Towards a quality assessment of freshwater ecosystems through the morphological analysis of phytoplankton.

Among the organisms living at low Reynolds numbers, those belonging to the ecological group of phytoplankton offer an amazing morphological diversity and all the scientists involved in phytoplankton research have commonly observed that they may express a quite high variability, both intra- and inter-specific, in their size and morphology. These features have been traditionally used just for taxonomic classification. However, the ecological value of morphological descriptors in phytoplankton is increasingly used to investigate their abilities in resource (light and nutrients) uptake as a result of natural selection and competition. At the same time, the analysis of suitable morphology and size descriptors can offer a useful tool to assess the ecological status of inland waters. In this presentation the relevance of phytoplankton size and morphology in depicting the ecological status of water bodies is shown by considering i) the role of their size in nutrient uptake and ii) the role of their morphology in light harvesting. The way in which the morphology of phytoplankton organisms cope with the hydrodynamic condition of a given water body is also shown. In addition, an account on the main research trends about the role of morphology in the definition of morpho-functional traits of phytoplankton is offered. Morpho-functional classification of freshwater phytoplankton can be viewed as complementary of taxonomy and is a promising tool to better understand the functioning of aquatic ecosystems. Investigating the variability of phytoplankton size and morphology and integrating these features in a coherent frame may offer a vast array of new perspectives in the field of phytoplankton ecology and aquatic research as well as a simplified, low-cost tool to perform water quality monitoring.