The Study Of Jiaozhou Bay Ecosystem Dynamic Change

The paper is focused on Jiaozhou Bay, one of our country typical gulfs. Based onthe long-term field observation and history data, the long-range changes of JiaozhouBay ecosystem were studied. The main result is as follows:The air temperature in the area of Jiaozhou Bay showed a trend of increasingwith fluctuation during the past100years. The increase in temperature was the mostsignificant in the winter and least in the summer. It was also found that there weresignificant correlation relationship between the variation of annual mean temperatureand PDO (Pacific Decadal Oscillation) index. The changing trend of the watertemperature was in consistent with the air temperature, especially in winter. Thesalinity showed a trend of decreasing since1981, especially in the summer. Thevariation rate of the surface salinity was-0.064/yr for the annual mean, and-0.131/yrin August. The changing trend of salinity was contrary to the adjacent sea area, suchas the Bohai Sea and some area of the Yellow Sea.2. Results indicated that the concentrations of all of the five kind of nutrientsshowed a trend of increasing during the last several decades. The concentration ofammonium increased gradually from1980s, reaching a peak in2001and decreasedsince then. The increasing trend of the concentration of nitrite and nitrate wassignificant from1990s, especially after2000. The concentration of phosphate andsilicate was increased mainly after1998. Although the imbalance state of the nutrientwas alleviated comparing to the1990s, it is still necessary to control the increase ofDIN. It is also important to pay attention to the dramatic increase of nitrate andphosphate concentration due to the excessive use of the fertilizer. 3. Results indicated that there was no significant change on the spatialdistribution pattern of chlorophyll a concentration during the last20years. Theconcentration of Chl a showed a decreasing trend from the north-eastern andnorth-western part to the center area, the southern part, the mouth and the outer areaof the bay. The change on the seasonal characteristics of Chl a concentration wasevident. The Chl a concentration increased in the winter and summer, but decreased inthe spring and autumn. In the long term frame, the Chl a concentration was fluctuated,ranging from1to4.76mg m-3. The long term changes of the Chl a concentration andprimary productivity were affected by the increase of nutrient concentration and thefiltering pressure of maricultured shellfish in Jiaozhou Bay.4. Results indicated that the micro-and nano-phytoplankton was the maincomposition of the phytoplankton in the surface water in Jiaozhou Bay. Thenano-phytoplankton was dominant in the bottom layer, and the percentage was higherthan90%. The seasonal change of the size composition in the surface water wassignificant, with the micro-phytoplankton dominating in the winter and autumn andthe nano-phytoplankton dominating in the spring and summer. No apparent seasonalchange was observed on the size composition in the bottom layer, and thenano-phytoplankton was the dominant component at all seasons. During the past20years, the percentage of micro-plankton increased gradually, which was thought to beaffected by the long term change of nutrient concentration and structure.5.The total abundance of phytoplankton was increasing in the Jiaozhou Bay since1981, and the increase was evident since2000, especially in the winter. No clearchanges presented in the distributional pattern of total abandance of phytoplankton.As for dominant phytoplankton species, they changed in recent years, e.g. thedominant specis included all along Skeletonema costatum, Chaetoceros Curvisetus,Coscinodiscus asteromphalus, Chaetoceros debilis, Pseudonitzschia pungens,Eucampia zoodiacus et al. in the recent fifty years, while some pytoplankton specieswhich was ever dominated before1990's, including Guinardia striata, Rhizosoleniaalata f. Indica, Hemiaulus sinensis et al., was not dominant any more since2000.Furtermore, the new dominant species (e.g. Chaetoceros lorenzianus, Chaetoceros densus, Lithodesmium undulatus, Ceratium furca, Ceratium fusus et al.) wereappeared in the recent five years. The variation of community structure ofphytoplankton in Jiaozhou Bay was related to the increase of temperature, the clearlyincreasing concentration of total inorganic nitrogen and changes of proportion ofnutrient composition in the winter and spring.6.The biomass of zooplankton was pronouncedly increasing in recent years in theJiaozhou Bay. The average biomass was up to0.361g/m3from2001to2008, equaledto3.54times biomass of them in1990's. The abundance of zooplankton wasincreasing before2000, then it was fluctuant after2000, which was related tovariation of zooplankton species compostion. The seasonal variation pattern ofbiomass and abundance of zooplankton indicated that they were highest in summer in1990's while they were highest in spring, secondly in summer since2000. Results ofstudies about the long changes of key functional groups of zooplankton showed thatthe abundance of medusae and salps was increasing, especially the medusae in therecent20years. The variation of abundance of copepods and chaetognaths presentedfluctuant on this condition.