The Study On The Community Of Free-living Marine Nematodes In The Northern Beibu Gulf, China

Free-living marine nematodes are numerically the dominant group of the meiofauna,and are the most abundant metazoans in marine sediments.They distribute all over the world.Nearly all free-living marine nematodes are considered to be forever members of the meiofauna.The term "meiofauna" in this study refers to metazoans that pass through a 1 or 0.5 mm mesh sieve but are retained on a 0.042 or 0.031 mm sieve.They had short life cycle,fast turnover and high productivity.Marine nematodes inhabit sediment lifetime,can endure extensive salinity,temperature, hypoxia tolerance,high stain resistance,low natural mortality,and low respiratory loss.Population distribution has been obvious related to habitat.The diversity index and community variation can be a useful method for environmental monitoring. Marine nematodes play an important role in nutrient recycling and energy flow of whole benthic ecosystem.So,marine nematodes are good experiment research materials.Our lab have been studied the microfauna since 2006,and published related paper in 2008 for the first time.Based on our previous research,we choose the 23 stations of free-living marine nematodes,the dominant group of microfauna in the northern Beibu Gulf,used high definition microscope and photo technique,classifed the marine nematodes to genera level,and learned the trophic structure,community structure and the relationships with sediment environment factors.It can be provided the basic materials for perfecting benthic community and ecosystem health evaluation system in Beibu Gulf.The main results are as follows:Community compostition of marine nematodes.A total of 83 free-living marine nematodes genera,belonging to 27 families and 3 orders,were identified. Dorylaimopsis(16.45%),Sabatieria(12.31%),Sphaerolaimus(6.84%), Parodontophora(5.77%),Setosabatieria(5.20%),Cheironchus(3.65%), Metadesmolctimus(3.52%),Elzalia(3.44%),Desmodora(3.38%),Paracomesoma (3.19%),Terschellingia(3.17%),Ammotheristus(2,92%),Syringolaimus(2.04%), Oxyonchus(2.03%),Halalaimus(1.80%).Dorylaimopsis,Sabatieria,Parodontophora and Sphaerolaimus were the dominant genera.Trophic structure and sex ratio.Epigrowth feeders were the dominant type for the highest genera numbers and quantity.It can be concluded that benthic diatom and organic oddment were the main food source in the northern Beibu Gulf.The ratio of female to male of marine nematodes was 1.45 to 3.35,male had more quantity than female.Genera level diversity of marine nematodes community.Diversity indices were between 2 and 3 in most stations.Community structure analysis of marine nematodes showed that B16 station in winter had the highest dominance and the lowest diversity, deviate other stations in MDS Ordination graph,and B3 station in spring had the lowest dominance and the highest diversity.The main environmental factors affecting on marine nematodes community. Temperature and bottom water dissolved oxygen were the important factors to affect community biodiversity of marine nematodes in spring,chlorophyll was the important factor to affect community structure in autumn,silt,sand and median diameter were the important factors to affect evenness and dominance community structure in summer.The main environmental factors affecting on the abundance of dominant genera of marine nematodes.The relationships analysis between common genera of marine nematodes and environmental factors showed that,Dorylaimopsis,Sabatieria, Parodontophora and Sphaerolaimus were eurytopic genera,they had strong viability, and were not affected by environmental factors,such as depth of water,temperature etc.But bottom water dissolved oxygen,chlorophyll and pH had certain effect on them,medium grain-size had very significant relationships with the most important genera Dorylaimopsis and Sabatieria.The northern Beibu Gulf was silt-clay substrate, and suitable for this two dominant genera's habitat.