Control of biofilm-dwelling ciliate communities by temperature and resources

Laboratory and field-related experimental approaches were combined to investigate the impacts of temperature and resource enhancements on the development of biofilm-dwelling ciliate communities. The first part of this study concentrated on ciliate community responses towards experimental warming. It was shown that temperature increase during winter can significantly accelerate the early colonization of biofilms by ciliates and enhance the organism density when the resource supply is sufficient. This can also result in the formation of significantly altered ciliate communities in consequence to temperature increases. In contrast, temperature increase during summer reduces the carrying capacity of biofilms for ciliates when the resource density is low. This finding was confirmed by the results of an experiment with cross-manipulations (temperature- and resource enhancements), in which the negative effect of warming was buffered by supplemental resources The second part of this work concentrated on the responses of biofilm-dwelling ciliate communities towards resource enhancements from two different origins, namely benthic and planktonic bacteria. It was shown that ciliate community responses towards benthic bacteria enrichments are often limited, whereas the ciliates can generally profit from planktonic bacteria enhancements. Such stimulation could either occur directly by the enhancement of suspension-feeding ciliates at especially high temperatures, whereas indirect ciliate community responses were detected, especially at low temperatures. Here, their enhancement was coupled to a previous enhancement of suspension-feeding heterotrophic flagellates, which in return were grazed upon by ciliates. The magnitude of responses strongly depended on the seasonal conditions with regards to both the environmental setting as well as to the presence or absence of ciliate consumers (micrometazoa). The latter finding was also confirmed for pre-grown, mature ciliate communities. Taken together, the different aspects of this study demonstrated that when considered separately, both factors (i.e. temperature and resource density) can significantly affect the development and the structure of biofilm-dwelling ciliate communities. However, the magnitude of community responses towards manipulations of either factor was tightly coupled to the environmental conditions with particular regards to the ambient resource load (in the experiments with temperature enhancements) and to the ambient water temperature (in the experiments with resource enhancements). This demonstrates that temperature and resource availability interactively control the development and the structure of biofilm-dwelling ciliate field communities. Admittedly, ciliate community responses to environmental changes can be hidden due to grazer activities. Although, the assumption of community responses towards environmental changes always has to consider the environmental background (temperature, resource availability, grazer activity) besides of shifts in particular variables

Resource quantity and seasonal background alter warming effects on communities of biofilm ciliates

The impacts of experimental warming on field-related communities of biofilm ciliates were studied in contrasting seasons (winter vs. summer), which incorporated both different species sets and environmental background conditions. The biofilms for the experiments were cultivated in river bypass systems that were exposed to increasing temperatures based on the ambient river temperature. Opposing effects of warming were observed for ciliate 'summer' and 'winter' communities. While winter warming resulted in both stimulation (abundance and biomass) of the ciliate communities and significant shifts in the community structure, summer warming induced a significant decline in the ciliate biomass, but did not affect the relative community composition. By the simultaneous manipulation of temperature and resource density in summer, it was demonstrated that negative warming effects on the ciliate quantity during summer could be compensated by increasing the availability of food. Taken together, our results indicate that the responses of ciliate communities towards warming are strongly coupled to the availability of resources, and that the strongest impacts of environmental warming should thus be expected in resource-rich environments

Disturbance alters the response of consumer communities towards warming: a mesocosm study with biofilm-dwelling ciliates

Environmental warming can have negative effects on the carrying capacity of communities because metabolic rates increase at the expense of biomass. Here, we tested the hypothesis that such warming effects are reversed in communities experiencing disturbance, as temperature-driven growth processes gain relevance and can compensate for negative disturbance effects. Model communities of semi-natural, biofilm-dwelling ciliates were cultivated in mesocosms (river bypass systems) under two temperature regimes (ambient temperature and increased by 4 degrees C). The interactive effects between these different temperatures and seven disturbance intensities were tested in a nested design. Disturbance generally reduced total ciliate abundances, whereas only small effects on the prevalence of functional diversity were detected. Temperature effects differed between different disturbance intensities and seasons: Whereas warming reduced the carrying capacity of undisturbed communities irrespective of the season, pronounced positive warming effects were detected under disturbance in winter and, to a lesser extent, in spring. Neither significant temperature nor disturbance effects were recorded in summer, probably because ciliate growth rates were not temperature limited due to high summer background temperatures. Our results show that disturbance can markedly alter warming effects on temperature limited communities. Since natural communities commonly face disturbance, it should therefore be considered in models of future environmental warming responses

Anthropogenic Stressors Shape Genetic Structure: Insights from a Model Freshwater Population along a Land Use Gradient

Environmental pollution including mutagens from wastewater effluents and discontinuity by man-made barriers are considered typical anthropogenic pressures on microevolutionary processes that are responsible for the loss of biodiversity in aquatic ecosystems. Here, we tested for the effects of wastewater treatment plants (WWTPs), weirs and other stressors on the invertebrate species <i>Gammarus pulex</i> at the population genetic level combining evolutionary ecotoxicology, body burden analysis and testing for exposure to mutagens. Exposure to chemical pollution alone and in combination with the presence of weirs resulted in a depression of allelic richness in native <i>G. pulex</i> populations. Our results suggest that the input of a mutagenic effluent from a WWTP resulted in a strong increase in private alleles over the affected populations. In addition, the presence of weirs along the river disrupted the migration across the river and thus the gene flow between <i>G. pulex</i> upstream and downstream. This study provides strong evidence that the assessment of genetic variation including private alleles together with the contamination of mutagenic and nonmutagenic chemical pollution offers new insights into the regulation of genetic population structure and highlights the relevance of emerging anthropogenic pressures at the genetic level

Tandem Action of Natural and Chemical Stressors in Stream Ecosystems: Insights from a Population Genetic Perspective

Agricultural and urban land use has dramatically increased over the last century and one consequence is the release of anthropogenic chemicals into aquatic ecosystems. One of the rarely studied consequences is the effect of land use change on internal concentrations of organic micropollutants (OMPs) in aquatic invertebrates and its effects on their genotype diversity. Here, we applied population genetic and internal concentrations of OMPs analyses to determine evolutionary implications of chemical pollution on <i>Gammarus pulex</i> populations from a natural and two agricultural streams. Along 14 consecutive months sampled, 26 different OMPs were quantified in <i>G. pulex</i> extracts with the highest number, concentration, and toxic pressure in the anthropogenically stressed stream ecosystems. Our results indicate distinct internal OMP profiles and changes in both genetic variation and genetic structure in streams affected by anthropogenic activity. Genetic variation was attributed to chemical pollution whereas changes in the genetic structure were attributed to environmental disturbances, such as changes in discharge in the impacted stream ecosystems, which worked both independently and in tandem. Finally, we conclude that human-impacted streams are subjected to severe alterations in their population genetic patterns compared to nonimpacted stream ecosystems

The food web perspective on aquatic biofilms

Biofilms, the complex communities of microbiota that live in association with aquatic interfaces, are considered to be hotspots of microbial life in many aquatic ecosystems. Although the importance of attached algae and bacteria is widely recognized, the role of the highly abundant biofilm-dwelling micrograzers (i.e., heterotrophic protists and small metazoans) is poorly understood. Studies often highlight the resistance of bacterial biofilms to grazing within the microbial food web and therefore argue that the micrograzers have a modulating role (i.e., have effects on biofilm phenotype) rather than a direct trophic role within biofilms. In the present review, we show that this view comes too short, and we establish a conceptual framework of biofilm food webs consisting of three major elements. (1) Energy pathways and subsidization from plankton. As inhabitants of interfaces, biofilm-dwelling grazers potentially access both planktonic organisms and surface-associated organisms. They can play an important role in importing planktonic production into the biofilm food web and thus in the coupling of the planktonic and benthic food webs. Nevertheless, specialized grazers are also able to utilize significant amounts of autochthonous biofilm production. (2) Horizontal complexity of the basal food web. While bacteria and algae within biofilms are edible in general, food quality and accessibility of both bacteria and algae can differ considerably between different prey phenotypes occurring during biofilm formation with respect to morphology, chemical defense, and nutrient stoichiometry. Instead of considering bacteria and algae within biofilms to be generally resistant to feeding by micrograzers, we suggest considering a horizontal food-quality axis to be at the base of biofilm food webs. This food quality gradient is probably associated with increasing costs for the micrograzers. (3) Vertical food web complexity and food chain length. In addition to the consumption of bacteria and algae, many predatory micrograzers exist within biofilm food webs. With the help of video microscopy, we were able to demonstrate the existence of a complex food web with several trophic levels within biofilms. Our conceptual framework should assist in integrating food web concepts and processes into whole-biofilm budgets and in understanding food-web-related interactions within biofilms

Microbes in aquatic biofilms under the effect of changing climate

The effects of climate change on aquatic biofilm structure and function is difficult to predict mainly due to biofilms being complex and dynamic assemblages of microorganisms. We review observed patterns of the effects of warming and desiccation on biofilms. Commonly observed effects of warming on biofilms include changes in the autotrophic community composition and extracellular polymeric substances, stimulation of the heterotrophic community, and changes in the microbes, protozoa and small metazoans densities and composition. The magnitude of the temperature effects depends on the biofilm successional stage, resources availability, community composition and interactions within communities including top-down effects. Temperature also affects biofilm functioning by direct control of biological activities and by selecting adapted taxa, which provide feedback on activities. Biofilm photosynthesis, respiration, denitrification and extracellular enzyme activities show differential sensitivity to temperature. Results suggest a significant effect of temperature on the nitrogen cycling and a link between the specific community composition and the biofilm temperature sensitivity. On the other hand, desiccation may produce more permanent changes on the biofilm microbial community composition than on extracellular enzyme activities, the effects also depending on species specific sensitivity and biofilm structure (such as the content of extracellular polymeric substances). At the ecosystem level, both factors (warming and desiccation) may coincide in time, but few studies have looked at the drought?temperature interactions on aquatic biofilms. Future trends might include multistress and short- and long-term experimental approaches. Measurements of carbon and nitrogen budgets are needed to quantify the effects of biofilm metabolism on ecosystem nutrient cycling and, at the same time, to improve biofilm modelsFil: Romaní, Anna M.. Universidad de Girona; EspañaFil: Boulêtreau, Stéphanie. Université Paul Sabatier; FranciaFil: Diaz Villanueva, Veronica. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; ArgentinaFil: Garabetian, Frédéric. Universite de Bordeaux; FranciaFil: Marxsen, Jürgen. Justus Liebig University; AlemaniaFil: Norf, Helge. Helmholtz Centre for Environmental Research; AlemaniaFil: Pohlon, Elisabeth. Justus Liebig University; AlemaniaFil: Weitere, Markus. Helmholtz Centre for Environmental Research; Alemani