Phytoplankton/Phytobenthos

Co-ordinator / Fachgruppenleiter: Dr. Katrin Teubner

Overview

The aim of the phytoplankton/phytobenthos expert group is to stimulate studies, monitoring activities and discussion forum on algae across the Danube River countries, for researchers and other people who are interested to advance our knowledge on this second large river ecosystem in Europe.

The role of photosynthetic microorganisms for ecosystem health of Danube River

The expert group on phytoplankton and phytobenthos focuses on the community structure and function of photosynthetic microorganisms in the Danube River. These organisms are floating in the water column or live attached to a surface substrate of the riverbed. Many species of them are eukaryotic algae; some are prokaryotic photosynthetic bacteria. Their function in the Danube River ecosystem is manifold. These microbial primary producers synthesise organic compounds by utilising inorganic nutrients and solar energy and are hence the autotrophic base for the food webs in River Danube. They serve as food for many consumers from heterotrophic unicellular microorganisms to fish. As the species composition of phytoplankton and phytobenthos varies among stretches from the source to mouth of the Danube River, in response the community structure of consumers also changes. Microbial primary producers are organisms of particular short generation time, of about up to one cell division per day in natural habitats. Environmental changes within hours to days as fluctuations among the three main nutrient elements (phosphorus, nitrogen and silica), underwater light availability, chemical interaction with macrophytes, pH and concentrations of trace metals and other toxic compounds, grazing pressure; and also alterations of physical conditions as of water velocity and water temperature, are therefore, often responded promptly by photosynthetic microbes. This immediate response can be measured by physiological alterations as e.g. by photosynthesis, respiration or growth, pigment pattern or cellular content of organic compounds. Finally, many environmental changes may also lead to changes of microbial population densities shifting species composition within phytobenthos and phytoplankton assemblages. The both aspects of autotrophic microbes, their base role for food chains and their sensitivity to habitat changes, stimulated transboundary research activities on phytoplankton and phytobenthos for a better understanding of the Danube River ecosystem (see ICPDR reports by Joint Danube Surveys, supported by the Danube countries). Studies on community structure, biodiversity and growth of autotrophic microbes are central to indicate the ecosystem health of River Danube from the source to mouth.

Presentations about phytoplankton and phytobenthos during IAD-conferences

In the history of IAD-conferences, beginning in the 1950s, studies on algae and other photosynthetic microbes have a long tradition. During recent IAD-conferences, about 12-15% of the presentations of Danube research relate to phytoplankton or phytobenthos studies. They describe in detail the frequency distribution of rare and common microbial autotrophs across the Danube River and its tributaries, their response to environmental forces linked to other organisms within benthic and planktonic community and their use as bioindicators for microhabitat reference conditions. In recent years the wider implication of the response of microbial primary producers to pollution&eutrophication and global climate change has been communicated. Both issues are addressed by current research initiatives of the European community, the ‘European Water Framework Directive’ and European framework programs on Climate response of Ecosystems in Europe.