Ciliates as engineers of phototrophic biofilms |
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Authors: | ELLEN J WEERMAN HARM G
Van Der GEEST MYRA D
Van Der MEULEN ERIK M M MANDERS JOHAN
Van De KOPPEL PETER M J HERMAN WIM ADMIRAAL |
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Institution: | 1. Centre for Estuarine and Marine Ecology, Netherlands Institute of Ecology (NIOO‐KNAW), Yerseke, The Netherlands;2. Aquatic Ecology and Ecotoxicology, Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam, Amsterdam, The Netherlands;3. Centre for Advanced Microscopy, Swammerdam Institute, University of Amsterdam, Amsterdam, The Netherlands |
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Abstract: | 1. Phototrophic biofilms consist of a matrix of phototrophs, non‐photosynthetic bacteria and extracellular polymeric substances (EPS) which is spatially structured. Despite widespread exploitation of algae and bacteria within phototrophic biofilms, for example by protozoans, the ‘engineering’ effects of these ciliates on the spatial heterogeneity of phototrophic biofilms are poorly studied. 2. We studied the potential engineering effects of two ciliates, Urostyla sp. and Paramecium bursaria, on the spatial heterogeneity of synthetic multispecies biofilms. Biomass of phototrophic organisms, EPS and bacteria was analysed three dimensionally using confocal laser scanning microscopy. Spatial heterogeneity and cover of the phototrophs, bacteria and EPS were determined at several depths within the biofilm. 3. Ciliate species did not interfere with the overall development of phototrophic microorganisms, because the thickness of the biofilm was equal whether the ciliates were present or not, even though their abundance did affect spatial heterogeneity of biofilm components. When Urostyla was present, it reduced aggregation in EPS and bacteria and increased EPS biovolume. This implies a local facilitating effect of ciliates on photosynthetic activity. Biofilms to which Paramecium was added did not differ from controls in terms of phototrophs, EPS cover and biovolume. Nevertheless, ciliates affected the spatial heterogeneity of these components as phototrophs and EPS became more evenly distributed. 4. This study shows that ecosystem engineering by organisms does not only occur at large spatial scales, as in grasslands and estuaries, but also plays a role at the microscopic scale of biofilms. This effect on spatial heterogeneity was not driven by substantial exploitation of biofilm components, but via the subtle engineering effects of ciliates. |
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Keywords: | Paramecium bursaria protozoan grazing spatial variance three‐dimensional structure Urostyla sp |
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