| Paper analyze the differences between abiotic factors(temperature,salinity and the maximum of submerged depth)and biological factors(vegetation,zooplankton,benthic macro-invertebrate and nekton)in the three subhabitats and explored the selection on the subhabitats and differences of diet compositions for Acanthogobius ommaturus base on the monthly survey from July 2015 to June 2016 at the creek,mudflat and Scirpus mariqueter salt marsh of Dongtan wetland of the Yangtze estuary.The main research results as follows:(1)Differences between abiotic and biological factors in the three sub habitatsThe maximum of submerged depth in the tidal creeks was significantly higher than that in the mudflat and the Scirpus mariqueter salt marsh.There was no significant difference in water temperature and salinity between the three subhabitats(ANOVA,P>0.05).From the end of spring to the beginning of autumn(May-October),it is a period of vigorous growth of Scirpus mariqueter.From late autumn to early spring(October-March),it gradually withers,and in March spring,it begins a new round of growth.During the survey,71 species of zooplankton were recorded,belonging to 22 orders.Among them,the aphid,the Diplostraca sp.,the Cyclopoidea sp.,the Harpacticoida sp.and the Calanoida sp.were dominant in quantity,reaching 94.5% of the total.There are 33 species of benthic macro-invertebrate,belonging to 15 families,with crustaceans(7 species)and mollusks(6 species)predominating.There are 32 species of nekton,belonging to 17 families,with the largest number of Cyprinidae sp.and Palaemonidae sp.(both of which are 5 species),followed by Gobiidae sp.and Grapsidae sp.(both of which are 4 species).There was no significant difference in the distribution of plankton in the three subhabitats,but there were significant differences in the composition and dominant species of benthic macro-invertebrate and nekton.The dominant species of the benthic macro-invertebrate assemblages in the creek and the Scirpus mariqueter salt marsh are the Ilyoplax deschampsi,the Corbicula fluminea and the Stenothyra glabra;In addition to the dominant species,Notomastus latericeus and Sinonova culaconstricta are dominant species in the mudflat.The number of benthic macro-invertebrate species in the Scirpus mariqueter salt marsh is the most abundant,followed by the creek and the lowest number of species in the mudflat.A total of 23 species of nekton were captured in the creek.The dominant species were Chiromantes dehaani,Exopalaemon annandalei,Acanthogobius ommaturus,Liza haematocheila and Helice tientsinensis.A total of 26 species of nekton were captured in the mudflat.The dominant species were Pelteobagrus nitidus,Lateolabrax maculatus and Coilia ectenes.There are 17 species of nekton captured in the Scirpus mariqueter salt marsh.The dominant species are Lateolabrax maculatus,Liza haematocheila,scorpionfish,Acanthogobius ommaturus,Coilia ectenes and Saurogobio dumerili.Through Bray-Curtis similarity cluster and non-metric multidimensional scale(nMDS)analysis,it is found that zooplankton assemblage can be roughly divided into summer and other seasons;the benthic macro-invertebrate assemblage in three subhabitats has similar similarity,and the benthic macro-invertebrate assemblage in the Scirpus mariqueter salt marsh is similar to that in the creek,but it is quite different from the mudflat.The nekton assemblage can be roughly divided into two groups: winter/ spring and summer/autumn.(2)Differences of diet compositions of Acanthogobius ommaturusAcanthogobius ommaturus mainly feeded on shrimp(IRI(%)= 43.74),crab(IRI(%)= 39.10),insects(IRI(%)= 5.45),and polychaete(IRI(%)= 4.49).Wait for 30 small class of 10 categories food organisms.Shrimp and crab are the main food organisms for the Acanthogobius ommaturus,and the dominant species are the Palaemon sp.,the Sesarma sp.and Corixidae sp.,such as Exopalaemon annandalei and Micromecta quadriseta.Acanthogobius ommaturus increased the food intake in the autumn in preparation for wintering.The average P(%)and average feeding level of each month fluctuated greatly,which was the lowest in July and the highest in November.The average feeding level of Acanthogobius ommaturus increased significantly with the increase of body length,indicating that the feeding ability of small individuals was lower than that of large individuals.(3)Selection on the subhabitats of Acanthogobius ommaturusSamples of t Acanthogobius ommaturus were collected from June to November,and the proportion of the sample juveniles was as high as 96.9%.A total of 93 Acanthogobius ommaturus were collected in the creek,which were 5.2 and 4.9 times that of the mudflat and the Scirpus mariqueter salt marsh,indicating that the creek is one of the main channels for the squid to enter the intertidal wetland.During the investigation period,the diurnal difference between the tail and tail of the creek and the Scirpus mariqueter salt marsh was small and not significant(ANOVA,P>0.05),and the diurnal abundance of the Acanthogobius ommaturus was higher than that of the mudflat and the Scirpus mariqueter salt marsh.Different sources of feed in different habitats are responsible for the large difference in the day-night difference between the feeding intensity and the type of bait in the mudflat and the Scirpus mariqueter salt marsh.The food composition of Acanthogobius ommaturus in different subhabitats is quite different.The W% value of fish in the food composition of the squid in the mudflat is the highest,and the W% value of the fish in the sea sedge is only 0.71%.The W% value of the crab in the sea sedge is the highest..The results of clustering and sorting indicated that the food composition of the goby fish in the Scirpus mariqueter salt marsh was relatively different from that of the other two subhabitats.The food composition of the Scirpus mariqueter salt marsh was also specific.However,the dominant bait in a single subhabitat is not enough to meet the feeding needs of the Acanthogobius ommaturus.The increase in the biological abundance of the larger baits of other individuals has a greater impact on the food composition of Acanthogobius ommaturus,and it is most likely to pursue the bait organisms and enter the mudflat and the Scirpus mariqueter salt marsh.According to the results of CCA analysis,the density of Scirpus mariqueter has a great influence on the distribution and feeding of the Acanthogobius ommaturus.It shows that salt marsh vegetation has a strong role in increasing the heterogeneity of fish habitats and providing food sources.The heterogeneity of the terrain and the resulting differences in biological distribution lead to different effects of the same environmental factors on fish feeding in different subhabitats.Habitat modeling experiments show that the abundance of the Acanthogobius ommaturus in the creek is about 10 times that of the mudflat and the Scirpus mariqueter salt marsh,and it is preliminarily verified that it enters the intertidal zone mainly through the creek,which enters the mudflat and the Scirpus mariqueter salt marsh.The main reason to enter the mudflat and the Scirpus mariqueter salt marsh is feeding.Therefore,from the perspective of habitat utilization,this study speculates that Acanthogobius ommaturus preferentially enters the intertidal zone through the rising water of the creek,and then spreads to the salt marshes or the mudflat for predation or evading predator;The difference in the abundance of Acanthogobius ommaturus is related to the difference in the distribution of the food intake in different subhhabitats. |
