Ecology Of Benthic Meiofauna In The Spawning Ground Of Anchovy In The Southern Yellow Sea, China

Abundance and biomass of meiofauna, community structure and biodiversity of free living marine nematodes, benthic habitat of meiofauna were quantitatively studied at a grid of 22 stations during the cruise of investigation for spawning ground of anchovy (Engraulis japonicus) in the Southern Yellow Sea, China in June 2003. The main results are as follows:The sediment types of the sampling stations mainly belong to silt-clay (TY) or sand-silt-clay (STY). Sediment characteristic parameters have significant correlations with each other. The average content of chlorophyll α (Chl-α) in 0-2cm sediment, 2-5cm sediment and 5-8cm sediment are (0.9285 ±0.5751) mg/kg, (0.5821 ±0.3552) mg/kg and (0.4107 ± 0.2863) mg/kg, respectively. The average content of phaeophorbide α (Pha-α) in 0-2cm sediment, 2-5cm sediment and 5-8cm sediment are (2.1043±1.4156) mg/kg, (1.5187+1.1370) mg/kg and (1.1032 + 0.8180) mg/kg, respectively. The horizontal and vertical distribution patterns of Chl-a and Pha-α are similar, indicating they have the same origin, i.e. they come from the benthic algae and the deposition of planktonic algae. The average content of organic matter is (2.64 +1.93) %. Spearman rank correlation analysis shows that water depth, bottom water temperature, water content, silt, clay percentage and Mdo are the important factors which affect the organic matter and pigments content.A total of 18 groups of meiofauna: Nematoda, Copepoda, Polycheata, Ostracoda, Kinorhyncha, Bivalve, Gastropoda, Gastrotricha, Turbellaria, Halacarida, Tanaidancea, Cnidaria, Callianassa, Amphipoda, Insecta, Amphiura, Cumacea and others are identified. Free living marine nematodes are the most dominant group, accounting for 88.65% of total abundance of meiofauna, with benthic harpacticoid copepods in the second, accounting for 5.84%. The mean abundance, biomass and production of meiofauna are (1584±686) ind.10cm~-2, (1031.7 + 415.1) μg dwt 10cm~-2 and (9285.5±3736.3) ug dwt 10cm'2 a'1, respectively. Compared with other studies, the results of present study are in the same magnitude.In terms of vertical distribution, 65.88% of total meiofauna is found in the surface sediment (0-2cm), 27.66% in 2-5cm sediment and 6.47% in 5-8cm sediment. The mean abundance of nematode is (1404 + 670) ind.lOcm'2, with 61.4% in 0-2cm sediment. And 83.8% of copepod is in 0-2cm sediment. The vertical distribution pattern is similar to that in the Bohai Sea and the Jiaozhou Bay. In terms of horizontal distribution, the stations near the coast have higher abundance and biomass of meiofauna. In terms of size distribution, 91.12% is between the size of 500um and 50um and 8.88% is between 50um and 31 urn. Correlations between meiofauna, nematode and environmental factors analysis show that Chl-a is the key factor that affects the distribution of meiofauna.The trophic structure of free living marine nematodes is studied. It includes selective deposit feeders (1A) 67 species, non-selective deposit feeders (IB) 71 species, epigrowth feeders (2A) 71 species and predators/omnivores (2B) 23 species. The deposit feeders (1A and IB) are dominant by total species number (138 species) and average species number per station (58.79%), while epigrowth feeders (2A) are over 30%, which shows the food source of nematodes is mainly detritus and there are abundant benthic diatoms in the sampling areas. The juveniles of nematodes are 51.20% and the ratio of female/male is 1.05:1. It is similar to other studies.A total of 232 species or taxa of free living marine nematodes, belonging to 149 genera, 35 families and 4 orders, are identified. The dominant species in the sampling area are: Dorylaimopsis rabalaisi, Microlaimus sp, Promonhystera sp, Leptolaimus sp > Prochromadorella sp, Cobbia sp. 1, Chromadorita sp, Daptonema sp, Campylaimus sp.l. Paramonohystera sp, Quadricomasp.lt Aegialoalaimus sp, Halalaimus sp.2, Parasphaerolaimus sp, Parodontophora marina0The community structure of nematode is studied. CLUSTER analysis and MDS analysis divide the sampling stations into three types of communities (or station groups). They are I: Coast Community, II: Transitory Community between Coast and YSCWM, and III: YSCWM Community. The Coast community includes twosub-groups: IA: Rongcheng and Haizhou Bay Coast Community and IB: Jiangsu Coast Community. One-Way ANOSIM test shows that the community structures of different station groups are significantly different. The trophic structure and biodiversity analysis of the nematode community also proves the division of station groups. Correlations analysis between the nematodes community and environmental factors shows that water depth, water content, organic matter, Chl-a and Pha-a, Mde, clay percentage (%) and bottom water temperature are the important factors. The best combination of environmental factors, which can explain the nematodes community structure, is water depth, water content and organic matter.