Plankton Ecology

  • Controlling factors (biological, environmental, genetic)
  • Inter- and intraspecific variability
  • Responses of target organisms (evolutionary, behavioural)
  • Effects on population dynamics: Inter-algal and grazer interactions
  • Effects on planktonic food webs

Chemical interactions between species have been widely studied in terrestrial ecology but are less well known in marine ecosystems, especially among planktonic protists. In the marine plankton, temporal and spatial changes of biomass and species composition have traditionally been thought to be mainly regulated by resource availability and abiotic factors. However, there is increasing evidence that interspecific interactions in the plankton play a major role in succession, food web structure and bloom development. Many HAB species are regarded as rather poor exploitation competitors in terms of growth rate and/or resource uptake capabilities. There is some evidence for the hypothesis that a number of HAB species may gain dominance by the production of bioactive compounds, particularly secondary metabolites that affect growth or elicit other physiological responses in other organisms. Such allelochemicals may be targeted to exclude competitors from exploiting limited resources (interference competition), as well as to avoid/reduce predation.

By combining microscopy, protistan culture experiments and field surveys the following topics are worked on:

  • Taxonomy, morphology, phylogeny, and behaviour of toxic protists
  • Development and application of protist-interaction-based bioassays for identification of bioactive compounds
  • Effects of chemical interactions on planktonic food webs

Dr. Urban Tillmann

Bioactive compounds of toxic marine  protist  might be involved in competitiona and grazing interaction and/or might  play a role in communication or may have other yet undetermined function.

Feeding interaction among plantonic dinoflagellates. The mixotrophic species Fragilidium subglobosum attacks and engulfs the larger spiny species Ceratium tripos

Killing grazers and/or competitors by lytic compounds will favour bloom formation of harmful species