| The macrobenthos and some environmental factors collected from 40 stations in the Changjiang estuary and adjacent waters were investigated in February, May, August and November, 2007. The species numbers, biomass, density, diversity, secondary production of macrobenthos in the regain were studied and analyzed. In addition, the relationship between the distribution of macrobenthos and environmental factors was also analyzed. The major results of the study are presented as follows: 1. From the material collected from 40 stations in the Changjiang Estuary in February, May, August and November, 2007, 216 macrobenthos species were found, in which 113 species were polychaetes, making up 52.31% of the total species, 42 species were mollusks, making up 19.91%, 32 species were crustaceans, making up 14.35%, 10 species were echinoderms, making up 4.63%, and 19 species were other groups of marine animals, making up 8.80%. The total mean biomass and density were estimated to be 8.76 g/m2 and 139.18 ind/m2, respectively. The average specie number, biomass and density in spring were respectively 86, 6.96 g/m2 and 143.18 ind/m2;100, 4.71 g/m2 and 157.06 ind/m2 in summer; 113, 20.25 g/m2 and 185.00 ind/m2 in autumn; 62, 3.11 g/m2 and 71.47 ind/m2 in winter. Data showed that distribution of species numbers, biomass and density in the estuary increased from Changjiang mouth to easten outside open sea. The biomass and density of macrobenthos were significantly positive correlated with depth and salinity. They had significantly negative correlation with the COD, TN, TP and TSM. Compared with history data in the same region, the species numbers, biomass and density were all lower than twenty years ago. 2. The richness index (D), species evenes index (J) and Shannon-Wiener index (H'), were used to study the diversity of macrobenthos in the Changjiang Estuary. The results showed the following: The average values of D of four cruises were 1.23 in spring, 1.10 in summer, 1.41 in autumn, 0.85 in winter; J of four cruise were 0.92 in spring, 0.89 in summer, 0.90 in autumn, 0.94 in winter; H'of four cruise were 2.06 in spring, 1.72 in summer, 2.06 in autumn, 1.74 in winter. J and H'were significantly positive correlated with depth and salinity. They had significantly negative correlation with the COD, TN, TP and TSM. J had no significantly correlation with any environmental factors.3. Based on the data obtained from 40 stations in 2007, the secondary production and P/B ratio in the Changjiang Estuary was calculated with Brey's empirical formula. The results showed as the following: The distribution of secondary production in the estuary increased from Changjiang mouth to easten outside open sea. The mean value of secondry production in the studied area was 1.36 g(AFDW)/ (m2·a), in which 0.63 g(AFDW)/ (m2·a) was polychaetes, making up 46.32% of the total value, 0.26 g(AFDW)/ (m2·a) was mollusks, making up 19.12%, 0.25 g(AFDW)/ (m2·a) was crustaceans, making up 18.38%, 0.12 g(AFDW)/ (m2·a) was echinoderms, making up 8.82%, and 0.10 g(AFDW)/ (m2·a) was other marine animals, making up 7.35%. The mean P/B ratio of macrobenthos was 0.89, in which 1.75 was polychaetes, 0.76 was mollusks, 0.42 was crustaceans and 0.86 was echinoderms.4. Comprehensive investigation on macorbenthos and environmental factors in the Changjiang Estuary and adjacent waters were conducted in 2007. Canonial correspondence analysis (CCA) was applied to explore the relationship between macrobenthos and environmental factors using CANOCO. The results showed that the macrobenthos communities can be classified into three assemblages. The ordination of interrelation among the three assemblages and their correlation to the environmental variables were revealed by CCA; the result shows that salinity, depth, nutrient and total suspended particulate matter were major factors influencing the macorbenthors assemblage.The polychaete, Neanthes japonica, is a worm-like euryhaline species native to China and Japan. In China, this species inhabits the intertidal, shallow sandy-mud sediments and/or estuaries in the Bohai Sea and the Yellow Sea. Recently in China, N. japonica has been widely used as an ideal diet in shrimp aquaculture and as fishing bait, and marked with high commercial value. The aim of this study was to examine the effect of temperature and salinity on the metabolism, energy budget and nitrogen budget of N. japonica. The results of this study provide useful information for aquaculturists engaged in the artificial breeding of N. japonica. The major results of the study are presented as follows:1. In this study, the relations of body weight, salinity (5, 10, 15, 20, 25, 30 and 35) and temperature (18, 21, 24, 27 and 30 oC) to oxygen consumption and ammonia excretion of N. japonica were determined by bioeologics method. Three different groups in body weight (Large: 2.34±0.36 g, Middle: 1.50±0.21 g and Small: 0.62±0.12 g) were set for all experiments. The results were as follows: the rates of oxygen consumption and ammonia excretion of N. japonica were affected by body weight, salinity and temperature (P<0.05). The body weight was negatively related to the rates of oxygen consumption and ammonia excretion. Significant relationship between oxygen consumption rate/ammonia excretion rate and body weight was obtained. With salinity changed from 5 to 35, the rates of oxygen consumption and ammonia excretion decreased before 30 and then increased, indicating that both lower and higher salinity were adverse and certain salinity stress was necessary for enhancing the energy demand. Raising temperature from 18 to 30 oC, the oxygen consumption rate increased before 27 oC and then decreased. However, the relation of ammonia excretion and temperature seemed more complex. Moreover, significant effects (P<0.05) were obtained on salinity/temperature and body weight on oxygen consumption and ammonia excretion. The O:N (oxygen/nitrogen) ratio varied greatly in this case from 5.97 to 463.22, indicating that N. japonica can regulate the type of metabolic substrate against environment changes. 2. The growth and energy budget of polychaete, N. japonica at five salinity levels (15, 20, 25, 30 and 35 ppt) with a total sample of four replicates for each level, were investigated in this study. Results indicate that the growth, as indicated by final dry weight and specific growth rate (SGR), significantly increased with increasing salinity, with the maximum level at 30 ppt salinity, and then decreased at the highest salinity level. A similar tendency was observed in food consumption, food conversion efficiency (FCE) and apparent digestive rate (ADR). For the pattern of energy allocation, faeces energy was only a small component of the energy budget, and did not have the capability to greatly influence the proportion of energy intake allocated to growth. The respiration metabolism significantly increased as salinity decreased and accounted for a large portion of energy intake for each salinity treatment. The nitrogen excretion was acute with changing salinity. Therefore, respiration energy and excretion energy of the energy budget were the major factors influencing the proportion of energy intake allocated to growth. These results revealed that salinity mainly affected the polychaete's growth by influencing food consumption, FCE, ADR, or energy allocation to growth. In addition, regression equations described and obtained the relationship among food consumption, faecal production, SGR, ADR, FCE, proportion of energy intake allocated to growth (G/C), respiration (R/C), excretion energy (U/C), faeces (F/C) and salinity. As calculated from these regression equations, the optimal salinity range for the growth of N. japonica may be between 27 and 30 ppt. The average energy budget of N. japonica under five salinity treatments was: 100C = 25.37G + 8.50F + 4.92U + 61.21R, where C was food energy, G was growth energy, F was faeces energy, U was excretion energy and R was respiration energy.3. Growth and energy budget of the polychaete, Neanthes japonica, at various temperatures (17, 20, 23, 26 and 29 oC) were investigated in this study. The growth, as indicated by final dry weight and specific growth rate (SGR), increased with increasing temperature, with the maximum level at 26 oC, and then decreased significantly at 29 oC. A similar trend was observed in feeding rate, food conversion efficiency (FCE) and apparent digestive rate (ADR). However, no significant differences were detected in ADR among all the temperature treatments. For the pattern of energy allocation, faeces energy was only a small component of energy budget and had little influence on the proportion of food energy allocated to growth. The metabolic energy accounted for a large portion of energy intake for each temperature treatment. The nitrogen excretion was acute with changing temperature. The two expenditure terms (respiration energy and excretion energy) of energy budget were the major factors influencing the proportion of food energy allocated to growth. These results revealed that temperature affected the growth of N. japonica mainly by influencing feeding rate and FCE. In addition, regression equations described the relationship between feeding rate, faecal production, SGR, FCE and temperature were obtained. Optimum temperature for feeding rate, FCE and SGR were estimated at 25.01 oC, 24.24 oC and 24.73 oC, respectively, from the regression equations.4. In the present study, the effect of salinity on nitrogen growth and nitrogen budget of N. japonica was investigated at 15, 20, 25, 30 and 35 by bioeologics method. The result showed that nitrogen consumption, nitrogen growth, nitrogen faeces, nitrogen food conversion efficiency and specific growth rate were significantly affected by salinity. They all increased with increasing salinity, peaked at about 30, and then decreased with increasing salinity. Reversed tendency was observed in nitrogen excretion. There was no significant differences in nitrogen apparent digestive rate among all salinity treatments. As calculated from regression equations, the optimal salinity range for nitrogen growth of N. japonica might be 28~29. The results indicated that the high nitrogen growth of the polychaete at suitable salinity mainly resulted from the significant increase of nitrogen consumption and nitrogen food conversion efficiency at corresponding salinity. All part of nitrogen budget were significantly affected by salinity. The minimum of proportion of nitrogen excretion was at salinity 25, above or below the salinity, the value decreased, which was reversed with the proportion of nitrogen growth and faeces. The proportion of nitrogen excretion was the major factor influencing the nitrogen budget model. The average nitrogen budget of N. japonica under five salinity treatments was: 100CN=49.01GN+42.45UN+8.54FN, where CN was nitrogen consumption, GN was nitrogen growth, UN was nitrogen excretion and FN was nitrogen faeces. In addition, primary discussion on the nitrogen budget of aquatic animals was made.5. The effect of temperature on nitrogen growth and nitrogen budget of Neanthes japonica was investigated at 17, 20, 23, 26 and 29 oC by bioeologics method. The results showed that nitrogen consumption, nitrogen growth, nitrogen food conversion efficiency and specific growth rate were significantly affected by temperature. They all increased with increasing temperature, peaked at about 26 oC, and then decreased with increasing temperature. There was no significant differences in nitrogen absorption efficiency among all temperature treatments. As calculated from regression equations, the optimal temperature range for nitrogen growth of N. japonica might be 23~26 oC. The results indicated that the high nitrogen growth of the polychaete at suitable temperature mainly resulted from the significant increase of nitrogen consumption and nitrogen food conversion efficiency at corresponding temperature. All parts of nitrogen budget were significantly affected by temperature. The minimum of proportion of nitrogen excretion was at 26 oC, above or below the temperature, the value decreased, which was reversed with the proportion of nitrogen growth and faeces. The proportion of nitrogen excretion and nitrogen growth were the major factors influencing the nitrogen budget model. The average nitrogen budget of N. japonica under five temperature treatments was: 100CN=49.2GN+42.3UN+7.5FN.
|
PDF Full Text Request