@article{WeithoffMoserKamjunkeetal.2010,
  author    = {Weithoff, Guntram and Moser, Michael and Kamjunke, Norbert and Gaedke, Ursula and Weisse, Thomas},
  title     = {Lake morphometry and wind exposure may shape the plankton community structure in acidic mining lakes},
  issn      = {0075-9511},
  doi       = {10.1016/j.limno.2009.11.002},
  year      = {2010},
  abstract  = {Acidic mining lakes (pH <3) are specific habitats exhibiting particular chemical and biological characteristics. The species richness is low and mixotrophy and omnivory are common features of the plankton food web in such lakes. The plankton community structure of mining lakes of different morphometry and mixing type but similar chemical characteristics (Lake 130, Germany and Lake Langau, Austria) was investigated. The focus was laid on the species composition, the trophic relationship between the phago-mixotrophic flagellate Ochromonas sp. and bacteria and the formation of a deep chlorophyll maximum along a vertical pH-gradient. The shallow wind-exposed Lake 130 exhibited a higher species richness than Lake Langau. This increase in species richness was made up mainly by mero-planktic species, suggesting a strong benthic/littoral - pelagic coupling. Based on the field data from both lakes, a nonlinear, negative relation between bacteria and Ochromonas biomass was found, suggesting that at an Ochromonas biomass below 50 mu g CL-1. the grazing pressure on bacteria is low and with increasing Ochromonas biomass bacteria decline. Furthermore, in Lake Langau, a prominent deep chlorophyll maximum was found with chlorophyll concentrations ca. 50 times higher than in the epilimnion which was build up by the euglenophyte Lepocinclis sp. We conclude that lake morphometry, and specific abiotic characteristics such as mixing behaviour influence the community structure in these mining lakes.},
  language  = {en}
}
@article{TittelBissingerZippeletal.2003,
  author    = {Tittel, J{\"o}rg and Bissinger, Vera and Zippel, Barbara and Gaedke, Ursula and Bell, Elanor M. and Lorke, Andreas and Kamjunke, Norbert},
  title     = {Mixotrophs combine resource use to outcompete specialists: Implications for aquatic food webs},
  year      = {2003},
  abstract  = {The majority of species can be grouped into those relying solely on photosynthesis (phototrophy) or those relying solely on the assimilation of organic substances (heterotrophy) to meet their requirements for energy and carbon. However, a special life history trait exists in which organisms combine both phototrophy and heterotrophy. Such 'mixotrophy' is a widespread phenomenon in aquatic habitats and is observed in many protozoan and metazoan organisms. The strategy requires investment in both photosynthetic and heterotrophic cellular apparatus, but the benefits must outweigh these costs. In accordance with the mechanistic resource competition theory, laboratory experiments revealed that pigmented mixotrophs combined light and prey as substitutable resources. Thereby, they reduced prey abundance below the critical food concentration of competing specialist grazers [Rothhaupt, K. O. (1996) Ecology 77, 716-724]. Here, we demonstrate for the first time the important consequences of this strategy for an aquatic community. In the illuminated surface strata of a lake, mixotrophs reduced prey abundance so steeply that grazers from higher trophic levels, consuming both the mixotrophs and their prey, could not persist. Thus, the mixotrophs escaped from both competition and grazing, and remained dominant. Furthermore, the mixotrophs structured the prey abundance along the vertical light gradient creating low densities near the surface and a pronounced maximum of their algal prey at depth. Such deep algal accumulations are typical features of nutrient poor aquatic habitats, previously explained by resource availability. We hypothesize instead that the mixotrophic grazing strategy is responsible for deep algal accumulations in many aquatic environments.},
  language  = {en}
}
@article{TittelBissingerGaedkeetal.2005,
  author    = {Tittel, J{\"o}rg and Bissinger, Vera and Gaedke, Ursula and Kamjunke, Norbert},
  title     = {Inorganic carbon limitation and mixotrophic growth in Chlamydomonas from an acidic mining lake},
  issn      = {1434-4610},
  year      = {2005},
  abstract  = {Plankton communities in acidic mining lakes (pH 2.5-3.3) are species-poor because they face extreme environmental conditions, e.g. 150 mg l(-1) Fe2++Fe3+. We investigated the growth characteristics of the dominant pigmented species, the flagellate Chlamydomonas acidophila, in semi-continuous culture experiments under in situ conditions. The following hypotheses were tested: (1) Low inorganic carbon (IC) concentrations in the epilimnion (e.g. 0.3 mg l(-1)) arising from the low pH limit phototrophic growth (H-1); (2) the additional use of dissolved organic carbon (mixotrophy) leads to higher growth rates under IC-limitation (H-2), and (3) phagotrophy is not relevant (H-3). H- 1 was supported as the culture experiments, in situ PAR and IC concentrations indicated that IC potentially limited phototrophic growth in the mixed surface layers. H-2 was also supported: mixotrophic growth always exceeded pure phototrophic growth even when photosynthesis was saturated. Dark growth in filtered lake water illuminated prior to inoculation provided evidence that Chlamydomonas was able to use the natural DOC. The alga did not grow on bacteria, thus confirming H-3. Chlamydomonas exhibited a remarkable resistance to starvation in the dark. The compensation light intensity (ca. 20 mu mol photons m(-2) s(-1)) and the maximum phototrophic growth (1.50 d(-1)) fell within the range of algae from non-acidic waters. Overall, Chlamydomonas, a typical r-strategist in circum-neutral systems, showed characteristics of a K-strategist in the stable, acidic lake environment in achieving moderate growth rates and minimizing metabolic losses. (c) 2005 Elsevier GmbH. All rights reserved},
  language  = {en}
}
@article{KamjunkeStraileGaedke2009,
  author    = {Kamjunke, Norbert and Straile, Dietmar and Gaedke, Ursula},
  title     = {Response of heterotrophic bacteria, autotrophic picoplankton and heterotrophic nanoflagellates to re- oligotrophication},
  issn      = {0142-7873},
  doi       = {10.1093/plankt/fbp037},
  year      = {2009},
  abstract  = {We investigated the response of the microbial components of the pelagic food web to re-oligotrophication of large, deep Lake Constance where total phosphorus concentrations during mixing decreased from a maximum of 2.81 mu mol L- 1 in 1979 via 1.87 mu mol L-1 in 1987 to 0.26 mu mol L-1 in 2007. Measurements of heterotrophic bacteria, autotrophic picoplankton (APP) and heterotrophic nanoflagellates (HNF) in 2006 and 2007 were compared to values from 1987 to 1997. We hypothesized that the biomass and seasonal variability of all groups will decrease under more oligotrophic conditions due to reduced resource availability, particularly for APP and HNF but less for the competitively stronger bacteria. Average bacterial biomass between spring and autumn was unrelated to phosphorus, whereas the ratio of bacterial biomass to chlorophyll a concentration increased with decreasing trophy due to declining chlorophyll concentrations. In contrast, a unimodal relationship was found between APP and phosphorus with low biomass at low and high phosphorus concentrations and maximum biomass in between. Average HNF biomass decreased strongly by a factor of 10-30 with decreasing trophy, and chlorophyll-specific HNF biomass was unimodally related to phosphorus. The relative seasonal biomass variability did not change for any group during re-oligotrophication. To conclude, HNF responded much more strongly and bacteria less so than chlorophyll concentrations to oligotrophication, whereas APP exhibited a more complex pattern.},
  language  = {en}
}
@article{KamjunkeGaedkeTitteletal.2004,
  author    = {Kamjunke, Norbert and Gaedke, Ursula and Tittel, J{\"o}rg and Weithoff, Guntram and Bell, Elanor M.},
  title     = {Strong vertical differences in the plankton composition of an extremely acidic lake},
  year      = {2004},
  abstract  = {Vertical differences in food web structure were examined in an extremely acidic, iron-rich mining lake in Germany (Lake 111; pH 2.6, total Fe 150mg L-1) during the period of stratification. We tested whether or not the seasonal variation of the plankton composition is less pronounced than the differences observed over depth. The lake was strongly stratified in summer, and concentrations of dissolved organic carbon and inorganic carbon were consistently low in the epilimnion but high in the hypolimnion. Oxygen concentrations declined in the hypolimnion but were always above 2mg L-1. Light attenuation did not change over depth and time and was governed by dissolved ferric iron. The plankton consisted mainly of single-celled and filamentous bacteria, the two mixotrophic flagellates Chlamydomonas sp. and Ochromonas sp., the two rotifer species Elosa worallii and Cephalodella hoodi, and Heliozoa as top predators. We observed very few ciliates and rhizopods, and no heterotrophic flagellates, crustaceans or fish. Ochromonas sp., bacterial filaments, Elosa and Heliozoa dominated in the epilimnion whereas Chlamydomonas sp., single-celled bacteria and Cephalodella dominated in the hypolimnion. Single-celled bacteria were controlled by Ochromonas sp. whereas the lack of large consumers favoured a high proportion of bacterial filaments. The primarily phototrophic Chlamydomas sp. was limited by light and CO2 and may have been reduced due to grazing by Ochromonas sp. in the epilimnion. The distribution of the primarily phagotrophic Ochromonas sp. and of the animals seemed to be controlled by prey availability. Differences in the plankton composition were much higher between the epilimnion and hypolimnion than within a particular stratum over time. The food web in Lake 111 was extremely species-poor enabling no functional redundancy. This was attributed to the direct exclusion of species by the harsh environmental conditions and presumably enforced by competitive exclusion. The latter was promoted by the low diversity at the first trophic level which, in turn, was attributed to relatively stable growth conditions and the independence of resource availability (inorganic carbon and light) from algal density. Ecological theory suggests that low functional redundancy promotes low stability in ecosystem processes which was not supported by our data.},
  language  = {en}
}
@article{KamjunkeGaedke2007,
  author    = {Kamjunke, Norbert and Gaedke, Ursula},
  title     = {Phosphorus gain by bacterivory promotes the mixotrophic flagellate Dinobryon spp. during re-oligotrophication},
  issn      = {0142-7873},
  doi       = {10.1093/plankt/fb1054},
  year      = {2007},
  abstract  = {Bacterivory by mixotrophic flagellates may contribute to their nutrient supply, providing a competitive advantage in oligotrophic waters. We hypothesized an increase in Dinobryon biomass during the re-oligotrophication process in the large and deep Lake Constance. To estimate whether bacterivory contributed substantially to the flagellates' phosphorus supply, we determined ingestion rates. Dinobryon biomass increased with decreasing total phosphorus concentrations in the lake over a period of 17 years (P = 0.0005). The promotion of Dinobryon biomass during re-oligotrophication may be explained by the increasing light availability due to the decreasing biomass of other phytoplankton yielding a release from competition. The date of the Dinobryon abundance maximum shifted to earlier time points in the year, probably because a smaller phosphorus pool was depleted more quickly. Ingestion rates of Dinobryon ranged between 0.5 and 13 bacteria cell(-1) h(-1) (0.2-5.4 fg C pg C-1 h(-1)), and clearance rates varied between 0.2 and 3.2 nL cell(-1) h(-1) (4-78 pL pg C-1 h(-1)), leading to bacterial losses of up to 30\% day(-1) of bacterial standing stock. The ingestion of bacteria covered 77\% of the phosphorus need of the flagellate during the period of maximum growth in 1996 (net growth rate 0.34 day(-1)), and it fully covered the need at all other times.},
  language  = {en}
}
@article{GaedkeKamjunke2006,
  author    = {Gaedke, Ursula and Kamjunke, Norbert},
  title     = {Structural and functional properties of low- and high-diversity planktonic food webs},
  issn      = {0142-7873},
  doi       = {10.1093/plankt/fb1003},
  year      = {2006},
  abstract  = {To test the consequences of decreased diversity and exclusion of keystone species, we compared the planktonic food webs in two acidic (pH <= 3), species-poor mining lakes with those in two species-rich, neutral lakes. The ratio of heterotrophic to autotrophic biomass (HIA) was similar in acidic and neutral lakes with comparable productivity. However, food webs in both acidic lakes were largely restricted to two trophic levels in contrast to the four levels found in neutral lakes. This restriction in food chain length was attributed to the absence of efficient secondary consumers, rather than to productivity or lake size which resulted in unusually low predator-prey weight ratios, with small top predators hardly exceeding their pry in size. In contrast to the neutral lakes, plankton biomass size spectra of acidic lakes were discontinuous due to a lack of major functional groups. The unique size-dependence of feeding modes in pelagic food webs, with bacteria in the smallest size classes followed by autotrophs, herbivores and carnivores, was maintained for bacteria but the other feeding modes strongly overlapped in size. Thus, their characteristic succession along the size gradient was roughly preserved under extreme conditions but the flow of energy along the size gradient was truncated in the acidic lakes. For most but not all attributes studied, differences were larger between acidic and neutral lakes than between neutral lakes of different trophic state},
  language  = {en}
}