[Invertebrate assemblage structure associated with key environmental factors in the Yangtze River Estuary, China.] / é•¿æ±Ÿå£æ— è„Šæ¤ŽåŠ¨ç‰©ç¾¤èšç‰¹å¾åŠå ¶ä¸ŽçŽ¯å¢ƒå› å­çš„å ³ç³».

Yangtze River Estuary plays a key role in linking the river and ocean ecosystems. Our understanding on its biodiversity and associated ecological processes remains poor, which is especially true for the invertebrate assemblage. Here, we investigated invertebrate assemblage pattern and associated environmental drivers based on four different seasonal comprehensive investigations across this region in 2014. A total of 35 species, belonging to 20 families, 10 orders and three phylums were identified. Crustaceans (19 species) and mollusks (13 species) were the taxa with higher richness. Dominant invertebrate included Palaemon gravieri, Crangon affinis, Ovalipes punctatus, Acetes chinensis, Portunus trituberculatus and Charybdis bimaculata. Total density and biomass was 4518.96 kN·km-2 and 173.09 kg·km-2 respectively, with the highest value in spring and the lowest in autumn. Biodiversity indices peaked in winter and spring and reached the lowest in summer. Invertebrate assemblage structure showed significant seasonal variation, appearing in a significant difference between the near-shore and the off-shore in spring, and between the northern-waters and southern-waters in other seasons. Results from ordination analysis showed that the spatial variation of invertebrate was mainly regulated by temperature and dissolved oxygen, whereas Chla and nutrient factors played key roles in driving the temporal community assemblage in this region.

[Distribution and source of particulate organic carbon and particulate nitrogen in the Yangtze River Estuary in summer 2012].

Based on the data from the cruise carried out in August 2012 in the Yangtze River Estuary and its adjacent waters, spatial distributions of particulate organic carbon (POC), particulate nitrogen (PN) and their relationships with environmental factors were studied, and the source of POC and the contribution of phytoplankton to POC were analyzed combined with n (C)/n (N) ratio and chlorophyll a (Chl a) in the Yangtze River Estuary in summer 2012. The results showed that the concentrations of POC in the Yangtze River Estuary ranged from 0.68 mg x L(-1) to 34.80 mg x L(-1) in summer and the average content was 3.74 mg x L(-1), and PN contents varied between 0.03 mg x L(-1) and 9.13 mg x L(-1) with an average value of 0.57 mg x L(-1). Both of them presented that the concentrations in bottom layers were higher than those in the surface. POC and PN as well as total suspended matter (TSM) showed a extremel similar horizontal distribution trend that the highest values appeared in the near of the mouth and southwest of the survey waters, and decreased rapidly as toward the open seas, both of them showed higher contents in coastal zones and lower in outer sea. There was a fairly good positive linear relationship between POC and PN, which indicated that they had the same source. POC and PN expressed significantly positive correlations with TSM and chemical oxygen demand (COD), but showed relatively weak correlations with salinit and chlorophyll a, which demonstrated that terrestrial inputs had a strong influence on the distribution of POC and PN, and phytoplankton production was not the major source of organic matters in the Yangtze River Estuary. Both the n (C)/n (N) ratio and POC/Chl a analysis showed that the main source of POC was terrestrial inputs, and organic debris was the main existence form of POC. Quantitative analysis showed the biomass of phytoplankton only made an average of 2.54% contribution to POC in the Yangtze Rive Estuary in summer and non-living POC occupied the overwhelming advantage.

[Characteristics of ichthyoplankton assemblages in Yangtze Estuary and adjacent waters in spring].

Based on the investigation data of ichthyoplankton assemblages and environmental factors in Yangtze Estuary and adjacent waters in May 1999 and 2001, the characteristics of ichthyoplankton assemblages in these areas in spring were studied by using TWINSPAN (two-way indicator species analysis) and CCA (canonical correspondence analysis). A total of 11 540 ichthyoplankton individuals were taxonomically identified, belonging to 11 orders, 18 families and 32 species, of which, Coilia mystus, Engraulis japonicus, Chaeturichthys hexanema, Allanetta bleekeri, and Trachidermis fasciatus were the dominant species. The ichthyoplankton communities were classified into three assemblages by using TWINSPAN, i.e., estuarine assemblage dominated by C. mystus, coastal assemblage dominated by A. bleekeri and T. fasciatus; and shelf assemblage featured by E. japonicus and C. hexanema. The CCA ordination of the interrelations among the three assemblages and their correlations to the environmental variables revealed that salinity, depth, dissolved oxygen, and total suspended particulate matter were the major factors affecting the ichthyoplankton assemblages in the study areas.