Strategie del fitoplancton e modificazioni nella struttura delle comunità: un caso di studio

Abstract

Phytoplankton community composition generally undergoes to temporal changes which may be regarded as modifications in the strategies adopted by the different populations. Actually, phytoplankton species have developed distinct adaptive strategies, which involve modifications of cell morphology and physiology that allow them to thrive in pelagic environments which are inherently very unstable. Since changes of community composition are really population replacements and these partly depend upon population strategies, it can be helpful to consider community changes in terms of population strategies. Therefore, the aim of this paper is to study changes in phytoplankton community of a reservoir, on different time scale (weekly, monthly), taking in account the population strategies involved. The phytoplankton of hypertrophic Arancio reservoir was analyzed during one year (1990–91). It has been adopted the common classification of strategies in a r–K continuum that represents concepts widely recognized in phytoplankton ecology. In particular, population strategies have been ascertained using features such as time span of occurrence, average growth and loss rates and algal biovolume. Algal groups comprising phytoplankton community were envisaged using multivariate classification analyses. Statistical correlations between phytoplankton biomass of different strategic groups recognized and environmental factors (e.g. euphotic depth, mixing depth, nutrients concentration, temperature) were calculated. Considering that nothing in the correlation definition implies that the relation between both variables must be casual, nevertheless the results suggest that factors which control the main phytoplankton community changes, at least at the time scales adopted, are pertained to the physical environment.

Key Words:

• phytoplankton
• short-
• long-term dynamics
• population strategies