TY - JOUR A1 - Bickel, Samantha L. A1 - Tang, Kam W. A1 - Grossart, Hans-Peter T1 - Ciliate epibionts associated with crustacean zooplankton in German lakes - distribution, motility, and bacterivory JF - Frontiers in microbiology N2 - Ciliate epibionts associated with crustacean zooplankton are widespread in aquatic systems, but their ecological roles are little known. We studied the occurrence of ciliate epibionts on crustacean zooplankton in nine German lakes with different limnological features during the summer of 2011. We also measured the detachment and re-attachment rates of the ciliates, changes in their motility, and the feeding rates of attached vs. detached ciliate epibionts. Epibionts were found in all lakes sampled except an acidic lake with large humic inputs. Epibiont prevalence was as high as 80.96% on the cladoceran Daphnia cucullata, 67.17% on the cladoceran Diaphanosoma brachyurum, and 46.67% on the calanoid copepod Eudiaptomus gracilis. Both cladoceran groups typically had less than 10 epibionts per individual, while the epibiont load on E. gracilis ranged from 1 to >30 epibionts per individual. After the death of the zooplankton host, the peritrich ciliate epibiont Epistylis sp. detached in an exponential fashion with a half-life of 5 min, and 98% detached within 30 min, leaving behind the stalks used for attachment. Immediately after detachment, the ciliates were immotile, but 62% became motile within 60 min. When a new host was present, only 27% reattached after 120 min. The average measured ingestion rate and clearance rate of Epistylis were 11,745 bacteria ciliate(-1) h(-1) and 24.33 mu l ciliate(-1) h(-1), respectively. Despite their high feeding rates, relatively low epibiont abundances were observed in the field, which suggests either diversion of energy to stalk formation, high metabolic loss by the epibionts, or high mortality among the epibiont populations. KW - ciliate epibionts KW - Epistylis KW - crustacean zooplankton KW - bacterivory KW - epibiont motility Y1 - 2012 U6 - https://doi.org/10.3389/fmicb.2012.00243 SN - 1664-302X VL - 3 PB - Frontiers Research Foundation CY - Lausanne ER - TY - JOUR A1 - Günthel, Marco A1 - Donis, Daphne A1 - Kirillin, Georgiy A1 - Ionescu, Danny A1 - Bizic, Mina A1 - McGinnis, Daniel F. A1 - Grossart, Hans-Peter A1 - Tang, Kam W. T1 - Contribution of oxic methane production to surface methane emission in lakes and its global importance JF - Nature Communications N2 - Recent discovery of oxic methane production in sea and lake waters, as well as wetlands, demands re-thinking of the global methane cycle and re-assessment of the contribution of oxic waters to atmospheric methane emission. Here we analysed system-wide sources and sinks of surface-water methane in a temperate lake. Using a mass balance analysis, we show that internal methane production in well-oxygenated surface water is an important source for surface-water methane during the stratified period. Combining our results and literature reports, oxic methane contribution to emission follows a predictive function of littoral sediment area and surface mixed layer volume. The contribution of oxic methane source(s) is predicted to increase with lake size, accounting for the majority (>50%) of surface methane emission for lakes with surface areas >1 km(2). Y1 - 2019 U6 - https://doi.org/10.1038/s41467-019-13320-0 SN - 2041-1723 VL - 10 PB - Nature Publishing Group UK CY - London ER - TY - JOUR A1 - Glud, Ronnie N. A1 - Grossart, Hans-Peter A1 - Larsen, Morten A1 - Tang, Kam W. A1 - Arendt, Kristine E. A1 - Rysgaard, Soren A1 - Thamdrup, Bo A1 - Gissel Nielsen, Torkel T1 - Copepod carcasses as microbial hot spots for pelagic denitrification JF - Limnology and oceanography N2 - Copepods are exposed to a high non-predatory mortality and their decomposing carcasses act as microniches with intensified microbial activity. Sinking carcasses could thereby represent anoxic microenvironment sustaining anaerobic microbial pathways in otherwise oxic water columns. Using non-invasive O-2 imaging, we document that carcasses of Calanus finmarchicus had an anoxic interior even at fully air-saturated ambient O-2 level. The extent of anoxia gradually expanded with decreasing ambient O-2 levels. Concurrent microbial sampling showed the expression of nitrite reductase genes (nirS) in all investigated carcass samples and thereby documented the potential for microbial denitrification in carcasses. The nirS gene was occasionally expressed in live copepods, but not as consistently as in carcasses. Incubations of sinking carcasses in (15)NO3-amended seawater demonstrated denitrification, of which on average 34%+/- 17% (n=28) was sustained by nitrification. However, the activity was highly variable and was strongly dependent on the ambient O-2 levels. While denitrification was present even at air-saturation (302 mol L-1), the average carcass specific activity increased several orders of magnitude to approximate to 1 nmol d(-1) at 20% air-saturation (55 mol O-2 L-1) at an ambient temperature of 7 degrees C. Sinking carcasses of C. finmarchicus therefore represent hotspots of pelagic denitrification, but the quantitative importance as a sink for bioavailable nitrogen is strongly dependent on the ambient O-2 level. The importance of carcass associated denitrification could be highly significant in O-2 depleted environments such as Oxygen Minimum Zones (OMZ). Y1 - 2015 U6 - https://doi.org/10.1002/lno.10149 SN - 0024-3590 SN - 1939-5590 VL - 60 IS - 6 SP - 2026 EP - 2036 PB - Wiley-Blackwell CY - Hoboken ER - TY - JOUR A1 - Tang, Kam W. A1 - Backhaus, Liv A1 - Riemann, Lasse A1 - Koski, Marja A1 - Grossart, Hans-Peter A1 - Munk, Peter A1 - Nielsen, Torkel Gissel T1 - Copepod carcasses in the subtropical convergence zone of the Sargasso Sea BT - implications for microbial community composition, system respiration and carbon flux JF - Journal of plankton research N2 - The oligotrophic subtropical gyre covers a vast area of the Atlantic Ocean. Decades of time-series monitoring have generated detailed temporal information about zooplankton species and abundances at fixed locations within the gyre, but their live/dead status is often omitted, especially in the dynamic subtropical convergence zone (STCZ) where the water column stratification pattern can change considerably across the front as warm and cold water masses converge. We conducted a detailed survey in the North Atlantic STCZ and showed that over 85% of the copepods were typically concentrated in the upper 200 m. Copepod carcasses were present in all samples and their proportional numerical abundances increased with depth, reaching up to 91% at 300-400 m. Overall, 14-19% of the copepods within the upper 200 m were carcasses. Shipboard experiments showed that during carcass decomposition, microbial respiration increased, and the bacterial community associated with the carcasses diverged from that in the ambient water. Combining field and experimental data, we estimated that decomposing copepod carcasses constitute a negligible oxygen sink in the STCZ, but sinking carcasses may represent an overlooked portion of the passive carbon sinking flux and should be incorporated in future studies of carbon flux in this area. KW - Sargasso Sea KW - subtropical convergence zone KW - zooplankton KW - carcasses KW - carbon sinking flux Y1 - 2019 U6 - https://doi.org/10.1093/plankt/fbz038 SN - 0142-7873 SN - 1464-3774 VL - 41 IS - 4 SP - 549 EP - 560 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Tolomeev, Aleksandr P. A1 - Dubovskaya, Olga P. A1 - Kirillin, Georgiy A1 - Buseva, Zhanna A1 - Kolmakova, Olesya A1 - Grossart, Hans-Peter A1 - Tang, Kam W. A1 - Gladyšev, Michail I. T1 - Degradation of dead cladoceran zooplankton and their contribution to organic carbon cycling in stratified lakes BT - field observation and model prediction JF - Journal of plankton research N2 - The contribution of dead zooplankton biomass to carbon cycle in aquatic ecosystems is practically unknown. Using abundance data of zooplankton in water column and dead zooplankton in sediment traps in Lake Stechlin, an ecological-mathematical model was developed to simulate the abundance and sinking of zooplankton carcasses and predict the related release of labile organic matter (LOM) into the water column. We found species-specific differences in mortality rate of the dominant zooplankton: Daphnia cucullata, Bosmina coregoni and Diaphanosoma brachyurum (0.008, 0.129 and 0.020 day(-1), respectively) and differences in their carcass sinking velocities in metalimnion (and hypolimnion): 2.1 (7.64), 14.0 (19.5) and 1.1 (5.9) m day(-1), respectively. Our model simulating formation and degradation processes of dead zooplankton predicted a bimodal distribution of the released LOM: epilimnic and metalimnic peaks of comparable intensity, ca. 1 mg DW m(-3) day(-1). Maximum degradation of carcasses up to ca. 1.7 mg DW m(-3) day(-1) occurred in the density gradient zone of metalimnion. LOM released from zooplankton carcasses into the surrounding water may stimulate microbial activity and facilitate microbial degradation of more refractory organic matter; therefore, dead zooplankton are expected to be an integral part of water column carbon source/sink dynamics in stratified lakes. KW - zooplankton carcasses KW - non-predatory mortality KW - sinking velocities KW - microbial degradation KW - Lake Stechlin KW - simulation modeling Y1 - 2022 U6 - https://doi.org/10.1093/plankt/fbac023 SN - 0142-7873 SN - 1464-3774 VL - 44 IS - 3 SP - 386 EP - 400 PB - Oxford Univ. Press CY - Oxford ER - TY - JOUR A1 - Dziallas, Claudia A1 - Grossart, Hans-Peter A1 - Tang, Kam W. A1 - Nielsen, Torkel Gissel T1 - Distinct Communities of Free-Living and Copepod-Associated Microorganisms along a Salinity Gradient in Godthabsfjord, West Greenland JF - ARCTIC ANTARCTIC AND ALPINE RESEARCH N2 - Microorganisms such as Bacteria and Archaea play important roles in the Arctic food web and biogeochemical cycles. Nevertheless, knowledge of microbial community composition in Greenland waters is scarce, and information on microorganisms associated with Arctic zooplankton species is virtually non-existent. We compared free-living microbial communities with those associated with two key copepod species (Calanus finmarchicus and Metridia longa) along a salinity gradient from the deep waters beyond Fyllas Banke to the inner part of Godthabsfjord, West Greenland, in summer 2008. Using genetic fingerprinting we found that free-living Bacteria (in particular Alphaproteobacteria) and Archaea varied with environmental factors and formed different communities along the fjord. Microbial communities associated with the two copepod species were clearly different from those in the ambient water. Surprisingly, Archaea could not be detected on the copepods. Our results show that zooplankton form "microbial islands" in the Arctic pelagic realm with a distinctive community composition and presumably functionality different from the free-living Bacteria. Changes in intensity and timing of meltwater runoff due to global warming are expected to affect these microbial assemblages differently, with potentially significant ramifications for Arctic food webs and biogeochemistry. Y1 - 2013 U6 - https://doi.org/10.1657/1938-4246.45.4.471 SN - 1523-0430 SN - 1938-4246 VL - 45 IS - 4 SP - 471 EP - 480 PB - INST ARCTIC ALPINE RES CY - BOULDER ER - TY - GEN A1 - Dubovskaya, Olga P. A1 - Tang, Kam W. A1 - Gladyshev, Michail I. A1 - Kirillin, Georgiy A1 - Buseva, Zhanna A1 - Kasprzak, Peter A1 - Tolomeev, Aleksandr P. A1 - Grossart, Hans-Peter T1 - Estimating in situ zooplankton non-predation mortality in an oligo-mesotrophic lake from sediment trap data BT - caveats and reality check T2 - Postprints der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe N2 - Background Mortality is a main driver in zooplankton population biology but it is poorly constrained in models that describe zooplankton population dynamics, food web interactions and nutrient dynamics. Mortality due to non-predation factors is often ignored even though anecdotal evidence of non-predation mass mortality of zooplankton has been reported repeatedly. One way to estimate non-predation mortality rate is to measure the removal rate of carcasses, for which sinking is the primary removal mechanism especially in quiescent shallow water bodies. Objectives and Results We used sediment traps to quantify in situ carcass sinking velocity and non-predation mortality rate on eight consecutive days in 2013 for the cladoceran Bosmina longirostris in the oligo-mesotrophic Lake Stechlin; the outcomes were compared against estimates derived from in vitro carcass sinking velocity measurements and an empirical model correcting in vitro sinking velocity for turbulence resuspension and microbial decomposition of carcasses. Our results show that the latter two approaches produced unrealistically high mortality rates of 0.58-1.04 d(-1), whereas the sediment trap approach, when used properly, yielded a mortality rate estimate of 0.015 d(-1), which is more consistent with concurrent population abundance data and comparable to physiological death rate from the literature. Ecological implications Zooplankton carcasses may be exposed to water column microbes for days before entering the benthos; therefore, non-predation mortality affects not only zooplankton population dynamics but also microbial and benthic food webs. This would be particularly important for carbon and nitrogen cycles in systems where recurring mid-summer decline of zooplankton population due to non-predation mortality is observed. T3 - Zweitveröffentlichungen der Universität Potsdam : Mathematisch-Naturwissenschaftliche Reihe - 501 KW - fresh-water KW - nonconsumptive mortality KW - crustacean zooplankton KW - nonpredatory mortality KW - siberian reservoir KW - seasonal dynamics KW - copepod carcasses KW - sinking speed KW - aniline blue KW - marine snow Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus4-408392 SN - 1866-8372 IS - 501 ER - TY - JOUR A1 - Dubovskaya, Olga P. A1 - Tang, Kam W. A1 - Gladyshev, Michail I. A1 - Kirillin, Georgiy A1 - Buseva, Zhanna A1 - Kasprzak, Peter A1 - Tolomeev, Aleksandr P. A1 - Grossart, Hans-Peter T1 - Estimating In Situ Zooplankton Non-Predation Mortality in an Oligo-Mesotrophic Lake from Sediment Trap Data: Caveats and Reality Check JF - PLoS one N2 - Background Mortality is a main driver in zooplankton population biology but it is poorly constrained in models that describe zooplankton population dynamics, food web interactions and nutrient dynamics. Mortality due to non-predation factors is often ignored even though anecdotal evidence of non-predation mass mortality of zooplankton has been reported repeatedly. One way to estimate non-predation mortality rate is to measure the removal rate of carcasses, for which sinking is the primary removal mechanism especially in quiescent shallow water bodies. Objectives and Results We used sediment traps to quantify in situ carcass sinking velocity and non-predation mortality rate on eight consecutive days in 2013 for the cladoceran Bosmina longirostris in the oligo-mesotrophic Lake Stechlin; the outcomes were compared against estimates derived from in vitro carcass sinking velocity measurements and an empirical model correcting in vitro sinking velocity for turbulence resuspension and microbial decomposition of carcasses. Our results show that the latter two approaches produced unrealistically high mortality rates of 0.58-1.04 d(-1), whereas the sediment trap approach, when used properly, yielded a mortality rate estimate of 0.015 d(-1), which is more consistent with concurrent population abundance data and comparable to physiological death rate from the literature. Ecological implications Zooplankton carcasses may be exposed to water column microbes for days before entering the benthos; therefore, non-predation mortality affects not only zooplankton population dynamics but also microbial and benthic food webs. This would be particularly important for carbon and nitrogen cycles in systems where recurring mid-summer decline of zooplankton population due to non-predation mortality is observed. Y1 - 2015 U6 - https://doi.org/10.1371/journal.pone.0131431 SN - 1932-6203 VL - 10 IS - 7 PB - PLoS CY - San Fransisco ER - TY - JOUR A1 - Tang, Kam W. A1 - McGinnis, Daniel F. A1 - Ionescu, Danny A1 - Großart, Hans-Peter T1 - Methane Production in Oxic Lake Waters Potentially Increases Aquatic Methane Flux to Air JF - Physical chemistry, chemical physics : a journal of European Chemical Societies N2 - Active methane production in oxygenated lake waters challenges the long-standing paradigm that microbial methane production occurs only under anoxic conditions and forces us to rethink the ecology and environmental dynamics of this powerful greenhouse gas. Methane production in the upper oxic water layers places the methane source closer to the air water interface, where convective mixing and microbubble detrainment can lead to a methane efflux higher than that previously assumed. Microorganisms may produce methane in oxic environments by being equipped with enzymes to counteract the effects of molecular oxygen during methanogenesis or using alternative pathways that do not involve oxygen-sensitive enzymes. As this process appears to be influenced by thermal stratification, water transparency, and primary production, changes in lake ecology due to climate change will alter methane formation in oxic water layers, with far-reaching consequences for methane flux and climate feedback. Y1 - 2016 U6 - https://doi.org/10.1021/acs.estlett.6b00150 SN - 2328-8930 VL - 3 SP - 227 EP - 233 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Grossart, Hans-Peter A1 - Frindte, Katharina A1 - Dziallas, Claudia A1 - Eckert, Werner A1 - Tang, Kam W. T1 - Microbial methane production in oxygenated water column of an oligotrophic lake JF - Proceedings of the National Academy of Sciences of the United States of America N2 - The prevailing paradigm in aquatic science is that microbial methanogenesis happens primarily in anoxic environments. Here, we used multiple complementary approaches to show that microbial methane production could and did occur in the well-oxygenated water column of an oligotrophic lake (Lake Stechlin, Germany). Oversaturation of methane was repeatedly recorded in the well-oxygenated upper 10 m of the water column, and the methane maxima coincided with oxygen oversaturation at 6 m. Laboratory incubations of unamended epilimnetic lake water and inoculations of photoautotrophs with a lake-enrichment culture both led to methane production even in the presence of oxygen, and the production was not affected by the addition of inorganic phosphate or methylated compounds. Methane production was also detected by in-lake incubations of lake water, and the highest production rate was 1.8-2.4 nM.h(-1) at 6 m, which could explain 33-44% of the observed ambient methane accumulation in the same month. Temporal and spatial uncoupling between methanogenesis and methanotrophy was supported by field and laboratory measurements, which also helped explain the oversaturation of methane in the upper water column. Potentially methanogenic Archaea were detected in situ in the oxygenated, methane-rich epilimnion, and their attachment to photoautotrophs might allow for anaerobic growth and direct transfer of substrates for methane production. Specific PCR on mRNA of the methyl coenzyme M reductase A gene revealed active methanogenesis. Microbial methane production in oxygenated water represents a hitherto overlooked source of methane and can be important for carbon cycling in the aquatic environments and water to air methane flux. KW - epilimnic methane peak KW - methanogens Y1 - 2011 U6 - https://doi.org/10.1073/pnas.1110716108 SN - 0027-8424 VL - 108 IS - 49 SP - 19657 EP - 19661 PB - National Acad. of Sciences CY - Washington ER -