| With population dramatic explosion and city large urbanization,the Shanghai development has been limited by the scarcity of land resources.In order to efficiently solve agrarian problems,the intertidal wetlands in Yangtze estuary have been widely reclaimed recently.As a result,the natural habitats are destructed in this place but the effect has not been researched.Macrobenthos are major animals in estuarine ecosystem,and are ideal indicators of environmental changing because of their low mobility and high sensitivity.In order to study the impact of reclamation project on intertidal macrobenthos in estuarine ecosystem,long-term investigations were carried out in east shoal of Hengsha island and Chongming island.The relation between main environmental indicators and macrobenthic communities was analyzed.Moreover,macrobenthic diversity in artificial oyster reef of Yangtze Estuary was investigated to preliminarily explore appropriate method for the restoration of macrobenthic communities.On this basis,the desalination process of reclamation wetland was simulated to discuss the changes of physiological measures,including osmoregulation,metabolism,immunization and digestion and reproductive measures,including gonadal development,mating behavior,and embryo development of the dominant species Chiromantes dehaani.This study was expected to understand influence mechanism of reclamation on macrobenthos in Yangtze estuary.The results are listed as follows:1 Influence of reclamation on macrobenthic communities in east shoal of Hengsha island and Chongming island1.1 Community structure of macrobenthos in east shoal of Hengsha islandIn this study,macrobenthic community in east shoal of Hengsha island was investigated in April,July,October and December from 2012 to 2015.Five different regions were set:reclamation region inside dike(RI)and control region(RIC),reclamation region outside dike(RO)and control region(ROC),restored region(R).The results showed that a total of 38 species were recorded in east shoal of Hengsha island.The regions R and RIC were relatively high in the number of species and dominant species,abundance,biomass,and diversity indices,while those were at low levels in region RI.An obvious change in original community had occurred in RI during the past four years,and Chironomid larvae had replaced the advantage of original dominant species,such as Assiminea sp.and Illyoplax deschampsi after one year of reclamation.The degree of community degradation was lower in RO than in RI.However,the community in RO was at low level because of narrow and bald tidal flat.There was an obvious restoration of macrobenthic community in region R during this period,especially for small individuals.The cluster and MDS analysis indicated that there were obvious differences in community structures among five regions.Chironomid larvae and Assiminea sp.were confirmed as main species in describing communities differences by SIMPER analysis.The above evidence suggested that the community structure of macrobenthos have been affected by reclamation project in east shoal of Hengsha island.Moreover,there is a possibility of self-restoration of macrobenthic community in tidal flats disturbed by reclamation.1.2 The characteristics of macrobenthic communities and its relation with environmental indicators in east shoal of Hengsha islandIn this study,macrobenthic communities were investigated in five sampling regions of east shoal of Hengsha island from April 2012 to December 2012.The results showed that there was a significant spatial difference in abundance and biomass of macrobenthos(P<0.05).Significant correlations between macrobenthic communities and environmental indicators were verified in region RI,RO,and R.BIO-ENV analysis indicated that salinity and water content in region RI,the dissolved oxygen,pH,and Sand content in RO,and water temperature and stem abundance in R were the main environmental indicators that affecting community structure of macrobenthos.The benthic health was described with the funnel plots and Abundance-Biomass Curve method.A moderate human disturbance was observed in benthic habitat of region RI,while the regions RO and R were perturbed by moderate natural factors.Therefore,the reclamation may have a negative influence on benthic health and macrobenthic communities.The degradation of macrobenthic communities may caused mainly by salinity and water content.1.3 Community structure of macrobenthos in east shoal of Chongming islandIn this study,several investigations on macrobenthos in east shoal of Chongming island were conducted in April;July,October and December from 2014 to 2015.Four regions were set:reclamation region inside dike(RI)and control region(RIC)and reclamation region outside dike(RO)and control region(ROC).The results showed that a total of 35 species were collected from east shoal of Chongming island.The number of species,biomass and species diversity measures were relatively high in region RO,and the region RIC were at high levels in abundance and ?+ value.In contrast,the abundance,biomass,species richness,and ?+ index got low values in region RI,and the region ROC were at low levels in species evenness and ?+ value.A deleterious change in diversity indices had occurred in RI from 2014 to 2015.Meanwhile,Chironomid larvae took a dominant position in macrobenthic community,However,no obvious variations were observed in the other regions during this period.The cluster and MDS analysis indicated that community structure of region RI in 2015 was obviously different with the other regions.Assiminea sp.,Stenothyra glabra,and Chironomid larvae were confirmed as main species in describing communities differences by SIMPER analysis.In summary,the reclamation project had a deep influence on community structures in east shoal of Chongming island,which caused a degradation in community diversity inside the reclamation dike.However,the community status outside dike was superior to other regions.1.4 The characteristics of macrobenthic communities and its relation with environmental indicators in east shoal of Chongming islandIn this study,the relation between macrobenthic community and environmental indicators in east shoal of Chongming island from April to December in 2014.The results showed that there was a significant seasonal difference in biomass of macrobenthos(P<0.05),but no significant variations were observed among seasons and regions(P>0.05).Macrobenthic community in RI was highly related to environmental indicators through correlative analysis.BIO-ENV analysis indicated that salinity,water content,and stem abundance in region RI were the main environmental indicators that affecting community structure of macrobenthos.The benthic health in RI,RIC,and RO had suffered from different levels of outside interference,and significant human disturbances were observed in regions RI and RIC with funnel plot method.The above results indicated that the benthic habitat had been seriously interfered with reclamation project.The variations of salinity,water content,and stem abundance in reclamation wetland were considered as the main environmental indicators which causing the degradation of macrobenthic communities.1.5 The ecological research on macrobenthic diversity in artificial oyster reef of Yangtze EstuaryIn this study,several investigations on macrobenthic diversity were conducted in the largest artificial oyster reef,Yangtze Estuary Oyster Reef,in China from 2013 to 2014.The diversity data were considerably higher in the sampling sites of south branch than in corresponding locations of north branch.The richness measures showed a significant increasing trend from low-salinity zone to high-salinity zone,while evenness measures were typically high in middle-salinity zone.Our investigated results were combined with historical data to detect the decade change in macrobenthos.The variation in substrate organisms and macrobenthic diversity followed a similar trend of a gradual steady after a large fluctuation.Redundancy analysis indicated that water salinity and substrate factors were main indicators that influence the distribution of macrobenthic distribution.The departures of taxonomic measures(?+ and ?+)from expected limits were used to test ecological health status.All sampling sites in south branch were protected by Nature Reserve.However,the N2 and N6 in north branch were respectively subjected to severe and mild human interventions.2 Influence of salinity decrease on physiological measures of Chiromantes dehaani2.1 Influence of salinity decrease on osmotic pressure,ionic concentration,and Na+/K+-ATPase activities of Chiromantes dehaaniIn this study,different salinity levels(24‰,18‰,12‰,6‰,0‰0d,0‰24d)were set to simulate the process of salinity decrease in reclamation wetland.The changes in haemolymph osmolality,ionic concentrations,and Na+/K+-ATPase activity of male and female Chiromantes dehaani were investigated.Results showed that isosmotic points of female and male crab were 609 mOsm/kg H2O and 599 mOsm/kg H2O,respectively.The isosmotic salinity was close to 20‰.With salinity decrease,a significant decrease was observed in haemolymph osmolality,Na+,Cl-,and K+concentrations,while Ca2+ concentration and Na+/K+-ATPase activity had an increase trend.After 0‰,the concentration of Na+ and Cl-exhibited an obvious increase,but a decrease trend was observed in osmolality,concentration of K+ and Ca2+,and Na+/K+-ATPase activity.No significant variation appeared in haemolymph osmolality,ionic concentrations,and Na+/K+-ATPase activity between male and female Chiromantes dehaani.2.2 Influence of salinity decrease on metabolic response of Chiromantes dehaaniIn order to understand metabolic response in the osmoregulation process of Chiromantes dehaani,the variations of protein,lipid,and carbohydrate were determined after gradual reduction of water salinity.Results showed that protein content in hemolymph and hepatopancreas and lipid content in gills of female and male crabs,triglycerides content in hemolymph of females,and glycogen content in hepatopancreas of males maintained relatively stable in the range of 24-12‰,while a significant raise occurred after 12‰(P<0.05).There was a slight increase in cholesterol and glucose content in both sexes between 24‰ and 18‰,and a decrease below 18‰.After 0‰,a significant decrease was observed in protein content in hemolymph and hepatopancreas and total lipid in gills(P<0.05).The metabolic indices were slightly higher in males than in females.2.3 Influence of salinity decrease on digestive enzymes activities of Chiromantes dehaaniIn this study,the digestive ability of Chiromantes dehaani were evaluated with the activities of several enzymes,including amylase,cellulose,pepsin,trypsin,and lipase.Results showed that pepsin activities increased significantly in stomach and hepatopancreas of males and in stomach of females during 6-0‰,while a significant raise of trypsin activities were tested in the same tissues after medium salinity dropped to 12‰.By contrast,the activities of cellulose in hepatopancreas and amylase in stomach were inhibited after 18.Meanwhile,the same trend occurred in amylase activities of male hepatopancreas and the value of A/T.There was no significant change in activities of digestive enzymes from 0‰0d to 0‰24d,except for amylase activities in male stomach.All digestive enzymes got higher activities in females than in males,except lipase.2.4 Influence of salinity decrease on immune factors of Chiromantes dehaaniIn this study,several immune factors,including total haemocyte count and activities of phenoloxidase,lysozyme,alkaline phosphatase,and superoxide dismutase,were tested to observe the variation of immunity of Chiromantes dehaani with salinity decrease.Results showed that activities of phenoloxidase and alkaline phosphatase in hepatopancreas and phenoloxidase in hemolymph remained relatively steady when medium salinity was higher than 12-6‰,thereafter,these enzymes were significantly activated(P<0.05).Meanwhile,the same trends were observed in the activities of superoxide dismutase in hepatopancreas and hemolymph of male crabs.In contrast,there was a slight raise in total haemocyte count and activities of hepatopancreas lysozyme during 24-18‰,and a general decline after 18‰.All the activities of immune enzymes were inhibited after medium salinity dropped to 0‰,except lysozyme in hemolymph.Immune parameters except for SOD of females were considerably higher than those of males.The present results indicated that Chiromantes dehaani had an ability of osmoregulation,and the salinity of isosmotic medium approached to 20‰.Most metabolic measures got a low content in 24-18‰ and a high content in 6-0‰.The immune enzymes were significantly activated in salinity range of 12-0‰ except for lysozyme.Meanwhile,there was a significant enhancement in the ability of protein digestion in 12-0‰,while carbohydrate digestion was generally inhibited under this salinity.The females got high activities in immune and digestive enzymes,indicating a strong adaptive capacity to salinity change.However,the metabolism and immunity parameters of Chiromantes dehaani were generally inhibited under long-term freshwater stress.The variations of physiological measures may cause negative influences on survival and development of the population,which ultimately resulted in the degradation of Chiromantes dehaani in reclamation wetland3.Influence of salinity decrease on reproduction measures of Chiromantes dehaani3.1 Gonadal development,mating,and spawning of Chiramantes dehaaniIn this study,the process of salinity decrease in reclamation wetland was simulated with an acute stress method.The gonadal development and mating behavior of Chiromantes dehaani were investigated under the salinity of 24‰,18‰,12‰,6‰,and 0‰.Lipid contents in ovaries and hepatopancreas were also tested at different salinities.Results showed that:(1)the gonadal indices got higher values in group 12-24‰ of females and group 6-18v of males than in group 0‰ of both sexes from 12d to 48d;(2)the hepatosomatic indices in group 12-24‰ were higher than in group 0‰ during 24-48d for males and females;(3)the lipid contents of ovaries in group 12-24‰ were significantly higher than that in group 0‰ from 12d to 48d,while lipid contents of hepatopancreas got a lower value in group 18-24‰v than in group 0‰;(4)at day 24,few mating behaviors had occurred in group 12-18‰ and no female crabs spawned during this period;(5)at day 48,over 75%fermales were fertilized in group 6-24‰,while 12.5%of females in 12-24‰ spawned during six days of post-mating.The above results indicated that gonadal development of males and females may experience some restrictions in freshwater,which can further influence the mating and spawning bahaviors.3.2 Survival and development of embryo of Chiromantes dehaaniIn order to understand the influence of salinity decrease on survival and development of embryo of Chiromantes dehaani,the spawning crabs were exposed to different salinities.Results showed that there was an obvious raise in the quantity of aborted embryos under medium salinity of 0‰.The cleavage and gastrula stages got an aborted rate of 100%at 144h and 240h in freshwater environment.Moreover,a low success rate of embryo development was observed in salinity of 0‰,and only 14%of heartbeat stage embryo can develop to pre-hatching stage.In contrast,the lowest abortions were observed in cleavage,gastrula,and eyespot stages of 12‰(12-19%of group 0‰)and in heartbeat stage of 6‰(22%of group 0‰),while the fastest development to pre-hatching stage occurred in eyespot(240h)and heartbeat(144h)stage of 12‰ and all stages of 6‰(144-288h).The present research proved that the optimum salinity for embryo development was 6-12‰.However,the abortion rate got a far higher value in group 0‰ than in other groups.This result may impede the process of larvae supplement of Chiromantes dehaani.In conclusion,the freshwater habitat may restrain gonadal development,mating,and spawning of Chiromantes dehaani.Meanwhile,the abortion rate had a significant increase in freshwater environment,which further act as a barrier in population growth.Therefore,the breeding failure caused by salinity decrease may be the main reason for population degradation of Chiromantes dehaani in reclamation wetland. |
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