Community Structure And Distribution Of Meiofauna In The Yellow Sea And East China Sea In Summer

Meiofaunal group composition, abundance, biomass and spatial distribution were investigated based on samples collected from 33 stations in July 2008 and from 15 stations in June 2009 in the Yellow Sea and 18 stations in the East China Sea in June 2009. The biodiversity and community of free-living marine nematode were investigated based on samples collected from 33 stations in the Yellow Sea in July 2008 and analyzed in relation to benthic environmental variables.The sediment types comprised silt (18 stations), clay-silt (13 stations) and sand-silt (2 stations). The average content of water, organic matter, chlorophyll a and phaeophytin a was (40.1±9.3)%, (0.9±0.4)%, (0.6±0.4) mg·kg-1 and (1.9±0.9) mg·kg-1 respectively. And there was no significant change in the organic matter content in surface (0~2 cm), subsurface (2~5 cm) and bottom (5~8 cm), where the content was on average (1.0±0.5)%, (0.9±0.4)% and (1.0±0.4)% respectively. Chlorophyll a and phaeophytin a were especially rich in the surface sediment, while those in the subsurface were nearly as many as that in the bottom.A total of 16 groups of meiofauna were sorted at the 33 stations in the Yellow Sea in July 2008, and free-living nematodes was the dominant group, followed by Copepoda, Cumacea, Kinorhyncha, Polycheata and so on. The average abundance of meiofauna was (1375±793) ind·10 cm-2 and the biomass was (1203±707)μg dwt·10 cm-2. There was no significant change in group composition in 2009 (15 stations) when compared that in 2008 in Yellow Sea. The average meiofaunal abundance and biomass in the Yellow Sea (15 stations) in 2009 were (3677±2126) ind·10 cm-2 and (3211±1980)μg dwt·10 cm-2, respectively, both values were increased when compared to those in 2008. The average abundance and biomass of meiofauna in the East China Sea (18 stations) in 2009 were (1140±675) ind·10 cm-2 and (1058±627)μg dwt·10cm-2, respectively. The meiofaunal horizontal distribution was heterogeneous. In terms of vertical distribution, the meiofauna were mainly distributed in the surface sediment, accounting for 88% of total abundance in the Yellow Sea in 2008, 77% in the Yellow Sea in 2009, and 74.0% in the East China Sea in 2009. A total of 294 species/taxonomic units of nematodes were identified, belonging to 110 genera, 27 families and four orders. The average values of species richness (d), diversity index (H'), evenness index (J') and dominance index (1-λ) of nematodes were respectively 6.90, 2.90, 0.87 and 0.92. The name list of free-living marine nematodes identified was given (refer to Appendix). The first ten dominant species were Dorylaimopsis rabalaisi, Dorylaimopsis sp. 4, Sphaerolaimus sp. 7, Sabatieria sp. 8, Parodontophora marina, Paramesacanthion sp. 3, Daptonema sp. 10, Chromadora sp. 2, Vasostoma longispicula, and Paramarylynnia filicaudata.There were four types of nematodes in the Yellow Sea in July 2008: epistrate feeders (2A) occupying 36.3% of total nematode abundance, deposit feeders (1B) occupying 29.8%, selective deposit feeders (1A) occupying 19.2%, and, predators/omnivores (2B) occupying 14.70%. Individual nematodes were identified as females, males and juveniles. Generally juveniles accounted for 31.3% of total nematode abundance. The ratio of females to males was about 1.5:1. Free-living nematodes in the Yellow Sea could be divided into three communities based on CLUSTER analysis: northern Yellow Sea cold water mass community, Yellow Sea cold water mass community and mixed community. ANOSIM test indicated significant difference between each two communities (P<0.05). Statistical analyses suggested that nematode abundance had negative correlation with the content of phaeophytin a. Results of BIOENV analysis showed that a combination of Ph a content and organic matter content was most relevant to explain nematode species composition and diversity (Spearman correlation coefficient was 0.192). The content of Ph a and organic matter as well as the temperature and salinity were the most important factors in regulating the nematode community and diversity.Moreover, five new species of nematode were described. Vasostoma longispicula Huang and Wu is characterized by its large size, amphideal fovea with two and a half turns, slender and bent spicules, 15~17 tubular precloacal supplements, one precloacal seta, and gubernaculum with slender dorso-caudal apophyses. Vasostoma articulata Huang and Wu is characterized by its thin and long body, pharyngeal bulb pyriform, double-jointed curved spicules. This new species can be easily identified by the articulated spicules and the pyriform pharyngeal bulb from two other species V. longispicula and V. spiratus. Paramonohystera eurycephalus Huang and Wu is characterized by relatively wide head diameter (33μm in width), large cup-shaped buccal cavity; presence of numerous long cervical setae; gubernaculums tubular with a distal hook; and tail with three long terminal setae (up to 36μm). Steineria sinica Huang and Wu is characterized by eight groups of three subcephalic setae at almost same level as cephalic setae; eight groups of two long cervical setae situated between subcephalic setae and amphidial fovea; spicules slender, cephalate proximally and taper distally; gubernaculum pipe-shaped with dorso-caudal apophysis. Vasostoma brevispicula is characterized by its thin and long body, tubular buccal cavity with three small projections, long pyriform pharyngeal bulb, amphideal fovea with two and a half turns, spicules curved with central lamella.