[Trophic niche of medium-form and dwarf-form of purple flying squid Sthenoeuthis oualaniensis in the central and western South China Sea]. / å—æµ·ä¸­è¥¿éƒ¨æµ·åŸŸé¸¢ä¹Œè´¼ä¸­åž‹ç¾¤å’Œå¾®åž‹ç¾¤çš„è¥å »ç”Ÿæ€ä½.

To explore the characteristics of carbon and nitrogen stable isotope and trophic niche between two forms (medium-form and dwarf-form) of the purple flying squid Sthenoteuthis ouala-niensis, we collected samples from the central and western South China Sea in August 2017 to analyze the values of carbon and nitrogen stable isotope and the changes of trophic level for different mantle lengths. We further compared the trophic niche differences of the two forms populations. The results showed that for the medium-form, the δ13C value ranged from -19.54‰ to -18.10‰ and the δ15N value ranged from 7.79‰ to 9.45‰. The average trophic level of medium-form was 2.90 and ranged from 2.72 to 3.21. For the dwarf-form, the δ13C value ranged from -19.69‰ to -18.43‰, and the δ15N value ranged from 8.02‰ to 8.99‰. The average trophic level of the dwarf-form was 2.91 and ranged from 2.79 to 3.08. There were significant differences of δ15N but no differences of δ13C values between the medium-form and dwarf-form of purple flying squid. The mantle length had a significant impact on δ13C and δ15N, with the value of δ15N increasing with the mantle length. The trophic niche breadth and the trophic level of the medium-form purple flying squid were more diverse than those of dwarf-form.

[Probability distribution characteristics of stock density in offshore of northern South China Sea.] / 南海北部近海渔业资源密度概率分布特征.

Based on catch data from the bottom trawl survey by eight cruises in offshore of northern South China Sea during 2014-2017, we analyzed the stock density distribution and explored its probability distribution with statistical method, which was further used to estimate the mean stock density in this region. The results showed that the coefficient of variation (CV) for stock density ranged from 0.67 to 1.03 for all the periods, indicating a highly uneven spatial distribution of stock density. The frequency distribution of fishery resource density was characterized by obvious right-skewed, which was dominated by stock density of 0-1000 kg·km-2. The results of one sample Kolmogorov-Smirnov test indicated that three probability distribution patterns were suitable for stock density in this region, including Lognormal, Gamma and Weibull distributions. In terms of the mean stock density estimation, the values from Lognormal showed no statistically significant difference from those from others, but the opposite result was obtained between Gamma and Weibull distributions. Compared with 1960s-1970s, the appropriate probability distribution pattern of stock density has changed from single to multiple types. Variation of the proportion of low catch resulted from the changes in the structure of fishery resources, fishing effort and climate change might cause the alte-ration of probability distribution.

Planktonic community structure during a harmful bloom of Phaeocystis globosa in a subtropical bay, with special reference to the ciliate assemblages.

Planktonic community structure was investigated during outbreak of harmful Phaeocystis globosa bloom in a subtropical bay, the Maowei Sea, South China Sea. The phytoplankton assemblage was numerically dominated by colonial P. globosa, with its abundance ranging from 1.23 × 10(8) to 11.12 × 10(8) cells m(-3) and contributing nearly 90 % to the total abundance. Totally 66 mesozooplankton (>169 µm) and 19 ciliates species were recorded, with the densities ranged from 169 to 1633 ind m(-3) and 74 to 1118 cells L(-1), respectively. The dominant species for mesozooplankton were Copepoda (larvae), Bestiola sinicus, B. amoyensis, Macrura (larvae) and Acartia spinicauda, respectively. The ciliate assemblage was numerically dominated by Codonella rapa, Strombidium globosaneum and Mesodinium rubrum. During the bloom, P. globosa seemed to be negatively affected by the nutrient phosphate significantly (p < 0.05). However, no correlation between P. globosa and ciliate assemblage was detected, but P. globosa was negatively correlated with total biomass of mesozooplankton and abundance of B. sinicus (p < 0.05), suggesting that P. globosa was uncoupled from the grazing by both ciliates and mesozooplankton when appearing as colonies form. On the other hand, both positive and negative correlations among the dominant groups of mesozooplankton and ciliates were observed (p < 0.05) which possibly indicated that the predation of mesozooplankton upon ciliates might be strengthened during the Phaeocystis bloom and the complex effect also varied from species to species.

[Pollution by heavy metals in the petrochemical sewage waters of the sea area of Daya Bay and assessment on potential ecological risks].

This study aimed to gain a clear understanding on the status of pollution by heavy metals in the petrochemical sewage and the potential ecological risk caused by heavy metal pollution in the sea area of Daya Bay. The contents and spatial distributions of heavy metals including Zn, Pb, Cu, Cd, Cr, As and Hg in seawater, sediment and fishes collected from Daya Bay were analyzed. The comprehensive pollution index (CPI) and ecological risk indexes (ERIs) were used to evaluate the contaminated severity and potential ecological risks of heavy metals in seawater and sediment. The results showed that the contents of these heavy metals, except for those of Zn and Pb, in several stations set in Daya Bay from 2011 to 2012 were relatively low, which were lower than the quality standard of class I according to the China National Standard Criteria for Seawater Quality, suggesting that the seawater in Daya Bay has not been polluted yet by these heavy metals. The average CPI of heavy metals in seawater during flooding season (0.72) was higher than that during dry season (0.38) whereas the average CPI of heavy metals in sediment during dry season (7.77) was higher than that during flooding season (5.70). Hg was found to be the primary contaminating heavy metal in sediment during dry season, which was followed by As and Zn whereas during flooding season, Hg was the primary contaminating metal in sediment, followed by Zn and Cu. The contents of these 7 heavy metals in fishes collected from the surveyed areas were lower than those of the standard requirements. A correlation analysis indicated that there were significant differences in the correlations between the midst of the heavy metals in sea water and the different periods. The ERIs of heavy metals in sediment during dry season (129.20) was higher than that during flooding season (102.86), and 25% of the sampling sites among all stations were under the risk of high-level alarm. The potential ERIs of heavy metals in sediment in offshore waters were higher than those of inshore waters, and were higher in the bay-mouth than in the bay-head. However, the distributions of potential ERIs showed reversed trend during dry season. The comprehensive assessment results showed that Hg was the primary heavy metal with a high ecological risk whereas the potential ERIs for the other six heavy metals in the petrochemical sewage waters in Daya Bay were relatively low.

[Risk assessment of coastal ecosystem in Beibu Gulf, Guangxi of South China].

Based on the marine ecological investigation in the coastal area of Beibu Gulf, Guangxi in September 2009, a GIS-based evaluation was conducted on the present status of ecological environment quality, including seawater quality, nutrient level, biomass, primary productivity, biodiversity, and ecological buffer capacity, in the area in autumn, and the integrated ecological risk index (ERI) was adopted to assess the risk of the coastal ecosystem in the Gulf. In September 2009, the study area had a better ecological environment quality. Most of the risk indicators were at medium or lower level, and the total area was overall at low ecological risk level. The ERI showed that there was an obvious spatial heterogeneity in the distribution of the ecological risk. The nearer to the harbors, the higher the risk was.