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)(1983)(1984)(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)(1997)(1998)(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.

Lago Maggiore oligotrophication as seen from the long-term evolution of its phytoplankton taxonomic size structure

“…Like the NBS, the species size-distribution patterns observed for pelagic and benthic assemblages seem to be rather stable even during pronounced changes in community composition (Havlicek & Carpenter 2001;Kamenir et al 2006). At the same time, changes of the TTSS fine structure are often evident.…”

“…Water for chemical analyses was collected monthly and nutrient concentrations were determined at the chemical laboratory of the Istituto per lo Studio degli Ecosistemi (Pallanza), following the methods reported in Mosello & Ruggiu (1985). These procedures of data sampling and processing were very similar to protocols followed up at Lake Kinneret [described in detail in Zohary (2004)], where TTSS long-term consistency was originally found (Kamenir et al 2006).…”

“…The 'ataxonomic' biomass size spectrum (BSS) and normalized biomass size spectrum (NBS) are closely connected to a more traditional one, where the size-frequency distribution of species or higher taxa is plotted (Hemmingsen 1934;Hutchinson & MacArthur 1959;Smith et al 2004). While, in some important cases, not all registered taxonomic units are determined and described at the species level, we apply the operational taxonomic unit (OTU) approach (Sneath & Sokal 1973), and refer to such size distribution of taxonomic units as traditional taxonomic size spectrum (TTSS; Kamenir et al 2006).…”

“…At the same time, changes of the TTSS fine structure are often evident. Therefore, comparisons of statistical distributions of species can produce quantitative similarity or distance measures estimating the change in the community composition between two points in time (Thibault et al 2004;Kamenir et al 2006). Consequently, TTSS, a simple and flexible presentation of an important property of the community (i.e., its taxonomic composition), seems to be a promising tool needed for ecological monitoring, forecasts, and quantitative assessments of the aquatic assemblage structural deformations.…”

“…Consequently, TTSS, a simple and flexible presentation of an important property of the community (i.e., its taxonomic composition), seems to be a promising tool needed for ecological monitoring, forecasts, and quantitative assessments of the aquatic assemblage structural deformations. The interesting and valuable phenomenon (for many theoretical and applied applications) of long-term consistency of the general pattern of phytoplankton TTSS was initially established for one lake (Kinneret; Kamenir et al 2006). The following studies (Kamenir et al 2008) have supported its more general nature, including oligotrophic lake condi-tions.…”