Nutritional Sources Analysis And The Heavy-metal Enrichment Of The Macrofauna From The Deep-sea Chemotrophic Ecosystem

The deep-sea chemotrophic ecosystem has always been the forefront and hotspot in the research because of the special characteristics of physical and chemical environment and communities.The deep-sea hydrothermal and cold seep ecosystems are most important parts.Since hydrothermal and cold seep ecosystems discovered,people have been exploring.Studying nutritional sources and the heavy-metal enrichment of macrofauna in the special environment could help to explain the survival strategies and adaptability and understand the process of material circulation and energy flow.The stable isotope approach and the fatty acid biomarkers detection were used as principal methods,and the stomach content analysis was used as the complement.We used samples collected in May-July 2015 and June-September 2016 by the R.V.Kexue to measure and analyze the values and compositions of the stable isotope and fatty acid in the macrofauna from the Formosa Ridge cold seep in the South China Sea,the Manus basin hydrothermal vents and the Okinawa Trough hydrothermal fields.We analyzed nutritional sources and feeding habits of the macrofauna.Four major animals from the cold seep in the South China Sea were chosen to analyze food source ratios using a mixing model for the first time.We quantitied the contribution of each source for food.B.platifrons reilid on endosymbiotic bacteria mostly,which accounted for 95%.While particulate organic matter took up 5%.Two crustaceans were omnivorous and relied on predation.While particulate organic matter took up 30%.Lithodes longispina preyed on animals in the cold seep ecosystem mostly.We took the results from other areas and behavior characteristics of animals into account and then described the food web model for the first time.B.platifrons,Bathyacmae lactea and Provanna glabra were at the second level,which were primary consumers.Branchipolynoe pettibonae,Alvinocaris longirostris,Shinkaia crosnieri and Phymorhynchus buccinoides were at the third level,which were secondary consumers.The invader L.longispina was at the highest level,which was the top predator.The characteristics of the stable isotope and fatty acid in mussels from different sites were compared to analyze the effect of different sites on nutritional sources.We used B.platifrons from the Formosa Ridge cold seep in the South China Sea as the research object to measure the component of heavy metals and explain these distribution patterns from the perspective of adaptability and biological function.We analyzed the data of B.platifrons,B.lactea,S.crosnieri,A.longirostris,B.pettibonae,Phymorhynchus buccinoides,P.glabra and the invader L.longispina from the ecosystem of the Formosa Ridge cold seep in the South China Sea.Theδ¹³C values of all specimens were below-40‰,and the compositions of fatty acids were dominated by monounsaturated fatty acids.Methane-based bacteria is the major primary producer in this ecosystem.B.platifrons was the major primary consumer relied on endosymbiotic bacteria.B.lactea was a secondary consumer relying on microorganism and organic detritus in this ecosystem.Among food sources,microorganism was the main source.The gastropod P.glabra was a secondary consumer relying on microorganism and organic detritus.However,compared with B.lactea,the food source was more from organic detritus.The other gastropod P.buccinoides was a secondary consumer relying on cadavers and the upper organic detritus.Compared with the little gastropod P.glabra,the food sources were more from photosynthesis ecosystem.B.pettibonae was a secondary consumer relying on mussels and carcass from highly trophic animals.A.longirostris was a secondary consumer as an omnivorous animal,relying on particle organic matter and low trophic level organisms.S.crosnieri was a secondary consumer as an omnivorous animal,relying on epibiotic microorganisms,particle organic matter and low trophic level organisms.The invader L.longispina was the top predator,relying on animals from the cold seep majorly and little particle organic matter.In the Manus basin hydrothermal vents ecosystems,we analyzed the data of Munidopsis lauensis,Chorocaris vandoverae,Bathymodiolus manusensis,Arcovestia ivanovi,Ifremeria nautislei and Provanna nassariaeformis.Theδ¹³C values of all specimens were above-35‰,and the compositions of fatty acids were dominated by monounsaturated fatty acids except of P.nassariaeformis.Sulfur-based bacteria is the major primary producer in this ecosystem.B.manusensis was the major primary consumer relied on endosymbiotic bacteria.The endosymbionts used the CBB cycle and with Rubisco formⅠas the CO2-fixing enzyme.Commensal polychaetes mostly obtained their nutrition from their hosts.Vestimentiferans obtained food from symbiotic bacteria,which belonged to different types from the bacteria in mussels.I.nautislei and P.nassariaeformis both relied on organic detritus and cadavers in the hydrothermal ecosystem.The latter one relied on more sources from photosynthesis ecosystem.M.lauensis and C.vandoverae as omnivorous animal relied on particle organic matter and low trophic level organisms.In the ecosystems of the Okinawa Trough hydrothermal fields,we analyzed the data of A.longirostris,Shinkaicaris leurokolos,B.pettibonae and Paralvinella hessleri.Theδ¹³C values of all specimens were above-35‰,and the compositions of fatty acids were dominated by monounsaturated fatty acids except of B.pettibonae from Dive#102.Methane-based and sulfur-based bacteria are both major primary producer in this ecosystem.B.platifrons was the major primary consumer relied on endosymbiotic bacteria.Moreover,it had sources from the filtration,especially in the Dive#102 field.B.pettibonae survived in the cavity of mantles,relying on its host mostly,microorganisms,cadavers and organic detritus were all nutritional sources.P.hessleri obtained food from symbiotic bacteria,which belonged to different types from the bacteria in mussels.The symbionts were sulfur-based bacteria primarily.A.longirostris and S.leurokolos were both relied on chemoautotrophic bacteria and low trophic level organisms.However,the bacteria they used were different.The former one used the bacteria which fixed carbon with the CBB cycle,while the latter one used the bacteria which fixed carbon with the rTCA cycle.We compared the data of mussels from deep-sea chemotrophic ecosystems and Modiolus kurilensis from coastal waters.M.kurilensis was significantly different from mussels from deep-sea chemotrophic ecosystems in several aspects.Theδ¹³C values of M.kurilensis were above-20‰,and the compositions of fatty acids were dominated by polyunsaturated fatty acids.The components of fatty acid were rich in the types of C20:5ω3 and C22:6ω3.We can inferred that they obtained food by filter-feeding,and the food sources were from photosynthesis ecosystem,mainly from algae.However,mussels from deep-sea chemotrophic ecosystems relied on chemoautotrophic bacteria mainly.We quantified the presence of twenty elements in gills,mantles and shells of Bathymodiolus platifrons from the Fomosa Ridge cold seep in the South China Sea.We found that most elements were significantly enriched in the gills,which could be related to food uptake and the existence of endosymbionts.In shells and mantles,Mn was particularly rich,possibly due to its replacement of Ca in the carbonate structure.A significant positive correlation among Ca,Sr,and Mg was found in both gills and mantles,consistent with relationships observed in vent and littoral mussel species.Compared with other deep-sea environments and coastal areas,metal accumulation showed local variability but similar overall patterns of uptake and accumulation,indicating that essential elemental requirements in different mussel species may be similar across taxa.The high bioconcentration factor（BCF）values of Mn and Ag suggest that their particular functions and regulation mechanisms are related to specific adaptations and life cycle processes.