| With the rapid development of the marine economy,the marine environment is facing unprecedented pressure,with approximately 8 million pieces of marine debris being produced globally every day,and the amount of marine debris is also continuously increasing.Mangrove is an important coastal wetland ecological type in the coastal intertidal zone,and is a highly concentrated area of biological activities that have special value for maintaining biodiversity and resource productivity.Macrobenthos are an indispensable part of the mangrove ecosystem.With the increasing pollution of the marine environment,the mangrove ecosystem has been severely damaged.There has been an increasing number of studies on the impact of mangrove habitat changes on the community and feeding of macrobenthos.However,such studies have mostly focused on the impact of coastal engineering,pond reclamation,aquaculture and sewage disposal on the mangrove macrobenthos,while less attention has been paid to the issue of marine floating garbage accumulation in mangroves.The coastal areas of Fujian Province are seriously polluted by marine floating debris.The Jiulong River Estuary Mangrove Nature Reserve is located at the estuary of the lower reaches of the Jiulong River and is very close to the living quarters of local residents,making it easy for the mangroves in this area to intercept all kinds of marine debris from the Jiulong River and coastal areas.In this study,the mangrove sites affected by marine debris deposition and the reference sites slightly affected were selected in two locations,i.e.,Fugong and Haimen Island in Jiulong River Estuary,respectively.Seasonal samplings of macrobenthos communities were conducted in August,November 2019 and January and April 2020 in these sites.Species composition,community structure and biodiversity index were compared among the mangroves sites,and the stable isotopic and fatty acid composition were also compared,to explore the impact of marine debris on the community structure and food sources of macrobenthos in mangrove.In this study,a total of 30 species of macrobenthos were collected and identified,including 11 species of molluscs,13 species of arthropods,3 species of annelids,1species of sipunculates,1 species of vertebrates and 1 species of neophytes.Molluscs ccounted for 36.67%of the total species,and arthropods accounted for 43.33%of the total species.The major species collected in this study include Corbicula nitens,Assiminea brevicula,Uca arcuata,Metaplax longipes,Sesarma plicata,Alpheus hoplocheles,Phascolosoma esculenta and Notomastus aberans.The deposition of marine debris in mangroves had a significant impact on the density of macrobenthos in mangroves,but not on biomass.Arthropods and sipunculates in different groups of macrobenthos are more affected.The statistical results of biodiversity showed that the species diversity index（d）,Shannon-Weiner index（H’）and Pielou’s species evenness index（J’）of macrobenthos in different types of mangrove sites were in the order of debris-deposited-sites>reference sites,but the density of dominant species in mangrove show ed a downward trend in debris-deposited-sites.There were differences in stable isotopic signatures among different food sources.The lowestδ13C value was Kandelia obovata leaves（32.01±1.29‰）,the highest was Spartina alterniflora leaves（15.33±0.53‰）,the lowestδ15N value was K.obovata leaves（1.41±0.39‰）,and the highest was found in SPOM（7.05±1.72‰）.In different sites,theδ13C of K.obovata leaves in the reference sites was lower than that in the deposited sites,and theδ13C value of surface sediment in reference site was higher than that of the deposited site.The impact of marine debris om macrobenthos varied with benthos species,and theδ15N value of arthropods was less variable than those of other benthos species.The stable isotope values of Uca arcuata was closer to S.alterniflorus and the change in stable isotopic values with sampling sites were minor.The stable isotopic values of sesarmid crabs were more close to SPOM,and the respectiveδ13C andδ15N values were generally more enriched in deposited sites than reference sites.The feeding of macrobenthos is mainly related to their living place.Marine debris deposition changed the habitat environment of macrobenthos,thus changing the food source compositions of macrobenthos.According to the food sources analysis of marobenthos,K.obovata leaves accounted for<20%to the food sources of macrobenthos,while S.alterniflora and SPOM were the main food sources of most species.In this study,we determined the fatty acid composition of K.obovata leaves,S.alterniflora leaves,sediments,and the samples of U.arcuata and S.plicata.A total of19 fatty acids were detected in K.obovata leaves,with higher proportions of C16:0,C18:0 and C18:2n6c.A total of 17 fatty acids were detected in S.alterniflora leaves,with higher proportions of C16:0,C18:2n6c and C18:3n3.The C22:ln9 in sediment had a different proportion from that in plant leaves.A total of 14 fatty acids were detected in Uca arcuata,of which C23:0,C16:0,C18:ln9c and C22:ln9 were higher in proportion.Among the fatty acids with high proportions,the long-chain saturated fatty acids showed higher proportions in debris-deposited sites than in reference sites,and short chain saturated fatty acids and unsaturated fatty acids showed less proportions in debris-deposited sites.A total of 13 fatty acids were detected in S.plicata,among which C16:0,C18:0,C18:2n6c and C22:ln9 were more abundance,and the proportions of saturated fatty acids was generally higher in debris-deposited sites.The results of fatty acid markers showed that the S.plicata crabs were more likely to feed on S.alterniflora and K.obovata,while the fiddler crabs,U.arcuata,were more likely to feed on sediments.Mangrove debris deposition resulted in the incorporation of S.alterniflora detritus in the sediment by fiddler crabs.The fiddler crabs in the debris-deposited sites had a more uptake of terrestrial sources than the reference sites,Mangrove debris accumulation also affects the feeding of S.plicata,and the S.plicata in the debris-deposited sites would graze more mangrove leaves.The fatty acids,such as C23:0,C18:0 and C16:0,contributed substantially to change in fatty acid composition of U.arcuata related to the debris deposition,and C16:1,C18:2n6c and C16:0 mainly account for the change in fatty acid composition of S.plicata crabs. |
