 and 34 ℃ groups (p>0.05), but were significantly higher than those in lower temperature treatment groups, specifically 18, 22, and 26 ℃ groups (p<0.05); the fecal pellet production rate at 34 ℃ was significantly higher than that in other temperature treatment groups (p<0.05); except for 26 and 34 ℃ groups, there was no significant difference in ammonia excretion rate among temperature treatment groups (p>0.05). Assimilation efficiency increased first and then decreased with temperature, reaching a peak at 30 ℃ (59.01%), and was significantly higher than that in 18 and 22 ℃ groups (p<0.05); the oxygen-nitrogen ratio (O/N) in the 26, 30, and 34 ℃ treatment groups (20.49–24.62) was significantly higher than that in 18 and 22 ℃ groups (9.18–13.85) (p<0.05). In terms of energy allocation, except for 30 ℃ groups, all treatment groups showed that fecal energy accounted for the largest proportion (40.53%–72.19%), followed by growth energy (21.61%–55.94%), with excretion energy accounting for the smallest proportion (0.21%–0.90%). Carbon budget results showed that fecal carbon increased with rising temperature, while growth carbon was highest at 30 ℃ (1.94 mg·g⁻¹·h⁻¹). The proportions of carbon budget components varied in a pattern similar to energy allocation: the proportion of fecal carbon first decreased and then increased, while the proportion of growth carbon showed the opposite trend. This study shows that 30 ℃ is the optimal temperature for S. malabonensis, at which the species can achieve the most stable metabolism, effective individual growth, and maximal carbon fixation potential.