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<p>Shellfish and seaweed aquaculture substantially influence marine carbon sinks. However, comprehensive comparisons and analyses of dissolved inorganic carbon (DIC) uptake, dissolved organic carbon (DOC) release, and CO<sub>2</sub> source-sink dynamics under both monoculture and coculture regimes remain limited. This study utilized a custom-built closed system to monitor CO<sub>2</sub> in the water and air, and the dynamics of seawater DIC, DOC, and overlying atmospheric CO<sub>2</sub> concentrations in mono- and co-cultures of seaweed (<i>Gracilaria lemaneiformis</i>) and oysters (<i>Crassostrea gigas</i>). The monoculture of <i>G. lemaneiformis</i> apparently demonstrated significant carbon sequestration capacity, effectively reducing both seawater DIC and overlying atmospheric CO<sub>2</sub> concentrations. The absorption rates were 0.026 mg/(g h) for atmospheric CO<sub>2</sub> and 1.081 mg/(g h) for seawater DIC (both calculated as CO<sub>2</sub> equivalent). In contrast, oyster monoculture had minimal impact on seawater DIC but significantly elevated overlying atmospheric CO<sub>2</sub> levels, functioning as a CO<sub>2</sub> source with a release rate of 0.110 mg/(g d). Notably, in <i>G. lemaneiformis</i>–oyster cocultures, the system not only reduced seawater DIC concentrations—often more effectively than <i>G. lemaneiformis</i> monoculture alone—but also substantially mitigated the CO<sub>2</sub> release associated with oysters. Furthermore, cocultures with a high <i>G. lemaneiformis</i>-to-oyster ratio facilitated a net shift from CO<sub>2</sub> emission to sequestration. At a <i>G. lemaneiformis</i>-to-oyster weight ratio of 1:8, the water-air CO<sub>2</sub> exchange approached equilibrium. Regarding organic carbon, DOC release rates also differed significantly among the three cultivation modes. <i>G. lemaneiformis</i> monoculture produced a notably higher DOC release rate than oyster monoculture, while their coculture exhibited an approximately additive effect on DOC release. Furthermore, the photosynthetic activity of <i>G. lemaneiformis</i> was highly responsive to light-dark cycles. During the light phase, seawater pH, dissolved oxygen, and DOC levels increased, while DIC concentrations decreased; these trends reversed during the dark phase. Among these parameters, pH was identified as a critical environmental factor regulating seawater partial pressure of CO<sub>2</sub> and, consequently, the water-air CO<sub>2</sub> exchange. These findings provide valuable insights and a robust scientific basis for assessing the carbon source-sink dynamics of shellfish and seaweed aquaculture systems.</p>

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Carbon absorption, release, and their impact on water-air CO2 exchange in seaweed and shellfish coculture

  • 期刊论文

  • 发表日期：

    2026年3月16日

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  • Kunxian Tang,
  • Bowen Huang,
  • Yongyu Zhang,
  • Yong Ma,
  • Xiaoqiong Wei,
  • Chenyan Liu,
  • Jiawei Chen,
  • Heyang Li,
  • Fei Zhang

摘要

Shellfish and seaweed aquaculture substantially influence marine carbon sinks. However, comprehensive comparisons and analyses of dissolved inorganic carbon (DIC) uptake, dissolved organic carbon (DOC) release, and CO2 source-sink dynamics under both monoculture and coculture regimes remain limited. This study utilized a custom-built closed system to monitor CO2 in the water and air, and the dynamics of seawater DIC, DOC, and overlying atmospheric CO2 concentrations in mono- and co-cultures of seaweed (Gracilaria lemaneiformis) and oysters (Crassostrea gigas). The monoculture of G. lemaneiformis apparently demonstrated significant carbon sequestration capacity, effectively reducing both seawater DIC and overlying atmospheric CO2 concentrations. The absorption rates were 0.026 mg/(g h) for atmospheric CO2 and 1.081 mg/(g h) for seawater DIC (both calculated as CO2 equivalent). In contrast, oyster monoculture had minimal impact on seawater DIC but significantly elevated overlying atmospheric CO2 levels, functioning as a CO2 source with a release rate of 0.110 mg/(g d). Notably, in G. lemaneiformis–oyster cocultures, the system not only reduced seawater DIC concentrations—often more effectively than G. lemaneiformis monoculture alone—but also substantially mitigated the CO2 release associated with oysters. Furthermore, cocultures with a high G. lemaneiformis-to-oyster ratio facilitated a net shift from CO2 emission to sequestration. At a G. lemaneiformis-to-oyster weight ratio of 1:8, the water-air CO2 exchange approached equilibrium. Regarding organic carbon, DOC release rates also differed significantly among the three cultivation modes. G. lemaneiformis monoculture produced a notably higher DOC release rate than oyster monoculture, while their coculture exhibited an approximately additive effect on DOC release. Furthermore, the photosynthetic activity of G. lemaneiformis was highly responsive to light-dark cycles. During the light phase, seawater pH, dissolved oxygen, and DOC levels increased, while DIC concentrations decreased; these trends reversed during the dark phase. Among these parameters, pH was identified as a critical environmental factor regulating seawater partial pressure of CO2 and, consequently, the water-air CO2 exchange. These findings provide valuable insights and a robust scientific basis for assessing the carbon source-sink dynamics of shellfish and seaweed aquaculture systems.