The long-term patterns of phytoplankton taxonomic size-structure and their sensitivity to perturbation: A Lake Kinneret case study

Abstract

It is of great theoretical interest and applied importance to assess the structural change of the aquatic community or assemblage as a whole. Size spectrum, a tool allowing such assessment, most often describes the size distribution of organisms, irrespective of their taxonomy. The size-frequency distribution of taxonomic units in an assemblage is applied more and more often as another special case of size spectrum, and is called here traditional taxonomic size spectrum (TTSS). The Lake Kinneret (Israel) phytoplankton database was used to compare two periods of four years each, one typical and one of an extremely abnormal, perturbed community state. All eight annual TTSS curves had a similar pattern. Hierarchical cluster analysis was used to quantify the similarity between TTSS histograms. For the stable period (1982–1985), the similarity measures (Pearson r) between TTSS of any pair of years were close to the ‘ideal’ value of 1, ranging from 0.927–0.985. For the extremely abnormal period (1996–1999), they had a wider range (0.896–0.980), where the lowest estimates correspond to explicit distortions of the TTSS pattern. So the similarity comparison of TTSS histograms reveals persistent ecosystem characteristics, also giving information on strong perturbations.