Structure and functioning of lacustrine food webs

Contact: Marina Manca (Unit of Verbania)
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Lake Orta

The term “trophic status” is widely used to describe both the abundance of nutrients and the intensity of biological productivity supported by the nutrients flux. Lake Maggiore and other lakes (e.g. Orta and Candia) have been monitored for chemical, physical and biological parameters for many years. Lake Maggiore, originally oligotrophic and phosphorus-limited, underwent a period of moderate eutrophication between 1960 and 1980, due to an increase of soluble reactive phosphorus.

Lake Candia

The ensuing oligotrophic phase did not reverse the eutrophication process entirely. Long-term data indicate that not only bottom-up (phosphorus loading), but also top-down control by zooplankton grazing (which in turn is controlled by fish) may have been effective.  Interaction among organisms, the study of processes and the mechanisms related to the dynamics of natural populations, as well as the prediction of trophic response and associated water quality, are the main goals of this research group.

Research

Figure 1(A) Figure 1(B)

Our research focus is biodiversity in lakes and rivers, and the changes occurring with different types of anthropogenic and biological stressors, including trophic changes, pollution, infrastructures, global warming and invasions by alien species. We are at present investigating, in particular, which traits may be related to functional diversity, to define both ecological indicators and the trophic roles of different taxa of plankton, benthos and fish fauna. This approach will allow us, among other things, to predict the degree of functional resilience which is associated in a given system to changes in taxa composition. An example of the changes in the functional traits of planktonic assemblages in Lake Maggiore occurring with changes in trophic status is given in Figure 1A and Figure 1B

FieldWork

The research outlined below is designed to analyze functional diversity and the response mechanisms (physiological adaptation/clonal selection) of organisms to different stressors:

  1. Multidisciplinary studies (chemical, hydromorphological and biological) on lakes and rivers to highlight the processes controlling the structure and function of ecosystems, and the interactions between biotic and abiotic factors.
  2. Changes in size and shape of phytoplanktonic cells, to predict which species might become dominant under certain environmental conditions.
  3. Development of biological quality indices based on biotic communities (phytoplankton, benthos, fish, macrophytes), according to the European Water Framework Directive (2000), also taking into account the chemical contamination of lake-waters and the occurrence of invasive alien species.
  4. C and N stable isotopes signatures of zooplankton taxa, to identify throughout the season:
    - food sources and the contribution of littoral carbon to secondary production;
    - the trophic position of different taxa and their overlapping, to estimate the level of redundancy and the transfer of energy and matter to the planktivores.
  5. Re-visiting long-term contemporary data (>20 years) to identifying:
    - taxonomic and functional diversity changes;
    - population phenology and the production of resting stages;
    - bottom up/top down mechanisms with changes due to anthropogenic pressure.
  6. Comparison between contemporary/past response of organisms to pollutants, by using resting eggs as a source for life table experiments.
  7. Investigating the relationship between environmental changes and blooms of toxic cyanobacteria.
  8. Use of indicator organisms to evaluate the accumulation of algal toxins and their propagation along the trophic web.
  9. Evaluation of the dynamics of invasions by alien mollusc species and of their impact on the ecosystem.
  10. Taxonomy, biology and biogeography of macroinvertebrates, in particular Diptera Chironomids.
  11. Studies on remote alpine lakes and streams, as a tool for assessing the reliability, resilience and conservation of freshwater ecosystems.
  12. Spread and impact of alien fish species on lake ecosystem functioning.
  13. Abundance and distribution of aquatic macrophytes
  14. Speciation, macroecology and patterns of diversity, mostly using as a test case microscopic invertebrates such as rotifers.