Diagnostic model construction and example analysis of habitat degradation in enclosed bay: II. spatiotemporal variations in habitat degradation in Sansha Bay

The process of habitat degradation varies in habitat type and driving force which shows certain spatial and temporal heterogeneity on regional scales. In the present study, a new diagnostic model for enclosed bay habitat degradation was established, with which the spatial and temporal variation patterns of habitat degradation during 1991–2012 in Sansha Bay, Fujian, China was investigated. The results show that anthropogenic disturbance is the major controlling factor for the habitat degradation in large temporal heterogeneity in the bay. On the other hand, the habitat degradation experienced signifi cant spatial variations among six sub-bays. Under the joint action of temporal and spatial heterogeneity, the degradation trend in growing scale shows a more signifi cant correlation with the distribution of local leading industries along shorelines. Therefore, we quantifi ed the main characters of habitat degradation in Sansha Bay, and have understood the relationship between the status of habitats spatio-temporal variation value and the main controlling factor leading to the changes. However, a defi ciency of this research is the lack of or inaccessible to the detailed data, which shall be better solved in the future study for accessing more data from more sources.

Diagnostic model construction and example analysis of habitat degradation in enclosed bay: I. diagnostic model construction

Presently, research is lacking regarding the diagnosis and evaluation of habitat degradation in enclosed bay systems. We established a diagnostic model for enclosed bay habitat degradation(EBHD model) using a multi-approach integrated diagnostic method in consideration of driving force-pressurestate-infl uence-response. The model optimizes the indicator standardization with annual average change rate of habitat degradation as the basic element, to refl ect accurately the impact of the change and speed of degradation on the diagnostic results, to quantify reasonably the contribution of individual diagnostic indicator to habitat degradation, and to solve the issue regarding the infl uence of subjective factors on the evaluation results during indicator scoring. We then applied the EBHD model for the Sansha Bay in Fujian Province, China, evaluated comprehensively the situation of habitat degradation in the bay, and screened out the major controlling factors in the study area. Results show that the diagnostic results are consistent in overall with the real situation of the study area. Therefore, the EBHD model is advantageous in terms of objectivity and accuracy, making a breakthrough in diagnosis and evaluation for habitat degradation in enclosed bay systems.

Homogeneous selection is not always important in bacterial community in the eutrophic enclosed bay

Background:Previous studies have found that coastal eutrophication increases the influence of homogeneous selection on bacterial community assembly.However,whether seasonal changes affect the dominance of homogenous selection in bacterial community assembly in eutrophic bays remains unclear.Sansha Bay is an enclosed bay with ongoing eutrophication,located in the southeast coast of China.We investigated the bacterial community composition at two depths of the enclosed bay across seasons and the seasonal variation in community assembly processes.Results:Diversity analyses revealed that the bacterial community composition among seasons differed significantly.By contrast,there was little difference in the community composition between the two depths.The temperature was the key environmental factor influencing the community composition.The null model indicated that the relative importance of homogeneous selection decreased in the following order:spring>winter>autumn>summer.Homogeneous selection did not always dominate the community assembly among seasons in the eutrophic bay.The effects of pure spatial variables on the community assembly were prominent in autumn and winter.Conclusions:Our results showed the seasonal influence of eutrophication on bacterial community diversity.The seasonal variation in composition and structure of bacterial communities eclipsed the vertical variability.Eutrophication could enhance the importance of homogeneous selection in the assembly processes,but the seasonal environmental differences interfered with the steady-state maintained by ongoing eutrophication and changed the community assembly processes.Homogeneous selection was not always important in bacterial community in the eutrophic enclosed bay.The bacterial community was the most complex in summer,because the composition differed from other seasons,and the assembly process was the most intricate.These findings have contributed to understanding bacterial community composition and assembly processes in eutrophic coastal ecosystems.