| The meiofauna was quantitatively investigated in the sandy beach of Taiping Bay, Qingdao based on monthly sampling from Oct.2004 to Oct.2005. The sedimentary environment, abundance and biomass of meiofauna, community structure and biodiversity and systematics of free-living marine nematodes, were quantitatively studied at the middle intertidal zone during the periods of investigation. In spite of detailed variety across temporal and spatial scale, conservative bimodal metazoan benthic biomass size spectra were observed in different environmental condition. Sheldon-type and normalized biomass size spectra of metazoan benthos were constructed in the sandy intertidal zone. Seasonal variation of biomass size spectrum was analyzed using the data of the sandy intertidal zone. Secondary productions and oxygen consumptions of metazoan benthic assemblages were estimated by the method of continuous integral model. The main results are as follows:The dominant sediment types of the sampling stations are MS and FS, silt and clay contents were very low. The studied site is a typical sandy beach. Sediment characteristic parameters had significant correlations with each other. The average content of chlorophyll a (Chl-a) in the sediment was 0.396 mg·kg-1 sediment with low value in winter and high in summer and autumn. The average content of phaeophorbide a (Pha-a) in the sediment was low in the whole year, on average 0.045 mg·kg-1 sediment. The average content of organic matter was 0.304%. The highest value was 0.460% in spring and the lowest one was 0.133% in winter. Correlation analysis showed that sediment Chl-a content correlated with temperature positively, which suggests that the primary production is controlled by temperature and solar radiation. The average contents of the heavy metals Cr, Cu, Zn, As, Cd and Pb were 0.568μg /g, 1.240μg/g, 13.158μg/g, 3.748μg/g, 0.045μg/g and 3.156μg/g, respectively. The whole year contents of heavy metals at the studied site differed a lot. All the contents of heavy metals at the studied site were lower than the national standard, which means the Taiping Bay is still clean and not polluted by heavy metals. A total of 12 groups of meiofauna were identified at the studied site: Nematoda, Copepoda, Polychaeta, Bivalvia, Ostracoda, Amphipoda, Cumacea, Gastrotricha, Turbellaria, Oligochaeta, Halacaroidea and others. The average abundance of meiofauna was (1025.40±168.84) ind.10cm-2. Free-living marine nematode was the most dominant group, accounting for 89.16% of total abundance of meiofauna, with Polychaeta being the second, accounting for 3.91%.The mean biomass and production of meiofauna were (1195.87±476.53)μgdwt10cm-2 and (10762.80±4288.77)μg dwt 10cm-2 a-1, respectively. In terms of vertical distribution, 51.5% of total meibenthos was found in the surface sediment 0-4cm, 25.9% in 4-8cm and 10.0% in 8-12cm. The vertical distribution of meiofauna exhibited seasonal variation. In the summer months, meiofauna density decreased in the upper layers. In autumn, meiofauna concentrated in the upper layers and with the decreasing of temperature, they migrated to the deeper layers.A total of 77 genera of free-living marine nematodes, belonging to 23 families and 4 orders, were identified. The dominant genera in the sampling area are: Microlaimus, Bathylaimus, Neochromadora, Enoplolaimus, Metadesmolaimus, Theristus, Metoncholaimus, Axonolaimus, Ascolaimus, Paracanthonchus, Chromadorita, Promonhystera, Rhynchonema, Nannolaimus, Oncholaimus, Spiliphera, Paracyatholaimus, Tricoma, Camacolaimus, Paramonhystera, Chromadorita, Elzalia, Oxyonchus, Acantholaimus, Doliolaimus, Daptonema, Prochromadorella, Halalaimus. The average species abundance index, evenness index, diversity index and dominance index were 3.92, 0.63, 1.91 and 0.72, respectively.The trophic structure of free-living marine nematodes was studied. It included 29 genera of epigrowth feeders (2A), which accounted for 37% of the total genus number, 8 genera (11%) of selective deposit feeders (1A), 28 genera (36%) of non- selective deposit feeders (1B) and 12 genera (16%) of predators/omnivores (2B). Epigrowth feeders (2A) were dominant by total genus number and relative abundance, which showed the food sources of nematodes are mainly detritus and benthic diatoms in the sampling area. Juveniles accounted for 21.51% of total nematodes and female/male ratio was 1: 1.128. It is similar to other studies. The community structure of nematode was studied. CLUSTER and MDS analyses divided the sampling stations into two groups (or sampling months). They are A: spring and summer group, and B: autumn and winter group. One-Way ANOSIM test showed that the community structures of different season were significantly different. The trophic structure and biodiversity analyses of the nematodes community also proved the division of seasons. BIOENV analysis between the nematodes community and environmental factors showed that salinity, pH, Mdφ, and the content of Cd and Pb were important factors for the spring and summer nematode communities. The best combination of environmental factors, which can explain the autumn and winter nematodes community structure, were pH, organic matter content and the content of Cr, Cu and Pb.Structure of biomass size spectrum transformed seasonally. Sheldon-type biomass size spectra appeared tri-modal at January and April, but bimodal with a strong trough at July and October. Closely coupling between trough strength and DO suggested that species located in the size classes of trough might be more sensitive to hypoxia than those in other size classes. All normalized biomass size spectra fitted linear regression reasonably. Two different troughs, however, were revealed by analyzing standardized residuals of normalized biomass size spectra. Bottoms of troughs located respectively in 0 to 1 and 5 to 6 size classes. Therefore a hypothesis is set forth: DO is one of the reasons for conservative trough in benthic biomass size spectra, since meiofauna and macrofauna take different strategies to adapt hypoxia. At least the hypothesis is reasonable at the site examined in this study, because it can explain almost all the abnormal characters at the sandy intertidal zone.By the method of continuous integral model, secondary productions and oxygen consumptions of macro- and meiofuana were calculated in the sandy intertidal zone. Average of secondary productions of 4 seasons was 2.541 g dwt·m-2·a-1, and average of oxygen consumptions was 0.120 mmol·m-2·h-1 at the intertidal zone. Both secondary production and oxygen consumption showed positive correlations with intercept of normalized biomass size spectra. Compared with the method following the formula P = 9B, continuous integral model can provide more reliable evaluation of secondary production of meiofauna.
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