滤食性贝类贝壳总碳、有机碳含量及其降解速率初探

A Preliminary Study on the Total Carbon, Organic Carbon Content, and Degradation Rates of Shells in Filter-Feeding Shellfish

中文关键词: 滤食性贝类、海水养殖、贝壳有机碳、降解速率、碳汇

英文关键词: Filter feeding shellfish, Mariculture, Shell organic carbon, Degradation rate, Carbon sink

中文摘要:

      海水养殖滤食性贝类的贝壳碳含量占其总生物质碳的63.44～92.64%，在固碳和碳封存中的潜力成为研究热点，然而关于贝壳不同部位的碳含量及贝壳的碳封存效率尚不清晰。本文于 2022年9月在桑沟湾采集紫贻贝(Mytilus edulis)、栉孔扇贝(Chlamys farreri)、虾夷扇贝(Patinopecten yessoensis)、长牡蛎(Crassostrea gigas)、菲律宾蛤仔(Ruditapes phlippinarum)和毛蚶(Soapharca suberenata) 6种滤食性贝类，利用元素分析仪测定了贝壳不同部位(边缘、壳顶和整个贝壳)的总碳(Total carbon, TC)含量和有机碳(Total organic carbon, TOC)含量，通过室内自然降解法测定了贝壳总碳和有机碳降解速率。研究结果表明：(1) 不同种类贝壳中总碳和有机碳的含量不同，6种贝壳的总碳和有机碳含量范围分别为11.31%~13.37%和0.53%~2.17%，其中，紫贻贝总碳与有机碳含量均显著高于其他5种贝类，其余5种贝壳的总碳含量无显著性差异(P>0.05)，毛蚶有机碳含量显著高于其他4种贝类贝壳(P<0.05)。(2) 紫贻贝壳顶部的总碳与有机碳含量均显著低于壳边缘部分(P<0.05)；毛蚶壳顶部的有机碳含量显著低于壳边缘部分(P<0.05)，其余4种贝壳各部位间的总碳、有机碳含量差异不显著(P>0.05)。(3) 贝壳总碳和有机碳的降解速率因种类不同而不同，有机碳含量越高，总碳的降解速率越大。6种贝壳总碳降解速率k445在0.0219 a-1 ~ 0.0803 a-1之间， k445平均为0.05110.02 a-1。其中，毛蚶的总碳降解速率最大，菲律宾蛤仔的降解速率最小。贝壳有机碳降解速率k445在0.0329 a-1~0.6096 a-1之间，平均为0.16430.22 a-1。毛蚶的有机碳降解速率最大，牡蛎的降解速率最小。研究结果为评估我国海水养殖滤食性贝类的碳封存效应提供了数据支撑。

英文摘要:

      In the face of growing concerns over global climate change and carbon emissions, the study of marine carbon sinks has garnered significant attention. Filter-feeding bivalves, as a crucial group in coastal aquaculture ecosystems, play a substantial role in carbon sequestration by filtering particulate organic carbon (POC), such as phytoplankton and organic debris, during their growth processes. Additionally, they incorporate inorganic carbon into their shells, indirectly contributing to the enhancement of carbon sink functionality. The carbon content of bivalve shells in marine aquaculture accounts for 63.44% ~ 92.64% of their total biomass carbon. The degradation of organic matter and the rate of organic carbon breakdown within the shells are also key factors determining the potential for long-term carbon sequestration in the shells. However, little is known about the carbon content in different bivalve species and various parts of their shells. Thus, precise measurements of shell carbon content and insights into the kinetics of organic carbon degradation are crucial for further comprehending the carbon sequestration capacity of bivalves and evaluating the overall carbon sink potential of bivalve aquaculture. In this study, six species of filter-feeding bivalves were collected from Sanggou Bay in September 2022, including Mytilus edulis, Chlamys farreri, Patinopecten yessoensis, Crassostrea gigas, Ruditapes philippinarum, and Scapharca subcrenata. An elemental analyzer was employed to measure the total carbon content and organic carbon content in different parts of the shells (the edge, the umbo, and the entire shell). The total carbon and organic carbon degradation rates were determined through indoor natural degradation experiments. The results indicated that the total carbon and organic carbon content varied among different species. The range of total carbon content in the six species was from 11.31% to 13.37%, while the range for organic carbon content was from 0.53% to 2.17%. The total carbon and organic carbon content in M. edulis were significantly higher than in the other five species (P<0.05), with no significant difference in total carbon content among the remaining five species (P>0.05). Regarding organic carbon content, S. suberenata exhibited significantly higher value than the other four species, except for M. edulis (P<0.05). The total carbon and organic carbon content in the edge of M. edulis were significantly higher than at the umbo (P<0.05), while the organic carbon content in the edge of S. suberenata was also significantly higher than at the umbo (P<0.05). For the remaining four species, there was no significant difference in total carbon and organic carbon content between the edge and the umbo (P>0.05). The degradation rates of total carbon and organic carbon in the shells varied by species, with higher organic carbon content leading to a faster total carbon degradation rate. The total carbon degradation rates (k445) of the six types of shells ranged from 0.0219 a-1to 0.0803 a-1, with an average of 0.0511 ± 0.02 a-1. S. suberenata had the highest total carbon degradation rate (k445 = 0.0803 a-1), while R. phlippinarum had the lowest (k445 = 0.0219 a-1). Statistical analysis showed that the degradation rates of S. suberenata and M. edulis were significantly higher than the other four species (P<0.05). No significant difference in degradation rates was found among C. farreri, P. yessoensis and C. gigas (P>0.05), while R. phlippinarum had a significantly lower degradation rate than the other five species (P<0.05). The organic carbon degradation rates (k445) ranged from 0.0329 a-1 to 0.6096 a-1, with an average of 0.1643 ± 0.22 a-1. S. suberenata had the highest organic carbon degradation rate (k445 = 0.6096 a-1), while C. gigas had the lowest (k445 = 0.0329 a-1). Statistical analysis revealed that the degradation rate of S. suberenata was significantly higher than the other five species (P<0.05), with no significant difference between C. farreri and R. phlippinarum (P>0.05), or among M. edulis, P. yessoensis, and C. gigas (P>0.05). Except for S. suberenata, where the organic carbon degradation rate was significantly higher than the total carbon degradation rate (P<0.05), no significant difference was observed between total carbon and organic carbon degradation rates in the other species (P>0.05). As the world seeks to mitigate climate change by enhancing natural carbon sinks, shellfish aquaculture offers a promising pathway for carbon sequestration in marine ecosystems. Therefore, the determination of shell carbon content and the study of shell carbon degradation are critical approaches to understanding the carbon sink potential of shellfish farming. Filter-feeding shellfish not only achieve long-term carbon sequestration through shell calcification, but also significantly impact the marine carbon cycle through their physiological activities and post-mortem degradation processes. This study aims to accurately quantify the carbon content of shells and understand the degradation rates of shell carbon, providing fundamental data for deeper investigation into the role of shellfish in marine carbon sequestration.According to the findings of this study, R. philippinarum and C. gigas, as widely distributed representative species in coastal aquaculture systems, exhibit significant carbon sequestration potential. Therefore, further research and optimization of the cultivation models for these bivalves hold considerable theoretical and practical significance for enhancing marine carbon sequestration capacity and mitigating global climate change.