The Clearance Rate And Carrying Capacity Of Transplant Enhanced Manila Clam (Ruditapes Philippinarum) In Jiaozhou Bay

The manila clam Ruditapes philippinarum was one of the important marine biological resource species in our country. It ever distributed widely in Jiaozhou Bay and had a long fishing history of more than 70 years. Because of the increasing demand of the domestic and international market to the clams, the fisherman enlarged the fishing efforts after 1980's, which caused the serious decline of natural resources. Presently the clams are mainly farmed in Jiaozhou Bay and the main farming areas are located in the north coast of Jiaozhou Bay. The enhanced clam seedlings were mainly immigrated from Putian city, Fujian province after 2000. The relation between physiology of the clams and environmental factors has not yet been reported.The effects of environmental factors including water temperature, salinity and pH on the clearence rate (CR) of the enhanced manila clams were studied in the laboratory. The data was compared with that of the local population to study the adaptability of the immigrant population.The algal bloom took place frequently in Jiaozhou Bay in recent years, which made the pH of the seawater instable, so the effects of pH on the CR of the enhanced manila clams were studied in this paper. The carrying capacity of manila clams in Jiaozhou Bay was roughly estimated by the method of energy balance. The main results are summarized as follows.1. Effect of water temperature on the CR of transplant enhanced manila clamsAt the six temperatures of the experimental range 8-33℃, the CR increased firstly, reached the peak at temperature 23℃and then decreased with the increase of the temperature. The CR increased rapidly from temperature 13℃to 18℃and changed smoothly at others. One-factor analysis of variance showed that there was a highly significant differences in CR at different temperatures (P<0.01); The changing tendency of CR at age 2 was significantly positively correlated with that of age 3 (r=0.9569,P<0.01) at different temperatures.There was a very similar effect of the tempreture on the CR of both the enhanced manila clams and the natural ones.2. Effect of water salinity on the CR of enhanced manila clamsThe transplanted manila clams were able to adapt themselves to the obvious changes in salinity. The CR increased with salinity ranging from 15 to 30, the maximum value appeared at salinity 30, then it decreased at salinity 35. One-factor analysis of variance showed that the CR at salinity 15 was significantly lower than those at the other salinities (P<0.05) and there was no significant differences from 20 to 35. The changing tendency of CR at age 2 was significantly positively correlated with that of age 3 (r=0.9895, P<0.01)at different salinities.3. Effect of water pH on the CR of transplanted manila clamsAt the five pH values from 6.2 to 10.2, the CR increased firstly and then decreased with the increase of the water pH , and the maximum value appeared at pH 8.2 . One-factor analysis of variance indicated that the CR is significantly different at different pH (P<0.01). The changing tendency of CR at age 2 was significantly positively correlated with that of age 3 (r=0.9876, P<0.01)at different pH. The most suitable pH for transplanted manila clams was about 8.2, and the activity of the clams would be restrained when pH was at about 6.2 or more than 9.2.4. It is reasonable to estimate the carrying capacity of the manila clams in June because that the rate of net flesh is relatively higher, and the manila clams keep a higher grazing pressure on the phytoplankton and the stock of POC. The best carrying capacity for age 2 was 237.9 thousand ton and 327.1 thousand ton for age 3, respectively.5. According to the annual tracing investigation on the mortality, the suitable breeding density of the manila clams was estimated, 565(ind/m2)and 743(ind/m2)for age 2 and age 3 respectively. While the actual cutivated density was 2500(ind/m2), which was significantly beyond the end of proper density, and that's reason why the young clams kept a relatively higher mortality.From the results mentioned above, it is showed that the transplant enhanced manila clams adapted to the change of the temperature and the salinity. The output has already overpassed the suitable capacity due to the sustain ably increased cultivation.The present state and the sustainable development of cultivated manila clam industry in the Jiaozhou Bay were also analyzed. Finally some suggestions were put forward to provide the certain technique supports and decision basis for maintaining the healthly development of clam industry.