Ecology Of Meiofaunal Assemblages In The Intertidal Zone Along The Southeastern Coasts Of China And Notes Of New Species And New Record Species Of Marine Nematodes

Meiofauna is a high-quality food for many economic fish,shrimp and shellfish at larval stage.It is an important part of benthic food web.Meiofauna is sensitive to environmental changes,which makes meiofauna as an important indicator of marine environmental quality.According to the ternary method of sediment quality assessment,the ecology of benthic assemblage is an important part of environmental quality assessment.Free-living marine nematodes are the most dominant and important group of meiofauna.Understanding the assemblage ecology of marine nematodes in various habitats can further evaluate the environmental quality of study areas.In general,the background data of meiofauna in sandy,mangrove and muddy intertidal zone in China is still relatively scarce,there is a long way to discover,identify and describe new species of marine nematodes in various habitats of China.In this thesis,meiofaunal samples were collected in the intertidal zone of Eyuyu Island of Xiamen,in Xiatanwei artificial mangrove wetland,in the intertidal zone of Daya Bay and Beihai of Guangxi from 2018 to 2020.Three typical habitats of sandy beach,mangrove and mudflat of meiofauna samples were included,and the corresponding sediment samples were collected for the determination of environmental factors such as temperature,salinity,sediment grain size,chlorophyll a,phaeophyin,heavy metals and polycyclic aromatic hydrocarbons(PAHs).Combined with the historical data,meiofaunal assemblages in the intertidal zone of Southeast coast were analyzed,the relationships with environmental factors were discussed,the ecological characteristics of meiofauna were fully analyzed,which can enrich the data of meiofauna in the study areas.The main results were as follows:1)In sandy habitat,the density of meiofauna in the middle intertidal zone was higher than that in the low intertidal zone;the density of meiofauna was the highest in spring,followed by winter,and lower in autumn and summer;high density of Harpacticoida was present.The main feeding types of marine nematodes were nonselective deposit feeder 1B and epigrowth feeder 2A,which mainly feed on small particulate organic matter and diatoms.The dominant genera of marine nematodes in the sandy habitat were Terschellingia,Paralongychatholaimus,Dorylaimopsis,Halichoanolaimus,Metachromadora and Axonolaimus.2)In mangrove habitat,the number of Oligochaeta was significantly higher than that in sandy and muddy beaches.The dominant feeding type of marine nematodes were non-selective deposit feeders 1B,which meant that most of the marine nematodes feed on decaying organic debris in the mangrove habitat of Southeast China.Terschellingia,Sabatieria,Parodontophora,Spilophorella,Daptonema,Anoplostoma and Viscosia were the typical dominant genera of marine nematodes in the mangrove habitats of Southeast China.However,Daptonema was scarce in some mangroves such as Sonneratia apetala and Avicennia marina,probably because it was sensitive on some substances in the sediment of these mangroves.3)In muddy habitat,the density of meiofauna and marine nematodes in the mudflat habitat was generally higher in spring and lower in summer;compared with mangroves,the number of Oligochaeta in the mudflat decreased.Daptonema and Terschellingia were the most typical genera of marine nematodes in the mudflats.Sabatieria was highly distributed in mudflats,but less in mangroves according to the data from Xiatanwei and Daya Bay.For feeding types of marine nematodes,nonselective deposit feeder 1B was dominant in both Xiatanwei and Daya Bay.4)The most important environmental factor affecting the marine nematode assemblages was the composition of particle size in the sediment in the intertidal zone.Sabatieria was negatively correlated with silt,and Terschellingia was negatively correlated with Cr content,suggesting that Sabatieria may be sensitive to Cr.Daptonema,Parodontophora and Steineria were probably PAHs resistant genera.5)According to the threshold values of organic matter,heavy metals or polycyclic aromatic hydrocarbons,the environmental quality of Eyuyu Island in Xiamen,Xiatanwei in Xiamen,Daya Bay and Beihai belonged to "high" or "good"grades;according to the thresholds of maturity index,C-P value,Shannon-Wiener diversity index and trophic diversity index,the results showed that in Eyuyu Island,some stations in autumn and spring belonged to "good";while some stations in summer belonged to "poor".The results showed big variation of grades in Xiatanwei.In spring,the mangroves in Daya Bay belonged to "moderate",while the mangrove edge and mudflat in Daya Bay belonged to "poor" or "bad" grade.In summer,mangroves and beaches in the Beihai belonged to "moderate",while the mudflat in Beihai belonged to "poor".The environmental quality in most mangrove habitats was better than that in the mudflat habitats.In the four seasons,the environmental quality in summer was generally poor.In the evaluation of ecological quality,we should mainly consider more of the biological variables such as maturity index,C-P value,Shannon-Wiener diversity index and maturity index.6)In this thesis,4 new species and one new record species of marine nematodes were described in the intertidal zone along the Southeastern coast of China,which were as follows:Parasphaerolaimus jintiani Fu,Boucher&Cai,2017(new species);Sphaerolaimus callisto Zograf,Pavlyuk,Trebukhova&Nguyen,2020(new record);Sabatieria longispicula n.sp.(new species);Tripyloides mangrovensis Fu,Zeng,Zhou,Tan&Cai,2018(new species);Tripyloides amoyanus Fu,Zeng,Zhou,Tan&Cai,2018(new species).Our results can provide important basic data for the study of meiofauna in the intertidal zones and a scientific basis for the protection,development and utilization of intertidal zones in the context of global climate change.