| Sandy intertidal zones were seasonally investegated for meiofauna abundance, biomass and group compositon in April, July and October 2010, and January 2011 in Dashali, Zhoushan (Zhejiang, China). In order to analyse the vertical and horizontal (between sections and among tide zones) meiofaunal distribution patterns, and the seasonal dynamics of meiofauna, samples were collected along two transects at high, mid and low tide zones, respectively.The dominant sediment types of the sampling stations were medium sand (MS) and fine sand (FS). The degree of sorting was very good. The average content of chlorophyll a (Chl-a) in the sediment was 0.0165 mg/kg. The average content of total organic carbon (TOC) is 0.0957%. The content of Chl-a and TOC was highest in autumn, lowest in winter. Results of PCA showed that skewness (SKcp) of the sediment, interstitial water temperature, content of oxygen, Chl-a, TOC and interstitial water salinity are the most important environmental factors.26,670 individuals of seventeen higher meiofauna taxa were recorded, including Nematoda, Copepoda, Turbellaria, Gastrotricha, Tardigrada, Polychaeta, Hydrozoa, Rotifera, Insecta, Amphipoda, Ostracoda, Halacaroidea, Kinorhyncha, Bivalvia, Gastropoda, Isopoda and Others.The most common taxa were Nematoda, Copepoda, Turbellaria, Gastrotricha, Tardigrada, Polychaeta and Hydrozoa (98.4% of total meiofauna abundance). Among the tide zones, number of major meiofauna taxa was largest in high tide zone, and was lowest in low tide zone. Among the seasons, number of major meiofauna taxa was lowest in spring.Average abundance of total meiofauma in the year was 768.38±381.43 ind./10cm2, average biomass of total meiofuana was 1646.64±881.56μg·dwt·10cm-2. Abundance of total meiofauma in the seasons were:578.70±395.07 ind./10cm2 in spring,1042.77±459.76 ind./10cm2 in summer,1115.76±511.41 ind./10cm2 in autumn, 303.85±167.53 ind./10cm2 in winter. Abundance was highest in autumn and summer, and lowest in winter. There was significant difference among seasons (One-Way ANOVA, p<0.01). Seasonal variation of abundance of Turbellaria and Tardigrada was the same as total meiofauna abundance. Abundance of Hydrozoa and Rotifera was also highest in autumn. Number of Turbellaria individuals was equal to 17.3% of total meiofauna individual number, this made abundance of autumn the highest of the year. Unlike Turbellaria, abundance of Nematoda, Copepoda, Gastrotricha and Polychaeta was highest in summer.There was significant difference of total meiofauna abundance among seasons (One-Way ANOVA, p<0.01). In spring, summer and autumn, total meiofauna abundance was highest in high tide zone, and lowest in low tide zone, but in winter it was in the opposite way. Seasonal variation of total meiofauna biomass was almost the same. Nematoda, Copepoda, Turbellaria, Gastrotricha and Tardigrada were the 5 most abundant taxon, they tend to be most abundant in the high tide zone.Nematoda, Copepoda, Turbellaria and Gastrotricha were the four most abundant taxon in this study, they were sorted from almost of sites in every season. The Cumulative Percentage of them at every station in every season is up to 71.58%～98.83%. Nematoda and Turbellaria were the two most abundant meiofauna taxon, the Cumulative Percentage of their relative abundance at every station in every season is up to 62.76%～89.36%. With the decreasing of Nematoda relative abundance, that of Turbellaria is always increasing, this is observed at different levels, such as seasons, tide zones and stations in every season..In each tide zone, the most abundant taxa was not the same:In high tide zone, the most abundant taxa was Turbellaria, while in mid and low tide zone, the most abundant taxa was Nematoda. Relative abundance of taxa is always not the same in different tide zones:relative abundance of Nematoda and Hydrozoa were highest in low tide zone and lowest in high tide zone, while relative abundance of Turbellaria and Gastrotricha was highest in high tide zone and lowest in low tide zone.In each season, the most abundant taxa was not the same:In spring and summer, the most abundant taxa was Nematoda. In autumn and winter, the most abundant taxa was Turbellaria. Relative abundance of taxa is always not the same in different seasons:relative abundance of Nematoda and Copepoda was highest in spring and summer, lowest in autumn. But relative abundance of Turbellaria and Hydrozoa was highest autumn and winter, lowest in spring. Average total meiofauna abundance in each depth layer was highest in the top layer, and became less and less in deeper layer. But there was no obvious vertical distribution of rules to follow in every site in each season. Nematoda, Gastrotricha and Tardigrada were most abundant in the surface layer, decreasing with increasing depth. Copepoda, Turbellaria and Hydrozoa, was most abundant in the subsurface layer from the top. Turbellaria was least abundant in the deepest layer, while Copepoda and Hydrozoa were least abundant in the surface layer. The six taxa above are recorded in every depth layer. In the vertical direction, Copepoda distribution is the most uniform, while Tardigrada, Rotifera, Gastrotricha and Ostracoda were the least uniform ones.Result of MDS ordination (at taxa level) shows that meiofauna communities in the same seasons, had the greater similarity. In every season, variation of meiofauna communities in high tide zone was larger than mid and low tide zone. Results of Cluster shows that in every tide zone, seasonal variation was obvious. In each season, meiofauna communities in the same tide zone always had greater similarity. Results of BIOENV showed that the combination of TOC, Chl-a, dissolved oxygen, MDφand QDφcan best explain the variation of meiofauna communities. |
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