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A modified type of species size-frequency distribution or "taxonomic size spectrum" (TSS) was applied to analyze phytoplankton structural change under environmental impacts, using Lake Kinneret as a monitoring database. While the ‘traditional’ TSS (TTSS) describes the distribution of the operational taxonomic unit (OTU) number into size classes, the frequency-weighted TSS (FTSS) distributes the frequency of occurrence of OTUs in water samples, accounting for the water mass occupancy by algal species, i.e., the time-spatial structure of the studied assemblage. FTSS consistency was proven for two dramatically different monitoring periods, where the "extreme" period (1996-1999) was characterized by pronounced deformations of the established patterns of phytoplankton annual succession for the "stable" period (1982-1985). Quantitative similarity estimates for the phytoplankton assemblage taxonomic time-spatial structure were produced by cluster analysis. Specific changes in the FTSS fine structure were evident and helpful for diagnostics, being more pronounced during the extreme years. The descriptors providing quantitative similarity comparisons for the aquatic assemblage structure, while not requiring deep taxonomic knowledge, may be helpful for lake managers and environmental agencies. |
