Ecological Studies On Zooplankton Community Structure And The Resting Eggs In Guangzhou Typical Waters

Zooplankton, as primary consumers, are an important group of organisms in aquatic ecosystems and a key link of food chains. They play significant roles in energy flow, material circulation, and information transfer. In the present study, a survey based on regular monthly sampling in 8 suburban small rivers(namely, the River 2, River 6, River 8, River 12, River 14, River 16, River 19, and River 21) was carried out from January to December in 2015 in the district Nansha, Guangzhou, China. Based on light microscopic identification, we analyzed the species composition and abundance of zooplankton, recruitment potential of resting eggs in the sediment, and the characteristics of water quality. Meanwhile, we compared the results with that obtained from other ponds, reservoirs, estuaries, lakes and rivers within the urban area of Guangzhou. The main results are highlighted as follows:1. In total, 63 species of zooplankton, including 14 species of copepods, 5 cladocerans, and 44 rotifers, were identified in the rivers of Nansha. The proportion of rotifers in the zooplankton community reached 61-90%. Species richness of zooplankton in the summer and autumn(51 species) was much higher than those in the winter and spring(38 species). The species Keratella cochlearis, K. tropica, Brachionus angulari, B. calyciflorus, Filinia novaezealandiae, Polyarthra vulgaris, Trichocerca pusilla, Rotaria neptunia, Mesocyclops kawamurai, Acanthocyclops bicuspidatus and Simocephalus vetulus were dominant species in Nansha rivers.2. During the investigation, the mean abundance of zooplankton was 138±16 ind. L-1, copepods abundance ranged from 0 to 190 ind. L-1, cladocerans ranged between 0 and 73 ind. L-1, and rotifers varied from 0 to 846 ind. L-1. A peak of abundance appeared in July and August 2015, the mean abundance(353±36 ind. L-1) was higher than that from January to April(44±7 ind. L-1). According to the results of correlation analysis between zooplankton and water quality and environmental factors, we found that the water temperature, salinity, and chlorophyll a were the main factors affecting zooplankton community structure. The rotifer abundance was positively correlated with copepod abundance and cladoceran abundance, respectively(P<0.05).3. The potential recruitment of resting eggs ranged from 14×105 to 664×105 eggs·m-3 in rivers of Nansha, and it showed the rivers next to estuary were higher than those far away from estuary. Potential recruitment of copepods resting eggs in the sediment was different with the abundance of copepod in water. There was a significantly negative correlation between potential recruitment and water temperature(P<0.01), and the potential recruitment was positively correlated with salinity and TN, separately(P<0.05). After cold storage at 4 °C for 4 weeks, 12 weeks and 24 weeks, we found that the incubation amounts of resting eggs were rising with the increase of storage time.4. The results of resting eggs hatching experiments of an aquaculture pond in Longxue Island showed that desiccation reduced the potential recruitment of resting eggs significantly(P<0.05). The resting eggs could be hatching in salinities of 0, 5, 10, 15, 20 and 25, while the highest hatching rate was observed between 10 to 20. After a storage at 4 °C for 4 weeks, we found that the potential recruitment and hatching rate of sediment resting eggs were significantly higher than those without cooling(P<0.05). And after cold storage, hatching time of resting eggs from desiccation pond was extended. These results demonstrated that the pond desiccation played important ecological roles in environmental improvement and zooplankton vertical supply of the resting eggs.5. During the investigation in July and December, 2015 on zooplankton community in ponds, reservoirs, estuaries, lakes and rivers in Guangzhou, we found that these waters were eutrophic. The species richness and abundance showed an order of Rotifer>Copepod>Cladoceran in all water bodies. Meanwhile, the species richness in summer was higher than that in winter. The seasonal trends of abundance differed among water types, i.e. the abundance in rivers, estuaries and lakes in Nansha area in summer were higher than those in winter, but the abundance of ponds, reservoirs and rivers in summer were lower than those in winter.