ABSTRACT: During the year 2002, the size variability of most of the species found in Lago Maggiore was analysed in detail, measuring
through image analysis the main morphological parameters (maximum linear dimension, surface, volume) of the algal cells. Many
individuals belonging to the same species were measured sampling by sampling, collecting about 28,000 data.
This data set allowed us to evaluate the morphological plasticity of many species across the seasonal succession: through
multivariate statistical analysis we compared the changes of cell volume, cell surface, maximum linear dimension and surface-to-volume
ratio to the fluctuations of the main physical and chemical parameters.
The responses we observed were variable, depending on the different taxonomic groups or species as well as on the morphometric
parameter considered. As a general pattern, a strong seasonality of the size changes was observed, mainly dependent on the
gradients of nutrients and temperature.
Hydrobiologia 04/2012; 578(1):47-57. · 1.78 Impact Factor
ABSTRACT: In 1996, we studied the phytoplankton seasonal succession in Lago Maggiore (N. Italy) through weekly sampling. Such a frequency enabled us to evaluate the changes of the phytoplankton assemblage in the light of the equilibrium and non-equilibrium theories. The distinct phases of changing of the species composition were identified separating the samples by means of cluster analysis and non-metric multidimensional scaling (NMDS). We recognised well distinct phytoplankton associations, whose seasonal succession followed a clear cyclic path throughout the year, with spring and summer phases respectively characterised by a rapid turn-over of the assemblages and by a relative stability. Moreover, we observed an increase of species number and Shannon-Wiener diversity during the spring, followed by a summer decline of the diversity in spite of an unchanged species number. Because of the dominance of the same few species for about two months during summer, coupled with small fluctuations of the total biomass, we could identify the summer assemblage as a steady state assemblage. The aim of the present contribution, although describing the whole seasonal succession, is to draw the attention towards the species composition at the steady state, taking into account the functional properties of the species involved. The possible role of the metalimnetic niche in selecting a particular summer assemblage in deep and large lakes will be discussed.
Hydrobiologia 06/2003; 502(1):37-48. · 1.78 Impact Factor
ABSTRACT: The main goal of the study presented here is to identify a repeatable pattern in the seasonal succession of phytoplankton assem-blages in Lago Maggiore. In order to fulfil this objective we analysed the phytoplaktonic succession during a five years period (1995-1999), through the calculation of the Bray-Curtis similarity index applied to biovolume data. A cluster analysis has been then applied to the distance matrix, allowing the identification of sample clusters possessing a similar species composition. The comparison, through the whole period considered, of the phytoplankton assemblages characterising each cluster allowed to recog-nise six seasonal periods (Winter, Early Spring, Late Spring, Early Summer, Late Summer, Autumn), each of them characterised by a peculiar and repeatable species assemblage. Among the most interesting findings we would mention the existence of a Late Spring/Early Summer association, dominated by Planktothrix rubescens and Fragilaria crotonensis, probably peculiar of the deep subalpine lakes, where these species can better take advantage of the physical and chemical environment of the metalimnetic niche. The identification of a pool of dominant and sub-dominant species common to other southern subalpine lakes and the existence of a similar time periodicity in the development and decline of most of them across this lake district seem to be promising in order to give our results a wider application.
J. Limnol. 01/2002; 61:129-145.