Study On Grain Size Composition And Food Source Of Gut Contents In Three Species Of Sipuncula

Sipuncula was a kind of marine invertebrates that living in burrows and feeding on the bottom of the sea.Throught the early observation of the intestinal anatomy of Sipuncula,that was found the intestinal contents of Sipuncula were mainly composed of various inorganic particles,debris of marine plants,shell fragments,echinoderm bone debris and various organic substances.Siphonosoma australe,Phascolosoma arccuatum and Sipunculus nudus belong to Sipuncula.They were three important species of Sipubcula in the tropical intertidal zone,rich in nutrients and of high economic value,so they become important local fishing species.Up to now,the research on these three species of Sipubcula has focused on artificial breeding,nutritional composition and biological efficacy analysis,and there are few articles on the food sources of Sipuncula.Based on this,this paper uses high-throughput sequencing technology to study the microbial community structure,food source and its relationship with the surrounding sediments of the above three economically valuable Sipuncula.The contents were as follows:1.Grain size and TOM analysis of gut contents and surrounding sedimentsThe main grain size components of the gut contents of Siphonosoma australe were125～250 μm and 63～125 μm(accounting for 41.33±2.15% and 27.33±1.09%,respectively),which were significantly different from the surrounding sediments of Siphonosoma australe(P < 0.05).No particles with a grain size of >1000 μm were found in the gut contents of Siphonosoma australe.The 125～250 μm grain size component(42.36±2.22%)was the highest in the gut contents of Phascolosoma arccuatum.No grains > 1000 μm were also found in the gut contents of Phascolosoma arccuatum.For Sipunculus nudus,although the main grain sizes of the gut contents and surrounding sediments were 250～500 μm and 125～250 μm,a significant difference in grain size between 250～500 μm and 125～250 μm(P < 0.05)was still visible.In addition,grains with a grain size > 1000 μm were found in the gut contents of Sipunculus nudus.2.Study on bacterial communities in gut contents and surrounding sediments of three species of Sipuncula.In this study,16 SrRNA gene and high-throughput sequencing technology were used to jointly analyze the bacterial community composition of gut inclusions and surrounding sediments of three species of Sipuncula.The results were as follows,with 12 prokaryotic phylums detected in 24 samples.Of the gut contents of the three species of Sipuncula,the most dominant phylum was the Buciformus;Among the surrounding sediments of Siphonosoma australe,Phascolosoma arccuatum and Sipunculus nudus,the relative abundance of Proteobacteria phylum was the highest(42.03%,45.43%,42.31%,respectively).The contents of the gut contents of the three species of Sipuncula were the highest(the relative abundances of the gut contents of Siphonosoma australe,the gut contents of Phascolosoma arccuatum and the gut contents of Sipunculus nudus were36.95%,22.33% and 43.94%,respectively).Proteobacteria is the second most abundant taxa(average 18.11%)of the gut contents of the three species of Sipuncula.The cyanobacteria phylum accounted for 11.04%,7.61% and 26.82% of the gut contents of Siphonosoma australe,Phascolosoma arccuatum and Sipunculus nudus,respectively.At the genus level,the content of Sulfurovum was highest in the sediments surrounding the three species of Sipuncula(average 4.36%),followed by Gp10,Gp22,and diatoms(>1%).Among the gut contents,the relative abundance of Gplla was highest(average 12.76%).NMDS and PCo A analysis were used to explain the relationship between bacterial communities in different samples.PCo A analysis based on Unweighted-Uni Frac distance revealed overlapping bacterial community composition of gut contents of the three species of Sipuncula,indicating that they had similar bacterial communities.The UPGMA tree showed that the gut samples of three different species of Sipuncula and their surrounding sediments were clustered into two groups,indicating that the gut contents of the three kinds of species Sipuncula were different from the bacterial community composition of the surrounding sediments.3.Comparison of eukaryotic food sources of three kinds of species of SipunculaIn this study,18 SrRNA genes and high-throughput sequencing technology were used to sequence and analyze the gut contents of three Sipuncula and their surrounding sediments to study the eukaryotic food sources of three kinds of species of Sipuncula.The results show that of all the identified gates,most are concentrated in 23 gates.The eukaryotic dominant phylum in the gut contents of Siphonosoma australe was Basidiomycota,Arthropoda,and Chlorophyta,while in the surrounding sediment the eukaryotic dominant phylum is Chlorophyta,Nematoda,and Bacillariophyta.The eukaryotic dominant phylum in the gut contents of Phascolosoma arccuatum was Chlorophyta,Basidiomycota,and Annelida,that the eukaryotic dominant phylum in the surrounding sediment is Annelida,Nematoda,and Bacillariophyta.The eukaryotic dominant phylum in the gut inclusions of Sipunculus nudus were Basidiomycota,Nematoda,and Chlorophyta,and the eukaryotic dominant phylum in the surrounding sediments were Nemertea,Annelida,and Bacillariophyta.At the genus level,Heteromastus was the highest in the sediments surrounding the three kinds of species of Sipuncula(average 12.36%).In gut contents,the relative abundance of Pleurotus was highest(average 38.50%).The results revealed the main food sources of the three kinds of species of Sipuncula and also reflected their feeding selectivity.