A multitude of studies underline the pivotal role of parasites for ecological processes supporting the theory that parasite diversity is closely linked to ecosystem functions and integrity. However, it has been poorly studied how parasite diversity is directly or indirectly altered by the increase and release of multiple stressors and how this translates into overall community composition and ecological functioning. Therefore, we will study the effects of stream degradation and restoration on parasite communities and subsequent effects on free-living organisms.

We expect that stressors predominantly affect parasites with complex life cycles, i.e. specialists and heteroxenous parasites, while parasites with simple life cycles (generalists and monoxenous parasites) may increase in abundance. We further expect generalists to colonise restored stream sections first and that communities of free-living species greatly impact the colonization success of parasites. Finally, as parasites will also affect stressor susceptibility of their hosts, we hypothesise that parasitised individuals show a parasite-modulated drift and dispersal behaviour.

To test the above listed hypotheses, samples of macroinvertebrates (snails and arthropods) for the analysis of parasite communities will be obtained from non-degraded, degraded and restored sites (A17, Z02). In cooperation with A11, parasites will be determined in fish (sculpins) and infection data will be correlated to the overall genetic diversity and immune competence of the fish. In cooperation with A12 and A13, we will determine if the trophic position of parasites in a food web will change during phases of stream degradation and recovery. Joint experiments with A08 in the ExStream system will allow for comparing the response of parasitised and unparasitised hosts to experimentally induced stressors. In collaboration with project A16, we will analyse parasitism as a factor driving host dispersal processes. A09 will thus link various experimental and field projects by analysing the response of metazoan parasite communities as well as the role of metazoan parasites as modulators of free-living species’ dispersal during degradation and recovery processes.

Sebastian Prati (University of Duisburg-Essen)

Effects of stream degradation and recovery on metazoan parasite communities: a multiple stressor approach

Many studies underline the pivotal role of parasites in ecological processes, supporting the theory that parasite diversity is closely linked to ecosystem functions and integrity. However, it has been poorly studied how parasite diversity is directly or indirectly altered by increasing and releasing multiple stressors and how this translates into overall community composition and ecological functioning.

The aim of this project is to investigate the effects of stream degradation and restoration on metazoan parasite communities and subsequent effects on free-living organisms. Therefore, fish, snails, and benthic invertebrates will be sampled from 40 field sites of the Emscher/Boye and Kinzig catchments in non-degraded, degraded, and restored sites and screened for parasites. Additionally, samples of macroinvertebrates collected from near-natural and restored sites in the Boye system over the last ten years will be analyzed. Parasitological data will be compared between sites to provide insights into the overall community structure and potential temporal trends. The responses of parasitized and unparasitized macroinvertebrate hosts will be experimentally induced using the ExStream system.

Contact: sebastian.prati@uni-due.de

First Supervisor: Prof. Dr. Bernd Sures (Universtiy of Duisburg-Essen, Aquatic Ecology)
Second Supervisor: PD. Dr. Christian K. Feld (Universtiy of Duisburg-Essen, Aquatic Ecology)
Mentor: Dr. Sebastian Emde (Landesamt für Natur, Umwelt und Verbraucherschutz Nordrhein-Westfalen (LANUV))