A path towards appropriate degradation experiments for assessing carbon sequestration potential of macroalgae

The biodiversity and climate crises have increased the urgency to understand turnover rates and drivers of marine carbon sequestration. Efforts have concentrated on measuring degradation of macroalgae, to quantify how much of their carbon might be sequestered. We systematically reviewed literature on macroalgal degradation, compiling 364 measurements of exponential decay constant k. To date, most degradation experiments (1) are carried out in aquaria or shallow environments, (2) span short timescales, (3) use dried or frozen material, or (4) rarely incorporate environmental gradients driving degradation. Decay constants were higher in intertidal vs. subtidal habitats, for pre-treated algal tissue compared to fresh, and when refractory material was present rather than absent. These patterns have implications for estimates of export efficiency of macroalgal carbon to the deep ocean. Synthesis: We recommend that future studies of macroalgal degradation (1) adopt standardized approaches, such as using fresh material and litter bag mesh size of 10mm, to make studies more comparative, (2) measure degradation with sufficient frequency to robustly estimate decay constants and/or refractory material, and (3) incorporate environmental gradients, including depth, light and oxygen availability, to improve estimates of macroalgal carbon remineralisation rates during transport to deeper water.

生物多样性与气候危机加剧了人们理解海洋碳封存周转速率及其驱动因素的紧迫性。当前研究多聚焦于大型藻类（macroalgae）的降解过程，以量化其碳组分可被封存的比例。我们系统梳理了关于大型藻类降解的相关文献，共汇编得到364组指数衰减常数（exponential decay constant）k的实测数据。截至目前，多数降解实验存在以下四类局限：其一，实验多在水族箱或浅水环境中开展；其二，实验周期普遍较短；其三，实验材料多为干燥或冷冻样本；其四，极少纳入驱动降解过程的环境梯度变量。

研究结果显示，潮间带生境的衰减常数高于潮下带生境；经预处理的藻类组织的衰减常数高于新鲜样本；且当难降解物质存在时，衰减常数更高。上述模式对评估大型藻类碳向深海的输出效率具有重要参考意义。

综合分析：我们建议未来针对大型藻类降解的研究应遵循以下三项原则：其一，采用标准化实验方法，例如使用新鲜实验材料并采用10mm孔径的凋落袋（litter bag）网目尺寸，以提升不同研究间的可比性；其二，以足够高的观测频率开展降解速率测量，以稳健估算衰减常数及/或难降解物质占比；其三，纳入多维度环境梯度变量，包括水深、光照及溶氧可用性，以优化大型藻类碳向深水输送过程中的再矿化速率估算。