Increased Zooplankton Grazing Research Articles

Alpha-glucans from bacterial necromass indicate an intra-population loop within the marine carbon cycle

Phytoplankton blooms provoke bacterioplankton blooms, from which bacterial biomass (necromass) is released via increased zooplankton grazing and viral lysis. While bacterial consumption of algal biomass during blooms is well-studied, little is known about the concurrent recycling of these substantial amounts of bacterial necromass. We demonstrate that bacterial biomass, such as bacterial alpha-glucan storage polysaccharides, generated from the consumption of algal organic matter, is reused and thus itself a major bacterial carbon source in vitro and during a diatom-dominated bloom. We highlight conserved enzymes and binding proteins of dominant bloom-responder clades that are presumably involved in the recycling of bacterial alpha-glucan by members of the bacterial community. We furthermore demonstrate that the corresponding protein machineries can be specifically induced by extracted alpha-glucan-rich bacterial polysaccharide extracts. This recycling of bacterial necromass likely constitutes a large-scale intra-population energy conservation mechanism that keeps substantial amounts of carbon in a dedicated part of the microbial loop.

Regime shift in microalgal dynamics: Impact of water level changes on planktonic and benthic algal biomass

Whole-lake microalgal biomass surveys were carried out in Lake Balaton to investigate the seasonal, spatial, and temporal changes of benthic algae, as well as to identify the drivers of the phytobenthos. Phytobenthos was controlled mainly by light: the highest benthic algal biomass was in the shallow littoral region characterized by large grain size (sand) with good light availability but lower nutrient content in the sediment. During the investigated period, phytoplankton biomass showed a significant decrease in almost the entire lake. At the same time, the biomass of benthic algae increased significantly in the eastern areas, increasing the contribution of total lake microalgae biomass (from 20 % to 27 %). Benthic algal biomass increase can be explained by the better light supply, owing to the artificially maintained high water level which greatly mitigates water mixing. The decrease in planktonic algal biomass could be attributed to increased zooplankton grazing, which is otherwise negatively affected by mixing. As a result of the high water level, the trophic structure of the lake has been rearranged in recent decades with a shift from the planktonic life form to the benthic one while the nutrient supply has largely remained unchanged.

Combined effects of increased water temperature and cyanobacterial compounds exert heterogeneous effects on survival and ecological processes in key freshwater species

Climate change is increasing water temperature and intensifying the incidence of cyanobacterial blooms worldwide. However, the combined effects of increased temperature and microcystin concentrations as co-stressors on survival and ecological processes in freshwater species are unclear. Here, using purified MC-LR and crude extract of toxigenic Microcystis aeruginosa, we tested the individual and combined effects of three water temperatures (15, 20, 25 °C) and a range of environmentally relevant concentrations of dissolved microcystin and crude extract (0.01–10 µg·L−1) on survival, growth inhibition, grazing and predation rates in three freshwater species: phytoplankton (Scenedesmus quadricauda), zooplankton (Daphnia pulex), and an invertebrate predator (Ischnura elegans). Purified MC-LR exerted a higher growth inhibitory effect on S. quadricauda compared to crude extract with the same concentration of MC-LR, while neither treatment affected its chlorophyll-a content or survival of D. pulex. Crude extract reduced grazing and survival of D. pulex and I. elegans, respectively. The combined effect of higher temperature and crude extract reduced I. elegans survival by 50%. Increased temperature reduced prey handing time in I. elegans by 49%, suggesting a higher predation rate. However, warming together with higher concentrations of crude extract jointly increased zooplankton grazing and reduced damselfly predation. Taken together, these results suggest crude extract, and not necessarily microcystin, can affect survival and productivity in freshwater species, although these effects may vary unevenly across trophic levels. Our findings highlight the importance of complex ecological mechanisms by which warming can exacerbate toxic effects of cyanobacterial bloom extracts on survival and functions among species in eutrophic freshwaters.

Projecting the effects of climate-driven changes in organic matter supply on benthic food webs in the northern Bering Sea

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 548:11-30 (2016) - DOI: https://doi.org/10.3354/meps11651 Projecting the effects of climate-driven changes in organic matter supply on benthic food webs in the northern Bering Sea James R. Lovvorn1,*, Christopher A. North2,5, Jason M. Kolts2,6, Jacqueline M. Grebmeier3, Lee W. Cooper3, Xuehua Cui4 1Department of Zoology and Center for Ecology, Southern Illinois University, Carbondale, Illinois 62901, USA 2Department of Zoology and Physiology, University of Wyoming, Laramie, Wyoming 82071, USA 3Chesapeake Biological Laboratory, University of Maryland Center for Environmental Science, Solomons, Maryland 20688, USA 4Department of Ecology and Evolutionary Biology, University of Tennessee, Knoxville, Tennessee 37996, USA 5Present address: Department of Botany, University of Wyoming, Laramie, Wyoming 82071, USA 6Present address: Department of Biology, Metropolitan State University of Denver, Denver, Colorado 80217, USA *Corresponding author: lovvorn@siu.edu ABSTRACT: Climate-driven changes in seasonal sea ice are expected to affect the timing, magnitude, and fate of phytoplankton production. Production may be increased by longer ice-free periods, or decreased by reduced stratification of the water column without freshwater input from melting ice. Benthic deposit-feeders may experience changes in organic matter (OM) supply owing to altered phytoplankton production, increased zooplankton grazing, or redistribution of settling phytodetritus. Where most benthic taxa subsist on a longer-term pool of sediment OM and bacteria, communities may be partially buffered against varied inputs of phytodetritus. We used network models of benthic food webs in 3 sectors of the northern Bering Sea to simulate effects of changes in OM supply. In the models, sediment OM content, which integrates longer-term inputs of microalgae, was gradually reduced or increased over 10 yr to the lowest or highest levels observed among sampling stations. In both samples and model predictions, decreased sediment OM was linked to quite variable declines among trophic groups, with effective loss of some taxa. Increased sediment OM was coupled with moderate to dramatic increases of different taxa, sometimes with lagged peaks and declines of prey and predators. In the models, meiofauna, protists, and bacteria responded quickly, while macrofauna exhibited 2 yr delays, suggesting short-term but limited buffering by the sediment OM pool. Our results indicate that climate-related changes in phytodetrital inputs can lead to important shifts in benthic biomass, community structure, and functional diversity, with loss of various common taxa. KEY WORDS: Benthic communities · Deposit-feeders · Food web limitation · Food web models · Network models · Phytodetritus · Sediment organic matter Full text in pdf format PreviousNextCite this article as: Lovvorn JR, North CA, Kolts JM, Grebmeier JM, Cooper LW, Cui X (2016) Projecting the effects of climate-driven changes in organic matter supply on benthic food webs in the northern Bering Sea. Mar Ecol Prog Ser 548:11-30. https://doi.org/10.3354/meps11651 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 548. Online publication date: April 21, 2016 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2016 Inter-Research.

Effects of sea surface warming on marine plankton

Ocean warming has been implicated in the observed decline of oceanic phytoplankton biomass. Some studies suggest a physical pathway of warming via stratification and nutrient flux, and others a biological effect on plankton metabolic rates; yet the relative strength and possible interaction of these mechanisms remains unknown. Here, we implement projections from a global circulation model in a mesocosm experiment to examine both mechanisms in a multi-trophic plankton community. Warming treatments had positive direct effects on phytoplankton biomass, but these were overcompensated by the negative effects of decreased nutrient flux. Zooplankton switched from phytoplankton to grazing on ciliates. These results contrast with previous experiments under nutrient-replete conditions, where warming indirectly reduced phytoplankton biomass via increased zooplankton grazing. We conclude that the effect of ocean warming on marine plankton depends on the nutrient regime, and provide a mechanistic basis for understanding global change in marine ecosystems.

Can Submerged Macrophytes Influence Turbidity and Trophic State in Deep Lakes? Suggestions from a Case Study

Feedback between submerged macrophytes and water transparency stabilizing the clear, macrophyte-dominated regime has been described so far for shallow lakes. Based on data of total phosphorus (TP) concentrations, underwater light supply, phytoplankton and submerged macrophyte abundance from narrow, stratified Lake Scharmützelsee (mean depth: 9 m, retention time: 16 yr) of the period 1994-2006 we hypothesize that submerged macrophytes may influence transparency and trophic state in deep lakes. The lake was characterized by summer epilimnion TP concentrations of 38 to 57 mug L(-1), turbid water due to mass development of cyanobacteria, and low abundance of few submerged macrophyte species until 2003. Thereafter, a sudden increase in water transparency was followed by a rapid submerged macrophyte colonization of the littoral down to about 5 m depth corresponding to the depth of a light supply of 3 E m(-2) d(-1). Initially, this recolonization was probably a consequence of decreased turbidity. We argue that the increase of submerged macrophyte coverage from < 10% in 1994 to 2003 to about 24% in 2005-2006 has contributed to the stabilization of the clear-water regime during the subsequent years. This is supported by the fact that earlier shifts to clear-water regimes in 1994 and 2000 without a significant spread of submerged macrophytes were not stable. We discuss potential mechanisms that may have resulted in a positive effect of plants on transparency such as P uptake and immobilization by the dominant rootless macrophyte species Nitellopsis obtusa and Ceratophyllum demersum and other macrophyte-related mechanisms such as increased zooplankton grazing and allelopathy.

The Water Framework Directive: Setting the phosphorus loading target for a deep lake in Denmark using the 1D lake ecosystem model DYRESM–CAEDYM

We used the one-dimensional DYRESM–CAEDYM model to elucidate and quantify the influence of the external phosphorus loading on ecosystem dynamics in moderately deep Lake Ravn, which is situated in an agricultural landscape in Denmark. Model simulations were used to quantify the extent to which the external phosphorus loading must be reduced to meet upcoming lake ecological quality requirements according to the European Union Water Framework Directive (WFD). The model generally showed good agreement with observed data for temperature and oxygen from the epilimnion and hypolimnion during the calibration period (7 years) as well as the validation period (5 years); although peaks of oxygen concentrations in epilimnion during late spring often were underestimated. Phosphate and total phosphorus (TP) concentrations were generally well reproduced in both the epilimnion and hypolimnion, though hypolimnetic phosphorus was occasionally underestimated in late summer. There was also good agreement between monitored data and modelled biomass of diatoms and dinoflagellates as well as the zooplankton biomass of cladocerans and calanoid copepods, although the timing of biomass peaks occasionally deviated from observations. Root-mean-square-errors (RMSE), used to quantify the model error, were overall similar for the calibration and the validation period. Simulations of scenarios with a reduced external TP loading suggest that a substantial reduction (40–50%) of the TP loading is required if phytoplankton biomass is to drop to a level sufficiently low to meet the proposed WFD requirements (summer average <6.5 μg chlorophyll a l −1). The predicted outcomes of considerable loading reductions should, however, be treated with some caution, as the conceptual model in this study could not fully account for the changes in trophic structure occurring at radically reduced TP loading. This particularly applies to changes in the fish stock, which may have extensive cascading effects via increased zooplankton grazing on the phytoplankton when external TP loading is reduced. This would most likely lead to higher transparency than that predicted by the model. To further improve the reliability of the predicted outcomes of various model scenarios, future work should include a series of test simulations also including fish predation. Today, fish predation is available in the DYRESM–CAEDYM model as well as other dynamic lake models; however, only sparse data is available on fish stock dynamics in Lake Ravn (as for most other lakes). An applicable test of the fish algorithms in today’s dynamic models will require reliable estimates of fish stock biomass in the study lakes during both the model calibration and validation period.

A Review of Nontraditional Biomanipulation

The aim of this review is to identify problems, find general patterns, and extract recommendations for successful management using nontraditional biomanipulation to improve water quality. There are many obstacles that prevent traditional biomanipulation from achieving expectations: expending largely to remove planktivorous fish, reduction of external and internal phosphorus, and macrophyte re-establishment. Grazing pressure from large zooplankton is decoupled in hypereutrophic waters where cyanobacterial blooms flourish. The original idea of biomanipulation (increased zooplankton grazing rate as a tool for controlling nuisance algae) is not the only means of controlling nuisance algae via biotic manipulations. Stocking phytoplanktivorous fish may be considered to be a nontraditional method; however, it can be an effective management tool to control nuisance algal blooms in tropical lakes that are highly productive and unmanageable to reduce nutrient concentrations to low levels.Although small enclosures increase spatial overlap between predators and prey, leading to overestimates of the impact of predation, microcosm and whole-lake experiments have revealed similar community responses to major factors that regulate lake communities, such as nutrients and planktivorous fish. Both enclosure experiments and large-scale observations revealed that the initial phytoplankton community composition greatly impacted the success of biomanipulation. Long-term observations in Lake Donghu and Lake Qiandaohu have documented that silver carp (Hypophthalmichthys molitrix) and bighead carp (H. nobilis) (two filter-feeding planktivorous species commonly used in management) can suppress Microcystis blooms efficiently. The introduction of silver and bighead carp could be an effective management technique in eutrophic systems that lack macrozooplankton. We confirmed that nontraditional biomanipulation is only appropriate if the primary aim is to reduce nuisance blooms of large algal species, which cannot be controlled effectively by large herbivorous zooplankton. Alternatively, this type of biomanipulation did not work efficiently in less eutrophic systems where nanophytoplankton dominated.

Influences of the Gulf of Maine intrusion on the Massachusetts Bay spring bloom: A comparison between 1998 and 2000

The Boston Harbor, Massachusetts Bay and Cape Cod Bay system (MBS) is a semi-enclosed coastal embayment located in the western Gulf of Maine (GOM). The strength of the spring bloom in the MBS varies dramatically and the underlying mechanisms are not well understood. It has been hypothesized that the weak (or missing) 1998 spring bloom was due to increased zooplankton grazing pressure after a relatively warmer winter that led to earlier development of zooplankton populations. However, chlorophyll concentrations were low in the entire GOM region during the spring bloom period of 1998. These low chlorophyll waters would enter the MBS by persistent intrusion from the GOM and affect the MBS spring bloom by reducing the accumulation of phytoplankton biomass, suggesting an alternative explanation for the missing bloom. In this study, the influences of the intruding GOM waters on the MBS spring bloom are examined using numerical simulations and observations to compare two contrasting spring blooms (a weak bloom in 1998 versus a strong bloom in 2000). The results indicate that intruding waters from the GOM significantly reduced the strength of spring bloom in 1998, but enhanced the spring bloom in 2000. A theoretical analysis suggests that the influence of the intrusion on the MBS spring bloom is mostly limited to the northern portion of the MBS, and the impact area is determined by local net growth, velocity of intruding flow and horizontal mixing. The intrusion of GOM waters carries the signal of long-term variability in the GOM region and thus may be an important oceanic pathway for climate changes to impact the MBS ecosystem.

Impact of mass mortality of a mosquito fish, Gambusia affinis on the ecology of a fresh water eutrophic lake (Lake Naini Tal, India)

Between 28th March and 4th April, 2000 a fungal infection killed >80% of the most abundant planktivorous fish, Gambusia affinis in Lake Naini Tal, Uttaranchal, India. In response to this mortality, planktonic communities and some eutrophication-related parameters viz., primary productivity, phosphate–phosphorus, nitrate–nitrogen and transparency of the water, were considerably changed. Total zooplankton number more than doubled, phytoplankton number reduced nearly to half, primary production and phosphate-phosphorus was dramatically reduced, while nitrate–nitrogen and water clarity increased. The phytoplankton decline was caused by increased zooplankton grazing (top-down control) rather than phosphorus deficiency (bottom-up control). After 3 months, Gambusia and planktonic communities and nutrient levels reverted back almost to their pre-mortality state. Thus removal of G. affinis could improve water quality of Lake Naini Tal.

Practical success of biomanipulation using filter-feeding Fish to control cyanobacteria blooms: a synthesis of decades of research and application in a subtropical hypereutrophic lake.

337 Lake Donghu is a 32-km 2 shallow, subtropical lake near the Yangtze River (P.R. China) that has experienced dramatic changes in the past five decades. These changes include: (1) a trophic state change from mesotrophy to hypertrophy; (2) dense blooms of cyanobacteria during every summer from the 1970s to 1984; (3) a cessation of blooms starting in 1985, with no recurrence; and (4) an increase, coincident with bloom declines, in the production of silver and bighead carp (filter-feeders) by more than tenfold. There are several possible explanations for the disappearance of blooms, including changes in nutrient concentrations, increased zooplankton grazing, and increased grazing on algae by fish. The long-term data suggest that changes in nutrients or in zooplankton were not important, but that the remarkably increased fish densities might have played the key role. To test this hypothesis, in situ enclosure experiments were conducted in three years. The main conclusions are as follows: (1) an increased stocking of the lake with carp played a decisive role in the elimination of cyanobacteria blooms; (2) both silver and bighead carp can eliminate cyanobacteria blooms directly by grazing; (3) zooplankton cannot suppress the blooms; and (4) the lake still is vulnerable to the outbreak of blooms, should fish grazing decline. The critical biomass of carp is approximately 50 g m 3 . The results suggest the applicability of a new food-web manipulation (increased stocking with filter-feeding fish) for controlling cyanobacteria blooms in hypereutrophic lakes. The approach differs from traditional biomanipulation in Europe and North America, where piscivores are added to control planktivores, and this in turn increases zooplankton and decreases algae. The new biomanipulation method is being used or being tested to counteract cyanobacteria blooms in many Chinese lakes such as Lake Dianchi?Xie and Liu: Biomanipulation to Control Cyanobacteria TheScientificWorld (2001) 1, 337-356 in Yunnan Province, Lake Chaohu in Anhui Province, and Lake Taihu in Jiangsu Province. The method has great potential as an important component of an integrated approach to counteract cyanobacteria blooms, especially in lakes where nutrient inputs cannot be reduced sufficiently, and where zooplankton cannot effectively control phytoplankton production.

Zooplankton impacts on chlorophyll and transparency in Onondaga Lake, New York, USA

The transparency of polluted, hypereutrophic Onondaga Lake, New York, USA has improved substantially in the late 1980’s as a result of reductions in phytoplankton biomass, in the absence of significant reductions in external phosphorus loading. Much of this improvement has been due to the occurrence of clearing events, e.g. sudden and dramatic increases in transparency. Field measurements, laboratory experiments, and modelling analyses were utilized to identify processes regulating phytoplankton standing crop during the spring to fall interval of 1987. Changes in the zooplankton community documented over the past decade support the conclusion that increased zooplankton grazing has contributed to improvements in transparency. Herbivores now represent a greater fraction of the zooplankton population and more efficient cladocerans are present in greater numbers. Biomanipulation practices, e.g. reestablishment of piscivorous species, designed to reduce the abundance of planktivorous fish species in Onondaga Lake, may serve to reduce pressure on the grazing community and thus result in further improvements in transparency.

Phytoplankton biomass reduction after planktivorous fish reduction in a shallow, eutrophic lake: a combined effect of reduced internal P-loading and increased zooplankton grazing

Phytoplankton biomass reduction after planktivorous fish reduction in a shallow, eutrophic lake: a combined effect of reduced internal P-loading and increased zooplankton grazing

Dynamics of Lake Michigan Phytoplankton: Recent Changes in Surface and Deep Communities

Lake Michigan phytoplankton dynamics were studied from the end of spring isothermal mixing (May) through midstratification (July–August) in 1982–84. Phytoplankton composition shifted from a diatom-dominated community (75% of phytoplankton carbon) during May to a phytoflagellate-dominated community (71% of phytoplankton carbon) during July–August. This summer phytoflagellate dominance in the 1980s is distinctly different from the summer blue-green and green algae dominance in the 1970s. Foodweb interactions caused by a changing zooplankton composition and nutrient supply changes were two possible causes. A deep chlorophyll layer (DCL) developed after the onset of thermal stratification. The DCL initially developed in the 15–30 m region and deepended to 25–50 m in July and the 40–70 m region in August. The DCL in 1982–84 was larger in size and located deeper in the water column than those reported from the 1970s. This difference was related to increases in light transparency found in the 1980s that were a result of increased zooplankton grazing pressure.