| 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. |
