钩虾对大型海藻的摄食选择及其潜在的碳汇分析

The feeding selectivty of amphipod Eogammarus possjeticus on macroalgae and its potential carbon sink analysis

关键词:  端足类  中华原钩虾  大型海藻  摄食率  碳汇

Key words:  Amphipod  Eogammarus possjeticus  Macroalgae  Feeding rate  Carbon sink

摘要:

经食物链形成的“碳封存”和“碳转移”是海洋渔业碳汇的重要方面。大型海藻是海洋生态系统中最主要的初级生产力之一，也是最高效的固碳生物类群之一，端足类是大型海藻群落中非常重要的消费类群，处于食物链物质循环和能量传递的中间环节，承担着“碳转移”的职责。本文以山东半岛端足类中华原钩虾(Eogammarus possjeticus)为实验对象，开展了其对5种大型海藻[浒苔(Ulva prolifera)、肠浒苔(U. intestinalis)、扁浒苔(U. compressa)、线形硬毛藻(Chaetomorpha linum)和丝毛藻(Cloniophora sp.)]的摄食研究，比较了中华原钩虾对5种大型海藻的摄食率，分析了摄食率与海藻的总有机碳(TOC)、总氮(TN)、碳氮比(C/N)和干湿比(DW/FW)等指标的相关性，揭示了中华原钩虾对海藻的摄食选择性特征，初步探讨了钩虾潜在的碳汇影响。结果显示，中华原钩虾对肠浒苔和浒苔具有较高的摄食率，分别为0.81和0.80 g鲜重/(g·d)，而对线性硬毛藻摄食率最低，为 0.19 g鲜重/(g·d)；中华原钩虾选择栖息于大型海藻的个体数量比例以丝毛藻最高，其次为肠浒苔和浒苔；中华原钩虾的摄食率与海藻TOC含量和C/N呈显著正相关(P<0.05)，而与TN含量和DW/FW呈显著负相关(P<0.05)。研究表明，中华原钩虾对大型海藻的摄食选择与海藻TOC、TN、C/N和DW/FW均显著相关，且偏向于在结构复杂、细丝状分枝多而密集的海藻中栖息。钩虾优先选择固碳量较高的浒苔类绿藻，能够快速将其固定的碳向更高营养级传递转移，可加速实现碳封存或碳移出，对海洋渔业碳汇进程可能会产生影响。

Abstract:

Carbon sequestration and carbon transfer through the food chain are important aspects of the carbon cycle in marine fisheries, and an essential part of the blue carbon sink of marine organisms. It includes not only the carbon used in shellfish and macroalgae farming at lower trophic levels in the food web, but also by certain organisms through feeding and growth activities. In marine ecosystems, macroalgae are one of the most important primary productive forces and one of the most efficient carbon-fixing organisms. They directly absorb carbon dioxide from seawater through photosynthesis, increasing the ocean carbon sink. Moreover, they promote and accelerate the diffusion of atmospheric carbon dioxide into seawater, helping to reduce it in the atmosphere. Macroalgae support many marine biota, including amphipods. Amphipods not only use the macroalgae habitat as shelter and nursery, but also as a source of nutrition. Moreover, amphipods provide a critical food source for other marine animals, such as fish, crustaceans, cephalopods, and even gray whales. Therefore, amphipods play an essential role in the material circulation and energy transfer in the food chain of the marine ecosystem. As primary consumers, the amphipods may also play an important role in the carbon sink process of marine fisheries by transferring the macroalgae fixed carbon to senior consumers. Additionally, amphipods prioritize ‘delicious’ macroalgae rather than treat them equally like many other invertebrates. They also reduce the biomass accumulation of this macroalgae and even affect its community structure. Consequently, studying the amphipods feeding selectivity to macroalgae is essential to understanding the relationship between macroalgae and algae-dwelling animals. Based on the above research background, this study investigated the feeding selectivity characteristics of Eogammarus possjeticus, an amphipod from the Shandong Peninsula, in relation to five different macroalgae, including Ulva prolifera, U. intestinalis, U. compressa, Chaetomorpha linum, and Cloniophora sp. The potential amphipods’ carbon sink characteristic was preliminarily discussed. The results showed that the feeding rates of E. possjeticus on U. intestinalis and U. prolifera were the highest, with daily feeding rates of 0.81 g of fresh weight/(g·d) and 0.80 g of fresh weight/(g·d), respectively, while the feeding rate of E. possjeticus on C. linum was the lowest of 0.19 g of fresh weight/(g·d). The proportion of E. possjeticus individuals living in macroalgae was the highest in Cloniophora sp., followed by U. intestinalis and U. prolifera. We analyzed the correlation between total organic carbon (TOC), total nitrogen (TN), carbon/nitrogen ratio (C/N), and dry weight/fresh weight ratio (DW/FW) of the macroalgae, as well as with the E. possjeticus feeding rate. A significant positive correlation was observed between the feeding rate and the macroalgae TOC concentration and C/N ratio (P<0.05). Nonetheless, the feeding rate negatively correlated with the TN concentrations and DW/FW ratio (P<0.05). These results suggested that the feeding selectivity of E. possjeticus to macroalgae was significantly correlated with TOC, TN, C/N, and DW/FW. It seemed that amphipods prefer to inhabit filamentous algae with complex structures and dense branches. In fact, amphipods give priority to Enteromorpha genus species with rapid growth rate and high carbon sequestration, which can accelerate the carbon transfer process of macroalgae to a higher trophic level species. The carbon transfer process enables marine animals at the top of the food chain to store carbon in the form of biological pumps. With the harvest of fisheries, some marine animals are removed from the seawater to promote carbon removal, while other animals not captured by humans continue to conduct carbon uptake and food chain transmission. In conclusion, amphipods have feeding selectivity to macroalgae, which may play the important role of carbon transfer channel in accelerating carbon sinks in marine fisheries.