Characterization Of Marine Bacterial Diversity And Their Seasonal Variations In Xiangshan Bay Shellfish Culture Areas

Xiangshan bay is semiclosed near ningbo east coast.In recent years, with the rapid development of port industry,agriculture and aquaculture, Xiangshan bay environment is deteriorating.The aquaculture industry have a negative impact.In this paper,the experiment area is set up in cage culture area of Xiangshan bay. Select two locations for shellfish aquaculture, oysters and clam were stocked. With culturing, the seawater and sediment are collected from breeding areas at 5 time points from August 2009 to August 2010. Through the sample, investigate bacterial diversity and community structure to understand the culture zone microbial community structure in xiangshan Bay. Study the environment situation of the culture process through bacteriological and provide data for future bioremediation and environmental monitoring.The number of bacteria is detected by traditional culture methods. Bacterial species include heterotrophic bacteria,nitrifying bacteria,sulfuring bacteria,vibrio,nitrate-reducing bacteria and sulfate-reducing bacteria. The changes of heterotrophic bacteria in the oyster and clam breeding area are small and the water and sediment heterotrophic bacteria in the number of changes have significant correlation. From the time distribution, the heterotrophic bacteria and temperature have obvious correlation. The nitrifying bacteria and sulfuring bacteria in all oyster and hairy clam breeding area are detected, but the number is not great, with the shellfish farming to continue to have some fluctuations. The change of quantity of this two bacteria can response environment changes. The result shows shellfish culture zones is less affected by land. In process of breeding, the number of vibrios has a wide fluctuation. In November 2010 there have been massive reproduction of Vibrio in seawater,but in sediment it does not change significantly. Hence, need for aquaculture water bodies to make some adjustments, so as not to cause disease outbreaks because of Vibrio overgrowth. In hairy clam breeding area the high nitrate-reducing bacteria in sediment is detected,shows that the sediment has high levels of nitrate. The sulfate-reducing bacteria in the hairy clam culture area have great number in beginning, but as the culturing it reduces to minimal content in the final development.Using PCR- denaturing gradient gel electrophoresis (DGGE) technique makes a preliminary analysis to Xiangshan shellfish bacterial diversity in sediment samples and their changes with time. Oyster culture areas have a higher bacterial diversity index values, the diversity index over time do not change significantly. From the view of similarity index there are the larger similarity of the adjacent time, but between March 2010 and May 2010, the similarity index value is small.The reason may be artificially breeding operation on the environmental impact of farming from small to big, so that the bacterial communities in the results are significant changes. To August 2010, populations of bacteria in the environment have becoming larger trend, but the dominant population has not changed significantly. Bacteria diversity index in clam culture zone is slightly lower than the oyster culture area. The change rate is relatively small. Degree of similarity, hairy clam breeding areas in different periods is lower similarity to the bacterial diversity, which to some extent, reflect the environmental changes Clam culture zones more intense than oyster culture areas, deep degree of change. In this region , to August 2010 bacterial diversity also has a trend of increased. The number and the location of bands from DGGE profiles show on the breeding areas during this period that the large population of bacteria appear which the front period does not.Synthesizing the results of culture and PCR-DGGE method can draw a conclusion. In the process of these shellfish growing, the change of the environment is more gentle, no significant deterioration occurred. To some extent, growth of shellfish can co-ordinate the interaction between different environment factors, making the breeding microenvironment is more stable. Until the late breeding period, several types of cultured bacteria multiply. The result is in accord with what was detected by PCR-DGGE. It indicate that the breeding environment may have occured changes and should be made preparations to prevent environmental degradation.