東京湾における力イアシ類群集の長期変化と現状

摘要

Using monthly time series data for zooplankton in Tokyo Bay, Japan, I investigated seasonal changes in the existing copepod community, and documented the phenological and quantitative changes in the populations of three dominant species (Acartia omorii, Centropages abdominalis, and Labidocera rotunda), which undergo diapause by laying resting eggs in response to climatic and hydrographic variations in this semi-enclosed eutrophic coastal area. Using cluster analysis, three seasonal community groups were detected, and seasonal shifts in structure of communities were explained in light of the life history characteristics of indicator species and seasonal changes in the hydrographic environment. Decreasing abundance and increasing resting egg periods were observed for two cold-water species (A. omorii and C. abdominalis), and the reverse for warm-species (L. rotunda) during 30 years. Time series analysis revealed a possible mechanism driving these phenological shifts. Wintertime warming of the water column associated with climatic variability driven by the Pacific Decadal Oscillation index, followed by rapid development of summertime stratification and the formation of hypoxic bottom water layers, were responsible for the early initiation and delayed termination of the resting egg period in cold-water species. These results suggest that multiple stressors such as climate change and other anthropogenic impacts can affect regional zooplankton communities in coastal areas.