| The sedimental environment,abundance and biomass of meiofauna,community structure and biodiversity and systematics of nematodes,were quantitatively studied at a grid of 17 stations during the cruise of investigation in the subtidal zone of Bohai Bay,China from July to August and from October to November 2020.Meanwhile,the phylogenetic status and phylogenetic relationships of the the higher order metazoan major taxa of nematodes were investigated.The main results are as follows:A total of 7 groups of meiofauna in Bohai bay:Nematoda,Copepoda,Polychaeta,Ostracoda,Gastrotricha,Oligochaeta and Turbellaria.Free livingmarine nematodes are the most dominant group.The average abundance,biomass and production of meiofauna are2122.99 ind/10 cm2,2383.56μg dwt/10 cm2and 21452.08μg dwt/10 cm2·a in summer and those are 1812.62 ind/10 cm2,2060.06μg dwt/10 cm2and 18540.53μg dwt/10 cm2·a in autumn.Nematodes are the most dominant group,accounting for 91.04%in summer and93.11%in autumn of the abundance of meiofauna.The average abundance,biomass and production of nematodes are 1954.06 ind/10 cm2,781.62μg dwt/10 cm2,7034.61μg dwt/10 cm2·a in summer and those are 1687.80 ind/10 cm2,681.37μg dwt/10 cm2,6132.34μg dwt/10 cm2·a in autumn.Compared with other studies,the results of the present study are in the same magnitude.The interaction of environmental factors led to a mosaic distribution of meiofaunal abundance,which generally showed a gradual decrease from nearshore to offshore.Organic matter pollution at stations JYC05 near the mouth of the Ji Canal and BHB04near the mouth of the Shuanglong River in summer;the N/C ratios at stations JYC05,BHB04 and BHB35 in autumn are between 50 and 100,indicating eutrophication of the sea at these three stations.From the evaluation of ecological quality,most of the stations are in good condition.The environmental quality of the offshore sea is the best,followed by the nearshore sea and the worst in the estuary.From the seasonal point of view,the marine sedimentation environment is better in autumn than in summer.A total of 113 species or taxonomic entities of nematodes,belonging to 2 orders,6phyla,13 families and 84 genera,are identified during the summer cruise in Bohai Bay.In autumn,a total of 105 species or taxonomic entities are identified,belonging to 2 orders,5phyla,15 families and 75 genera.The following dominant species were obtained in summer:Dorylaimopsis rabalais,Thalassironus bohaiensis,Oxystomina elongate,Sabatieria alata,Paranticoma tricerviseta,Daptonema alternum,et al.In autumn,the following dominant species were obtained:Dorylaimopsis rabalais,Thalassironus bohaiensis,Oxystomina elongate,Daptonema alternum,Paranticoma tricerviseta,Sabatieria alata,et al.The mean richness index（d）,evenness index（J’）,diversity index（H’）and dominance index（λ）were6.4458,0.8341,3.1018 and 0.0720 in summer,and 6.1586,0.8147,2.9749,0.0839 in autumn,respectively.Richness index（d）,evenness index（J’）and diversity index（λ）and diversity index（H’）of nematode communities in summer were higher than those in autumn,while the dominance index（λ）was high in autumn.It indicated that more different species were present in the summer community with higher species richness and diversity.In contrast,a few species were relatively abundant in the autumn community,showing a higher degree of dominance.According to the nematode K-dominance curves,the BHB40 station dominance is the lowest in summer and autumn,but the highest diversity,a result consistent with the findings of univariate parameters.The MDS and the CLUSTER analysis show that the nematode community can be divided into four station taxa at 40.13%similarity in summer and39.41%similarity in autumn,which were group A:offshore stations;group B nearshore stations;group C Yellow River estuary stations;and group D central stations.The differences between the four station groups divided by nematode community species abundance matrix and between any two groups are confirmed to be significant by the One-way ANOSIM test in both seasons.BIOENV analysis show that the best combination of environmental factors to explain the structural characteristics of nematode communities in summer are:WT,CODMn,SCC and in autumn are:WD,OM,D50,SCC.This study investigates the basic taxonomic composition of nematodes in Bohai Bay by classical taxonomic means and gives a list of 113 nematode species,belonging to 2orders,8 phyla,35 families and 84 genera,which enriches the knowledge of species diversity of nematodes in Bohai Bay and even Bohai Sea.This paper describes seven new nematode species found in Bohai Bay,namely,Perspiria macramphida Zhai,Shi,Li&Sun,2023;Perspiria major Zhai,Shi,Li&Sun,2023;Amphimonhystrella boucheri Zhai,Geng&Sun,2022;Paramonohystera gracilis gracilis Zhai,Geng&Sun,2022;Perspiria brevicauda sp.nov.;Spirinia acuta sp.nov.and Spirinia boucheri sp.nov.On the basis of accurate taxonomy,this study also combined 18S rDNA sequencing analysis to analyze the phylogenetic status and phylogenetic relationships of the major taxa of nematodes of higher order.25 18S rDNA sequences of nematodes from different taxa are extracted from the sediment samples in Bohai Bay,and based on these sequences,combined with 110 sequences retrieved from Genbank and downloaded from their same or similar genera,we used the maximum a molecular phylogenetic tree of nematode 18S containing 135 sequences from different taxa is established by Maximum Likelihood method.It is found that the monogamous nematodes of the order Monogamidae are more closely related to the nematodes of the family Hiaridae;regarding the phylogenetic relationships of nematodes of higher order,the linear nematodes may be a transitional group in the evolution of taxa such as the thin pharynx and the chaetognaths to the monogamous order;the order Triplonchida is more inclined to be a subclass of the mouth spines;The Triplonchida is more likely to be a subclass of the Mouth Spines.The present study is intended to provide a solid and reliable basis for meiofauna and the cataloguing and species diversity of marine nematodes in China. |
