Abstract:Marine bacteria in water or sediment are often closely linked to environmental conditions in their surrounding, thus influencing their distribution and abundance. In order to estimate the distribution of marine bacteria in Xiangshan Bay, undisturbed overlying seawater, sediment and surface seawater bacteria were analysed by staining with 4, 6-Diamidino-2-Phenylindole and observed with Epifluorescence Microscope (EFM). Environmental parameters such as seawater temperature (ST), salinity (SS), pH, dissolved oxygen (DO), chemical oxygen demand (COD) as well as NO-3-N, NO-2-N, DIN, NH+4-N, DIP, TN, PO3-4-P and chlorophyll a (Chla) values were measured at the same time. Samples were collected with a cylindrical high fidelity gravity sampler instead of the conventional grab sampler.
Bacteria abundance in July 2007, October 2007, January 2008 and April 2008, representing the situation for summer, autumn, winter and spring, ranged from 1.50×105 to 9.78×1010 cells/mL (cells/g), with a mean of 2.76×109cells/mL (cells/g). Significantly high values could be observed for bacteria abundance in July (summer) compared to other sampling time. A red tide outbreak during the sampling event in April 2008 could have contributed to the lowest bacteria abundance value observed for the whole study period. In vertical direction, the number of bacteria in the overlying water or in the sediment was higher than that in the surface seawater. The mean number of bacteria abundance in overlying water, in the sediment and in surface seawater was 9.70×107cells/mL, 7.40×109 cells/mL and 4.61×109cells/mL respectively. In horizontal direction, we draw the contour maps of the number of bacteria with the software 'surfer 8.0’. According to the contour map we found that the number of bacteria decreased from the top to the mouth of the bay with higher abundance near the breeding areas. Very high values of bacteria abundance was also observed near power plant: sample from station S25 showed higher bacteria abundance than other stations during all the cruises. Seawater temperature, the nutrients (NO-3-N, DIN), pH, Chla and COD of the surface seawater were significantly positive (P < 0.01) correlated with the bacteria abundance of the surface seawater while DO and the nutrients (NH+4-N) of the surface seawater were significant negative correlated (P < 0.01) with the bacteria abundance of the surface seawater. Bacteria abundance of overlying seawater were significant positive correlated (P < 0.01) to seawater temperature, the nutrients (NO-2-N, DIP) and the pH of bottom seawater whereas DO was significant negative correlated (P < 0.01). The results of multivariate statistical analysis showed that dissolved oxygen, seawater temperature, the nutrients (N, P), pH and organic pollution were the main factors influencing the abundance and distribution of marine bacteria in Xiangshan Bay.
Such spatial distribution of bacteria demonstrated that anthropogenic coastal land pollution from industrial and agricultural activities and from maricultures played the key roles in the occurrence of marine benthic bacteria.