Ecological Niche Difference Of Boleophthalmus Pectinirostris And Periophthalmus Magnuspinnatus Located On The Wetland Of The Yangtze Estuary

The Yangtze River estuary wetland is an important distribution area of estuary salt marsh.The Yangtze River estuary wetland has high biodiversity,including diverse primary producers,benthic organisms,insects and so on.It can provide abundant food resources for many swimming animals and birds,supporting the estuary and coastal aquatic food network.The mudskippers,widely distributed in the wetlands of the Yangtze River estuary,play an important role in maintaining healthy tidal wetland ecosystems as tidal flat resider.They participate in the food web material circulation and energy flow in tidal wetlands.This paper explores the spatial distribution characteristics,dietary characteristics,food source characteristics and intestinal flora structure of Boleophthalmus pectinirostris and Periophthalmus magnuspinnatus widely distributed in the wetlands of the Yangtze River estuary.And this paper attempts to elucidate the ecological niche differences of B.pectinirostris and P.magnuspinnatus from the perspective of distribution,diet,food source and microorganism.The main results are as follows:1.The distribution characteristics of B.pectinirostris and P.magnuspinnatus are studied in the northern Spartina alterniflora habitats and southern tidal channel habitats of Chongming Dongtan of the Yangtze River estuary.It is found that the number of B.pectinirostris is less in the sampling sites near the shore and is more in the sampling sites farther away from the shore in the northern Spartina alterniflora habitats of Chongming Dongtan?p<0.05?.While,the number of P.magnuspinnatus is relatively large in the sampling sites near the shore and is minimal in the sampling site farthest away from the shore.In the southern tidal channel habitat,B.pectinirostris is mainly distributed in the middle and lower part of the tidal channels,and there is no distribution in the upper part of the tidal channels.However,P.magnuspinnatus is mainly distributed in the upper and middle parts of the tidal channels,and the lower part is also distributed but relatively few.These findings indicate that there is a certain spatial distribution ecological niche difference between B.pectinirostris and P.magnuspinnatus in the same habitat.Correlation analysis with environmental factors find that the relationships between the mudskippers?B.pectinirostris and P.magnuspinnatus?and environmental factors are different in different habitats.In the northern S.alterniflora habitats,the correlation coefficients between the mudskippers?B.pectinirostris and P.magnuspinnatus?and the soil moisture content are the largest.In the southern tidal channel habitats,the correlation coefficient between B.pectinirostris and soil moisture content is the largest,but for P.magnuspinnatus,the correlation coefficient of the soil clay content is the largest.In addition,the distribution of B.pectinirostris is positively correlated with the soil moisture content,and P.magnuspinnatus is negatively correlated with the soil moisture content,indicating that B.pectinirostris is more aquatic than P.magnuspinnatus.2.The feeding characteristics of mudskippers?B.pectinirostris and P.magnuspinnatus?located on different habitats?northern S.alterniflora habitats,middle Phragmites australis habitats,and southern tidal channel habitats?are studied using traditional but intuitive gastrointestinal content anatomy experiments.The results show that the empty stomach rate of B.pectinirostris in different habitats is 3.3%,0.0% and 8.6%,respectively.But for P.magnuspinnatus,the value is 100%,93.9% and 87.5%,respectively.It makes clear that the feeding intensity of B.pectinirostris is significantly greater than P.magnuspinnatus.In frequency analysis of the food composition of B.pectinirostris,algae and detritus both account for 95.4%,and shrimp and others?animal eggs?account for 3.9% and 0.6%,respectively,indicating the B.pectinirostris is herbivorous and partially omnivorous fish.While for P.magnuspinnatus,algae,detritus,insects,shrimp,crabs and others?animal eggs?are found with a frequency rate of 14.3%,28.6%,28.6%,42.9%,42.9% and 28.6%,indicating the diets of P.magnuspinnatus is omnivorous and P.magnuspinnatus is omnivorous and partially carnivorous fish.There is a significant difference in food ecological niche between B.pectinirostris and P.magnuspinnatus.The qualitative and quantitative analysis of the algae that was ingested by the B.pectinirostris show that B.pectinirostris mainly eat diatoms and the dominant algae species?>10%?is different in different habitats.In the northern S.alterniflora habitats,Skeletonema sp.?belonging to the diatom?is the dominant algae,and account for 73.28±25.91%.In middle P.australis habitats,Navicula sp.?belonging to the diatom?and Pleurosigma affine?belonging to the diatom?are the dominant algae,and account for 65.07±25.10 % and 27.28±20.04 %,respectively.In the southern tidal channel habitats,Pleurosigma affine?belonging to the diatom?,Navicula sp.?belonging to the diatom?and Trichodesmium thiebautii?belonging to the Cyanophyta?are the dominant algae,and account for 40.51±18.22 %,20.88±11.43%,and 10.69±23.64%,respectively.The diversity analysis show that the algal species richness,Evenness,Shannon index and Simpson index of the southern tidal channel habitats are all greater than these of the northern S.alterniflora habitats and the middle P.australis habitats,suggesting that the algae microecosystem in the southern region of Chongming Dongtan with more native plants was more stable,and the food study of the B.pectinirostris had certain environmental indicators.3.The differences of food sources of B.pectinirostris and P.magnuspinnatus in different areas with different degrees of S.alterniflora invasion are studied using isotopic technique to explore the food source ecological niche of B.pectinirostris and P.magnuspinnatus and explore whether the exotic plant S.alterniflora have been incorporated into aquatic food webs of the Yangtze River estuary by the mudskippers?B.pectinirostris and P.magnuspinnatus?.The results show that ?¹⁵N value of P.magnuspinnatus is significantly greater than that of B.pectinirostris,indicating that the trophic level of P.magnuspinnatus is greater than that of B.pectinirostris.In the same sampling area,the ?¹³C value of B.pectinirostris is significantly greater than that of P.magnuspinnatus,indicating that the low trophic level B.pectinirostris has a more enriched ?¹³C value than the high trophic level P.magnuspinnatus.This implies that there is a significant feeding segregation between B.pectinirostris and P.magnuspinnatus.Food source contribution analysis shows that the contributions of S.alterniflora to B.pectinirostris in different sampling sites?southern,middle,and northern part?is 42%?18%-60%?,80%?74%-86%?,and 96%?96%-96%?,respectively.To P.magnuspinnatus,the corresponding value is 16%?0-40%?,28%?0-48%?and 82%?76%-88%?to.These findings indicate that the invasive plant S.alterniflora have been incorporated into the wetland ecosystem by the mudskippers?B.pectinirostris and P.magnuspinnatus?.In the area of serious invasion,S.alterniflora presents a larger contribution and has a greater impact on the ecosystem.The low trophic level B.pectinirostris is more sensitive to invasive S.alterniflora than the high trophic level P.magnuspinnatus,and more suitable to be an indicator organism.4.The gut microbiota of the male and the female of B.pectinirostris and P.magnuspinnatus are sequenced using high-throughput sequencing techniques to explore the differences in ecological niche from the microbial perspective.The results show that Proteobacteria is the dominant bacteria in all sample groups.In the male and female sample groups of B.pectinirostris,Proteobacteria account for 73.5% and 52.6%,respectively.In the male and female sample groups of P.magnuspinnatus,Proteobacteria account for 40.2% and 40.9%.Besides Proteobacteria,Fusobacteria?18.2%?and Spirochaetes?10.5?are the dominant bacteria?the relative abundance >6%?in the female samples of B.pectinirostris.Firmicutes?20%?,Actinobacteria?7.5%?,Bacteroidetes?7.4%?,and Acidobacteria?7.2%?are the dominant bacteria in the male samples of P.magnuspinnatus.Cyanobacteria?22.2%?,Spirochaetes?14.4%?and Tenericutes?9.8%?are the dominant bacteria in the female samples of P.magnuspinnatus.Shewanella?14.94%?,Halomonas?18.92%?,Acinetobacter?4.88%?and Aeromonas?3.38%?of the phylum Proteobacteria are dominant genera in sample groups,and account for 62.13% of the ten dominant genera.However,Soonwooa,which belongs to the phylum Bacteroidetes,is higher in the B.pectinirostris male gut samples than that in the other groups.Cetobacterium of the phylum Fusobacteria is the most abundant genus in the B.pectinirostris female gut.Candidatus Arthromitus and Blautia of the phylum Firmicutes show the highest abundance in P.magnuspinnatus male samples,while unidentified chloroplast of the phylum Cyanobacteria is the most abundant in P.magnuspinnatus female samples.These results suggested that the most dominant phylum and genus were similar in different groups,but each species or gender group also have their unique bacterial structure.Further ? diversity analysis shows that the gut microbial diversity of B.pectinirostris with the herbivorous partial omnivorous food habits is lesser than that of P.magnuspinnatus with the omnivorous partial carnivorous food habits.In addition,there is no significant difference in the intestinal microbial diversity of B.pectinirostris between male and female samples?p>0.05?,while for P.magnuspinnatus,intestinal microbial diversity of male samples is significantly larger than that of female samples?p<0.05?.? diversity analysis?including PCo A and UPGMA?show that the male and female samples of B.pectinirostris cluster together,and the male and female samples of P.magnuspinnatus cluster together indicating that the effect of diet on the microbial community structure is more obvious than that of sex and imply that the difference of ecological niche between species?B.pectinirostris and P.magnuspinnatus?is greater than that within the species.