The Energy Basis of the Consumer Community in Streams Yesterday, Today and Tomorrow …

Abstract

Organic matter is the basic source of energy for consumers in ecosystems. In lotic ecosystems, most of the organic matter is allochthonous, imported as bank runoff or as aerial drift. Bank runoff is already processed soil material, particulate or dissolved. Unprocessed plant litter represents the aerial drift. The energy content of unprocessed organic matter is not readily available to consumers; it has to be processed by the microbial community. Microorganisms are most active in biofilms, comprised of fungi, bacteria, protozoa etc., and their organic excretions attached to surfaces. The colonizable surface area in sediments is negatively correlated with the grain size. Therefore, the largest amounts of organic matter are likely to occur in small grain size classes, which shows that biofilms are an important component of the organic matter pool. Most of the meiobenthic species, which play also a very important role in these processes, are closely connected to biofilms. These and their associated communities are doubtless an important food source for benthic consumers. The main energy pathway passes from organic matter (either particulate or dissolved) to the microbial community in biofilms, which transforms the organic matter and makes it available and palatable to benthic consumers. Wherever the benthic community is living, either in bed sediments or on macrophytic surfaces, the energy stored in biofilms or their associated communities is mostly used. IntroductionThe original aim of limnological research was to make processes predictable within water bodies. Empirical description of individual water systems should have brought limnology closer to this goal. A result of this first phase of limnological research was the realization that waterbodies are very complicated and interactive systems. Investigating the cycle of matter by tracking the relation between links, like chemical and physical variables, animals and plants, led to unforeseen difficulties. The focus on energy (i.e. viewing the energy flow through the system as interlinking parameter) facilitated this problem. The energy flow can be measured only indirectly but leads, however, to substantially clearer and simpler interpretations (BERRIE, 1976;BRETSCHKO, 1978).This keynote address for the session "The Energy Basis of the Consumer Community" (RIVER BOTTOM VI Meeting in Brno 2005) is dedicated to GERNOT BRETSCHKO, the marvellous Austrian limnologist, thinker and best friend. In the seventies, he brought the limnology of lotic ecosystems to the Biological Station Lunz (one of the cradles of limnology, founded in 1906). With his RITRODAT-LUNZ CONCEPT, he gave the Biological Station Lunz a new sense of existence. GERNOT BRETSCHKO passed by far too early in 2002, in the last phase of the 25 years research on stream ecology in the framework of RITRODAT-LUNZ. Therefore, it was not possible for him to complete the work of 25 years´ research on streams through a published compilation about RITRODAT-LUNZ. Internat. Rev. Hydrobiol. 92 2007 4-5 363-377...

Organic matter and fine grains as possible determinants of spatial and seasonal variability in bed sediment fauna: A case study from a Hercynian gravel stream

“…7). However, since biofilm is associated mainly with o100 mm grain size (Leichtfried, 2007), the possible link between fine grains and organic carbon remains unresolved by our study.…”

“…This is an important habitat for stream invertebrate fauna (Bretschko, 1981(Bretschko, , 1992, and a place of important metabolic processes (Brunke and Gonser, 1997;Claret et al, 1998;Ward et al, 1998;Leichtfried, 2007). By definition, the bed sediment is predominantly waterlogged by surface water, sharing its main physicochemical characteristics (Triska et al, 1989), and is inhabited by epigean fauna (Bretschko, 1992).…”

The Centenary of the International Review of Hydrobiology From Documentation of Single Plankton and Benthos Phenomena to Community Metabolism and Use of Molecular Probes

“…This was a very seminal issue; the latest publication of this subject in our journal was by HOFER and RICHARDSON (2007). The same was also shown by the issues "Advances in River Bottom Ecology" which were published in (e.g., WEIGLHOFER and WARINGER, 2003LEICHTFRIED, 2007;DUMNICKA et al, 2007;STAUDACHER and FÜREDER, 2007), with the late GERNOT BRETSCHKO (1938BRETSCHKO ( -2002 as the main initiator. Such papers were often driven by EU-projects for fulfilling the European Water Framework Directive (e.g., HERING et al, 2003).…”

Leaf Litter Decomposition of Three Riparian Tree Species and Associated Macroinvertebrates of Eswathu Oya, a Low Order Tropical Stream in Sri Lanka

“…Fast moving invertebrates drift from leaf to leaf searching for highly nutritious food (preferential feeding) but slow moving invertebrates, like chironomids, would stay with the remaining leaf particles (compensatory feeding). Higher nitrogen data of conditioned in comparison with unconditioned leaves confirm the development of biofilm layers, increasing the nitrogen with nearly stable carbon values, and therefore decreasing C : N ratios, indicating higher food availability for consumers (e.g., LEICHTFRIED, 2007;MARSHALL et al, 1984). Comparisons of single-species and mixed-leaf bags showed that in mixed bags there was a higher diversity of invertebrates due to the high food quality with respect to palatability for invertebrates.…”

“…Organic matter is an essential resource in most aquatic and terrestrial ecosystems (e.g., FLEITUCH and LEICHTFRIED, 2004;LEICHTFRIED, 2007;ODUM and DE LA CRUZ, 1963). Allochthonous plant litter is an important energy source for organisms in streams, especially in their upper reaches, where riparian vegetation cover limits primary production (e.g., VAN-NOTE et al, 1980;WEBSTER and MEYER, 1997).…”