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Food Webs (food + web)
Kinds of Food Webs Terms modified by Food Webs Selected AbstractsPopulation Density of the Crayfish, Orconectes limosus, in Relation to Fish and Macroinvertebrate Densities in a Small Mesotrophic Lake , Implications for the Lake's Food WebINTERNATIONAL REVIEW OF HYDROBIOLOGY, Issue 5-6 2005Susanne S. Haertel-Borer Abstract The population density of Orconectes limosus in a mesotrophic lake was assessed in the context of fish and macroinvertebrate biomasses, and crayfish consumption by fish. The average O.limosus (,6 cm total length) abundance and biomass in the littoral zone was 2200 ind ha,1 and 32.2 kg ha1, respectively. O.limosus biomass accounted for a large percentage (49%) of the lake's macroinvertebrate biomass. O.limosus was equal to 35% of the non-predatory fish biomass and to 81% of the predatory fish biomass. O.limosus comprised 15 and 48% of the annual consumption of pike and predatory perch, respectively. Altogether, O.limosus was identified as quantitatively important for the lake's littoral food web, and might also subsidize the pelagic food web. This strengthens the need for an integrated view on lake food webs. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Ultraviolet-B Radiation Effects on the Structure and Function of Lower Trophic Levels of the Marine Planktonic Food WebPHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 4 2006Gustavo A. Ferreyra ABSTRACT The impact of UV-B radiation (UVBR; 280,320 nm) on lower levels of a natural plankton assemblage (bacteria, phytoplankton and microzooplankton) from the St. Lawrence Estuary was studied during 9 days using several immersed outdoor mesocosms. Two exposure treatments were used in triplicate mesocosms: natural UVBR (N treatment, considered as the control treatment) and lamp-enhanced UVBR (H treatment, simulating 60% depletion of the ozone layer). A phytoplankton bloom developed after day 3, but no significant differences were found between treatments during the entire experiment for phytoplankton biomass (chlorophyll a and cell carbon) nor for phytoplankton cell abundances from flow cytometry and optical microscopy of three phytoplankton size classes (picoplankton, nanoplankton and microplankton). In contrast, bacterial abundances showed significantly higher values in the H treatment, attributed to a decrease in predation pressure due to a dramatic reduction in ciliate biomass (, 70,80%) in the H treatment relative to the N treatment. The most abundant ciliate species were Strombidinium sp., Prorodon ovum and Tintinnopsis sp.; all showed significantly lower abundances under the H treatment. P. ovum was the less-affected species (50% reduction in the H treatment compared with that of the N control), contrasting with ,90% for the other ones. Total specific phytoplanktonic and bacterial production were not affected by enhanced UVBR. However, both the ratio of primary to bacterial biomass and production decreased markedly under the H treatment. In contrast, the ratio of phytoplankton to bacterial plus ciliate carbon biomass showed an opposite trend than the previous results, with higher values in the H treatment at the end of the experiment. These results are explained by the changes in the ciliate biomass and suggest that UVBR can alter the structure of the lower levels of the planktonic community by selectively affecting key species. On the other hand, linearity between particulate organic carbon (POC) and estimated planktonic carbon was lost during the postbloom period in both treatments. On the basis of previous studies, our results can be attributed to the aggregation of carbon released by cells to the water column in the form of transparent exopolymer particles (TEPs) under nutrient limiting conditions. Unexpectedly, POC during such a period was higher in the H treatment than in controls. We hypothesize a decrease in the ingestion of TEPs by ciliates, in coincidence with increased DOC release by phytoplankton cells under enhanced UVBR. The consequences of such results for the carbon cycle in the ocean are discussed. [source] Effects of Human Exclusion on Parasitism in Intertidal Food Webs of Central ChileCONSERVATION BIOLOGY, Issue 1 2005GÉRALDINE LOOT Fissurella crassa; intermareal rocoso; parasitismo; Proctoeces lintoni; reservas marinas Abstract:,Numerous ecological studies have demonstrated the dramatic effects that humans have on coastal marine ecosystems. Consequently, marine reserves have been established to preserve biodiversity. Recent reviews show that this strategy has paid off because inside reserves, most species have rapidly increased in size and abundance. Even though these studies focused on free-living organisms and paid little attention to parasite populations, numerous authors support the hypothesis that parasitism levels could be good indicators of ecosystem stability. We examined harvesting effects on the dynamics of a parasitic trematode ( Proctoeces lintoni) that completes its life cycle in intertidal mussels ( Perumytilus purpuratus), keyhole limpets (Fissurella crassa), and clingfish ( Sicyases sanguineus). All of these species are directly or indirectly affected by humans. Prevalence and abundance of the trematode P. lintoni in the three host species were compared in four study sites that differed in the intensity of human harvest. Parasitism infection in limpets and mussels was significantly higher in areas protected from human harvesting than in open-access areas, which suggests a significant change in parasite dynamics inside reserves. Yet the average parasitic biomass found in the gonads of F. crassa did not differ between protected and open-access areas. These results show, then, that the parasite system responded by increasing infection rates in marine protected areas without implication for reproductive success of the intermediate host. Our findings show that the indirect effects of harvesting by humans on the embedded parasite communities of littoral ecosystems require further scientific investigation. Resumen:,Numerosos estudios ecológicos han demostrado los efectos dramáticos de la actividad humana sobre ecosistemas marinos costeros. Consecuentemente, se han establecido las reservas marinas para preservar la biodiversidad. Revisiones recientes muestran que esta estrategia es adecuada porque la mayoría de las especies dentro de las reservas han incrementado en tamaño y abundancia rápidamente. Aunque, estos estudios se han concentrado en organismos de vida libre y han puesto poca atención a poblaciones de parásitos, numerosos autores apoyan la hipótesis de que los niveles de parasitismo pueden ser buenos indicadores de la estabilidad del ecosistema. Examinamos los efectos de pesquería artesanal sobre la dinámica de un trematodo parásito ( Proctoeces lintoni) que completa su ciclo de vida en mitíldos intermareales ( Perumytilus purpuratus), lapas ( Fissurella crassa) y Sicyases sanguineus, los cuales son afectados por humanos directa o indirectamente. La prevalencia y abundancia del trematodo P. lintoni en las tres especies de hospedadores fueron comparadas en cuatro sitios de estudio que difieren en la intensidad de recolecta por humanos. La infección parasitaria en lapas y mitíldos fue significativamente mayor en áreas protegidas que en áreas de libre acceso, lo que sugiere un cambio significativo en la dinámica del parásito dentro de las reservas, pero, la biomasa promedio de parásitos en gónadas de F. crassa no fue diferente entre áreas protegidas y de libre acceso. Por lo tanto, los resultados muestran que el sistema parásito respondió incrementando tasas de infección en áreas marinas protegidas sin consecuencias sobre el éxito reproductivo del ho spedador intermediario. Nuestros hallazgos muestran que se requiere más investigación científica de los efectos indirectos de los humanos sobre las comunidades de parásitos en ecosistemas litorales. [source] Food Webs and Container Habitats: The Natural History and Ecology of PhytotelmataJOURNAL OF ECOLOGY, Issue 5 2001Article first published online: 26 MAR 200 No abstract is available for this article. [source] A Generic QSAR for Assessing the Bioaccumulation Potential of Organic Chemicals in Aquatic Food WebsMOLECULAR INFORMATICS, Issue 3 2003Abstract This study presents the development of a quantitative-structure activity relationship (QSAR) for assessing the bioaccumulation potential of organic chemicals in aquatic food webs. The QSAR is derived by parameterization and calibration of a mechanistic food web bioaccumulation model. Calibration of the QSAR is based on the derivation of a large database of bioconcentration and bioaccumulation factors, which is evaluated for data quality. The QSAR provides estimates of the bioaccumulation potential of organic chemicals in higher trophic level fish species of aquatic food webs. The QSAR can be adapted to include the effect of metabolic transformation and trophic dilution on the BAF. The BAF-QSAR can be applied to categorize organic chemical substances on their bioaccumulation potential. It identifies chemicals with a log KOW between 4.0 and 12.2 to exhibit BAFs greater than 5,000 in the absence of significant metabolic transformation rates. The BAF-QSAR can also be used in the derivation of water quality guidelines and total maximum daily loadings by relating internal concentrations of organic chemicals in upper trophic fish species to corresponding concentrations in the water. [source] The Protozooplankton,Ichthyoplankton Trophic Link: An Overlooked Aspect of Aquatic Food Webs,THE JOURNAL OF EUKARYOTIC MICROBIOLOGY, Issue 3 2010DAVID J. S. MONTAGNES ABSTRACT. Since the introduction of the microbial loop concept, awareness of the role played by protozooplankton in marine food webs has grown. By consuming bacteria, and then being consumed by metazooplankton, protozoa form a trophic link that channels dissolved organic material into the "classic" marine food chain. Beyond enhancing energy transfer to higher trophic levels, protozoa play a key role in improving the food quality of metazooplankton. Here, we consider a third role played by protozoa, but one that has received comparatively little attention: that as prey items for ichthyoplankton. For >100 years it has been known that fish larvae consume protozoa. Despite this, fisheries scientists and biological oceanographers still largely ignore protozoa when assessing the foodweb dynamics that regulate the growth and survival of larval fish. We review evidence supporting the importance of the protozooplankton,ichthyoplankton link, including examples from the amateur aquarium trade, the commercial aquaculture industry, and contemporary studies of larval fish. We then consider why this potentially important link continues to receive very little attention. We conclude by offering suggestions for quantifying the importance of the protozooplankton,ichthyoplankton trophic link, using both existing methods and new technologies. [source] Food webs in tropical Australian streams: shredders are not scarceFRESHWATER BIOLOGY, Issue 5 2005KIM CHESHIRE Summary 1. Macroinvertebrates were collected in dry and wet seasons from riffles and pools in two streams in tropical north Queensland. Total biomass, abundance and species richness were higher in riffles than in pools but did not differ between streams or seasons. 2. Gut contents of all species were identified. Cluster analysis based on gut contents identified five dietary groups: I, generalist collectors; II, generalist shredders and generalist predators; III, generalist scrapers; IV, specialist shredders; and V, specialist predators. Species were allocated to functional feeding groups (FFGs) based on these dietary groups. 3. Many species were generalist in their diets, but specialist predators and shredders were particularly prominent components of the invertebrate assemblages in terms of biomass and species richness. 4. Community composition (proportions of biomass, abundance and species richness of the different FFGs) varied between habitat types, but not between streams or seasons, although differences between riffles and pools varied with season. 5. Comparison of the fauna of 20 streams showed that our study sites were similar to, or not atypical of, low-order streams in the Queensland wet tropics. [source] Structural dynamics and robustness of food websECOLOGY LETTERS, Issue 7 2010Phillip P. A. Staniczenko Ecology Letters (2010) 13: 891,899 Abstract Food web structure plays an important role when determining robustness to cascading secondary extinctions. However, existing food web models do not take into account likely changes in trophic interactions (,rewiring') following species loss. We investigated structural dynamics in 12 empirically documented food webs by simulating primary species loss using three realistic removal criteria, and measured robustness in terms of subsequent secondary extinctions. In our model, novel trophic interactions can be established between predators and food items not previously consumed following the loss of competing predator species. By considering the increase in robustness conferred through rewiring, we identify a new category of species , overlap species , which promote robustness as shown by comparing simulations incorporating structural dynamics to those with static topologies. The fraction of overlap species in a food web is highly correlated with this increase in robustness; whereas species richness and connectance are uncorrelated with increased robustness. Our findings underline the importance of compensatory mechanisms that may buffer ecosystems against environmental change, and highlight the likely role of particular species that are expected to facilitate this buffering. [source] Bacterial traits, organism mass, and numerical abundance in the detrital soil food web of Dutch agricultural grasslandsECOLOGY LETTERS, Issue 1 2005Christian Mulder Abstract This paper compares responses to environmental stress of the ecophysiological traits of organisms in the detrital soil food webs of grasslands in the Netherlands, using the relationship between average body mass M and numerical abundance N. The microbial biomass and biodiversity of belowground fauna were measured in 110 grasslands on sand, 85 of them farmed under organic, conventional and intensive management. Bacterial cell volume and abundance and electrophoretic DNA bands as well as bacterial activity in the form of either metabolic quotient (qCO2) or microbial quotient (Cmic/Corg) predicted the response of microorganisms to stress. For soil fauna, the logarithm of body mass log(M) was approximately linearly related to the logarithm of numerical abundance log(N) with slope near ,1, and the regression slope and the proportion of predatory species were lower in intensive agroecosystems (more reduced substrates with higher energy content). Linear regression of log(N) on log(M) had slope not far from ,3/4. The approach to monitoring data illustrated in this paper could be useful in assessing land-use quality. [source] Parasites in the food web: linking amphibian malformations and aquatic eutrophicationECOLOGY LETTERS, Issue 7 2004Pieter T. J. Johnson Abstract Emerging diseases are an ever-growing affliction of both humans and wildlife. By exploring recent increases in amphibian malformations (e.g. extra or missing limbs), we illustrate the importance of food web theory and community ecology for understanding and controlling emerging infections. Evidence points to a native parasite, Ribeiroia ondatrae, as the primary culprit of these malformations, but reasons for the increase have remained conjectural. We suggest that the increase is a consequence of complex changes to aquatic food webs resulting from anthropogenic disturbance. Our results implicate cultural eutrophication as a driver of elevated parasitic infection: (1) eutrophication causes a predator-mediated shift in snail species composition toward Planorbella spp., (2) Planorbella are the exclusive first intermediate hosts of R. ondatrae and (3) Ribeiroia infection is a strong predictor of amphibian malformation levels. Our study illustrates how the effects of anthropogenic disturbance on epidemic disease can be mediated through direct and indirect changes in food web structure. [source] Top-down and bottom-up diversity cascades in detrital vs. living food websECOLOGY LETTERS, Issue 1 2003Lee A. Dyer Abstract Apex predators and plant resources are both critical for maintaining diversity in biotic communities, but the indirect (,cascading') effects of top-down and bottom-up forces on diversity at different trophic levels are not well resolved in terrestrial systems. Manipulations of predators or resources can cause direct changes of diversity at one trophic level, which in turn can affect diversity at other trophic levels. The indirect diversity effects of resource and consumer variation should be strongest in aquatic systems, moderate in terrestrial systems, and weakest in decomposer food webs. We measured effects of top predators and plant resources on the diversity of endophytic animals in an understorey shrub Piper cenocladum (Piperaceae). Predators and resource availability had significant direct and indirect effects on the diversity of the endophytic animal community, but the effects were not interactive, nor were they consistent between living vs. detrital food webs. The addition of fourth trophic level beetle predators increased diversity of consumers supported by living plant tissue, whereas balanced plant resources (light and nutrients) increased the diversity of primary through tertiary consumers in the detrital resources food web. These results support the hypotheses that top-down and bottom-up diversity cascades occur in terrestrial systems, and that diversity is affected by different factors in living vs. detrital food webs. [source] Food web complexity and chaotic population dynamicsECOLOGY LETTERS, Issue 3 2002Gregor F. Fussmann Abstract In mathematical models, very simple communities consisting of three or more species frequently display chaotic dynamics which implies that long-term predictions of the population trajectories in time are impossible. Communities in the wild tend to be more complex, but evidence for chaotic dynamics from such communities is scarce. We used supercomputing power to test the hypothesis that chaotic dynamics become less frequent in model ecosystems when their complexity increases. We determined the dynamical stability of a universe of mathematical, nonlinear food web models with varying degrees of organizational complexity. We found that the frequency of unpredictable, chaotic dynamics increases with the number of trophic levels in a food web but decreases with the degree of complexity. Our results suggest that natural food webs possess architectural properties that may intrinsically lower the likelihood of chaotic community dynamics. [source] Field evidence of trait-mediated indirect interactions in a rocky intertidal food webECOLOGY LETTERS, Issue 2 2002Geoffrey C. Trussell Studies on the implications of food web interactions to community structure have often focused on density-mediated interactions between predators and their prey. This approach emphasizes the importance of predator regulation of prey density via consumption (i.e. lethal effects), which, in turn, leads to cascading effects on the prey's resources. A more recent and contrasting view emphasizes the importance of non-lethal predator effects on prey traits (e.g. behaviour, morphology), or trait-mediated interactions. On rocky intertidal shores in New England, green crab (Carcinus maenas) predation is thought to be important to patterns of algal abundance and diversity by regulating the density of herbivorous snails (Littorina littorea). We found, however, that risk cues from green crabs can dramatically suppress snail grazing, with large effects on fucoid algal communities. Our results suggest that predator-induced changes in prey behaviour may be an important and under-appreciated component of food web interactions and community dynamics on rocky intertidal shores. [source] A methane-driven microbial food web in a wetland rice soilENVIRONMENTAL MICROBIOLOGY, Issue 12 2007Jun Murase Summary Methane oxidation is a key process controlling methane emission from anoxic habitats into the atmosphere. Methanotrophs, responsible for aerobic methane oxidation, do not only oxidize but also assimilate methane. Once assimilated, methane carbon may be utilized by other organisms. Here we report on a microbial food web in a rice field soil driven by methane. A thin layer of water-saturated rice field soil was incubated under opposing gradients of oxygen and 13C-labelled methane. Bacterial and eukaryotic communities incorporating methane carbon were analysed by RNA-stable isotope probing (SIP). Terminal restriction fragment length polymorphism (T-RFLP) and cloning showed that methanotrophs were the most prominent group of bacteria incorporating methane carbon. In addition, a few Myxobacteria -related sequences were obtained from the ,heavy' rRNA fraction. Denaturing gradient gel electrophoresis (DGGE) targeting 18S rRNA detected various groups of protists in the ,heavy' rRNA fraction including naked amoeba (Lobosea and Heterolobosea), ciliates (Colpodea) and flagellates (Cercozoa). Incubation of soil under different methane concentrations in air resulted in the development of distinct protozoan communities. These results suggest that methane carbon is incorporated into non-methanotrophic pro- and microeukaryotes probably via grazing, and that methane oxidation is a shaping force of the microeukaryotic community depending on methane availability. [source] Contaminant pattern and bioaccumulation of legacy and emerging organhalogen pollutants in the aquatic biota from an e-waste recycling region in South ChinaENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 4 2010Ying Zhang Abstract Legacy pollutants, polychlorinated biphenyls (PCBs), dichlorodiphenyl trichloroethane and its metabolites (DDTs), and some emerging organhalogen pollutants, such as polybrominated diphenyl ethers (PBDEs), hexabromobenzene (HBB), pentabromotoluene (PBT), 2,3,4,5,6-pentabromoethyl benzene (PBEB), 1,2- bis (2,4,6-tribromophenoxy) ethane (BTBPE), and dechlorane plus (DP), were detected in an aquatic food chain (invertebrates and fish) from an e-waste recycling region in South China. Polychlorinated biphenyls, DDTs, PBDEs, and HBB were detected in more than 90% of the samples, with respective concentrations ranging from not detected (ND),32,000,ng/g lipid weight, ND,850,ng/g lipid weight, 8 to 1,300,ng/g lipid weight, and 0.28 to 240,ng/g lipid weight. Pentabromotoluene, PBEB, BTBPE, and DP were also quantifiable in collected samples with a concentration range of ND,40,ng/g lipid weight. The elevated levels of PCBs and PBDEs in the organisms, compared with those in non-e-waste regions in South China, suggest that these two kinds of pollutants derived mainly from e-waste recycling practices. Hexabromobenzene was significantly correlated with PBDEs, implying that HBB come from the release of e-waste along with PBDEs and/or the pyrolysis of BDE209. Most of the compounds whose trophic magnification factor (TMF) could be calculated were found to biomagnify (TMF > 1). Hexabromobenzene was also found, for the first time, to biomagnify in the present food web, with a TMF of 2.1. Environ. Toxicol. Chem. 2010;29:852,859. © 2010 SETAC [source] Chemical amplification in an invaded food web: Seasonality and ontogeny in a high-biomass, low-diversity ecosystem,ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 10 2008Carla A. Ng Abstract The global spread of invasive species is changing the structure of aquatic food webs worldwide. The North American Great Lakes have proved particularly vulnerable to this threat. In nearshore areas, invasive benthic species such as dreissenid mussels and round gobies (Neogobius melanostomus) have gained dominance in recent years. Such species are driving the flow of energy and material from the water column to the benthic zone, with dramatic effect on nutrient and contaminant cycling. Here, we develop a stage-structured model of a benthified food web in Lake Michigan with seasonal resolution and show how its bioaccumulation patterns differ from expected ones. Our model suggests that contaminant recycling through the consumption of lipid-rich fish eggs and mussel detritus is responsible for these differences. In southern Lake Michigan's Calumet Harbor (Chicago, IL, USA), round gobies have nitrogen isotope signatures with considerable spread, with some values higher than their predators and others lower than their prey. Contrary to patterns observed in linear pelagic systems, we predict that polychlorinated biphenyl (PCB) concentrations in these fish decrease with increasing size due to the lipid- and benthos-enriched diets of smaller fish. We also present here round goby PCB concentrations measured in 2005 after an invasional succession in Calumet Harbor and demonstrate how the change from one invasive mussel species to another may have led to a decrease in round goby PCB accumulation. Our results suggest that benthic-dominated systems differ from pelagic ones chiefly due to the influence of detritus and that these effects are exacerbated in systems with low species diversity and high biomass. [source] Examining the single and interactive effects of three insecticides on amphibian metamorphosis,ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 7 2008Michelle D. Boone Abstract Although aquatic communities frequently are exposed to a number of pesticides, the effects of chemical mixtures are not well understood. In two separate studies, I examined how insecticide mixtures influenced the likelihood of unpredictable, nonadditive effects on American toad (Bufo americanus) and green frog (Rana clamitans) tadpoles reared in outdoor aquatic communities. I exposed tadpoles to single or multiple insecticides at approximately half the reported median lethal concentrations using insecticides that were either acetylcholinesterase inhibitors (carbaryl or malathion) or a sodium-channel disruptor (permethrin). I found that combinations of insecticides with the same mode of action were more likely to have nonadditive effects on amphibian metamorphosis compared with those having different modes of action. Additionally, in one study, a commercial formulation of permethrin led to near-complete elimination of American toads, suggesting that this formulation could have adverse effects on aquatic communities. Many community studies exploring the ecological effects of expected environmental concentrations of pesticides have suggested that indirect effects in the food web, rather than direct effects on individual physiology, have the largest effect on amphibians. The present study indicates that direct effects of pesticides may become particularly important when insecticides with the same mode of action are present in the environment. [source] Tracing salmon-derived nutrients and contaminants in freshwater food webs across a pronounced spawner density gradientENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 6 2007Irene Gregory-Eaves Abstract Many have demonstrated that anadromous Pacific salmon are significant vectors of nutrients from the ocean to freshwaters. Recently, however, it has been recognized that salmon spawners also input significant quantities of contaminants. The objectives of this paper are to delineate the extent to which salmon-derived nutrients are integrated into the freshwater food web using ,15N and ,13C and to assess the influence of the salmon pathway in the accumulation of contaminants in rainbow trout (Oncorhynchus mykiss). We found that the ,15N and ,13C of food web components were related positively and significantly to sockeye salmon (Oncorhynchus nerka) spawner density. Contaminant concentrations in rainbow trout also positively and significantly were related to sockeye salmon spawner density. These data suggest that the anadromous salmon nutrient and contaminant pathways are related and significantly impact the contaminant burden of resident fish. [source] Wading birds as bioindicators of mercury contamination in Florida, USA: Annual and geographic variationENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 1 2002Peter C. Frederick Abstract Mercury contamination in wetland biota is often dynamic, difficult to predict, and costly to track. In this paper, we present results from a six-year study of growing feathers of piscivorous birds as monitors of wetland Hg exposure in Florida, USA, wetlands. Between 1994 and 2000, we collected feathers of growing great egret (Ardea alba) nestlings from colonies in the freshwater Everglades of southern Florida, and during 1998, feathers were collected from chicks of both great egrets and white ibises (Eudocimus albus) at a variety of colonies throughout peninsular Florida. Coastal colonies showed significantly lower feather Hg concentrations than did inland sites. Within the Everglades, we found significant effects of both geographic location and year on age-adjusted mean total Hg concentrations in feathers. Over the course of our study, Everglades colonies maintained their Hg concentration rankings relative to one another, but all showed strongly declining Hg concentrations (mean of 73% averaged across colonies, between 1994 and 2000). Using a previously established predictive relationship between Hg consumption in food and feather Hg for great egrets, we estimated that Hg concentrations in the aggregate diet of egrets have been reduced by an average of 67%. We conclude that the Everglades has undergone a biologically significant decline in Hg availability in the wetland food web, possibly because of decreased local inputs. [source] Methane assimilation and trophic interactions with marine Methylomicrobium in deep-water coral reef sediment off the coast of NorwayFEMS MICROBIOLOGY ECOLOGY, Issue 2 2008Sigmund Jensen Abstract Deep-water coral reefs are seafloor environments with diverse biological communities surrounded by cold permanent darkness. Sources of energy and carbon for the nourishment of these reefs are presently unclear. We investigated one aspect of the food web using DNA stable-isotope probing (DNA-SIP). Sediment from beneath a Lophelia pertusa reef off the coast of Norway was incubated until assimilation of 5 ,mol 13CH4 g,1 wet weight occurred. Extracted DNA was separated into ,light' and ,heavy' fractions for analysis of labelling. Bacterial community fingerprinting of PCR-amplified 16S rRNA gene fragments revealed two predominant 13C-specific bands. Sequencing of these bands indicated that carbon from 13CH4 had been assimilated by a Methylomicrobium and an uncultivated member of the Gammaproteobacteria. Cloning and sequencing of 16S rRNA genes from the heavy DNA, in addition to genes encoding particulate methane monooxygenase and methanol dehydrogenase, all linked Methylomicrobium with methane metabolism. Putative cross-feeders were affiliated with Methylophaga (Gammaproteobacteria), Hyphomicrobium (Alphaproteobacteria) and previously unrecognized methylotrophs of the Gammaproteobacteria, Alphaproteobacteria, Deferribacteres and Bacteroidetes. This first marine methane SIP study provides evidence for the presence of methylotrophs that participate in sediment food webs associated with deep-water coral reefs. [source] Lead and cadmium uptake in the marine fungi Corollospora lacera and Monodictys pelagicaFEMS MICROBIOLOGY ECOLOGY, Issue 3 2005Michael A.S. Taboski Abstract This study provides observations on the effects of lead and cadmium ions on the growth of two species of marine fungi, Corollospora lacera and Monodictys pelagica. On solid media lead appeared to have no effect on the radial rate of growth of fungi. Exposure to increasing cadmium concentrations on solid media resulted in significant reduction (P < 0.05) in the radial mycelial growth rates of both fungi, especially in M. pelagica. These results reveal significant difference in species sensitivity toward cadmium and, essentially, insensitivity toward lead exposure. In liquid cultures, the metal content of mycelia (metal mass found in mycelium, in mg), and the concentration of metal in dry mycelium (metal mass in 1 g of mycelium, in mg g,1) were both found to increase (P < 0.05) with the increase in the metal cation concentration, while mycelium dry mass decreased. As it was observed on solid media, cadmium cation affected more severely (P < 0.05) the growth of M. pelagica in liquid cultures. Ergosterol content of mycelia of C. lacera exposed to increasing cadmium cation concentration decreased, similarly to the trend observed for dry mycelial mass. It was found that ca. 93% of all lead sequestered by C. lacera is located extracellularly. M. pelagica was found to bioaccumulate over 60 mg of cadmium and over 6 mg of lead per 1 g of mycelium, while C. lacera bioaccumulated over 7 mg of cadmium and up to 250 mg of lead per 1 g of mycelium. Overall, the results indicate that both metal ions affect the growth of marine fungi with lead being accumulated extracellularly in the mycelia. Both metals accumulated by fungi may then enter the marine ecosystem food web, of which marine fungi are integral members. [source] How well are velocity effects on ,13C signatures transmitted up the food web from algae to fish?FRESHWATER BIOLOGY, Issue 6 2010JOSEPH B. RASMUSSEN Summary 1. Benthic algae fractionate carbon isotopes less at low water velocities because of reduced boundary layer exchange, and this effect on ,13C is passed on to consumers via trophic transfer. This study examines the relationships between ,13C signatures of consumers (invertebrates and salmonid fishes) and water velocity in the Sainte Marguerite River, QC, Canada, and compares them to patterns for periphyton, both along the river main-stem and in a small tributary. 2. Relationships of ,13C signatures of herbivore/grazers and collector/gatherers with water velocity were strong and similar to those of periphyton, but relationships for filter-feeders were weak, probably reflecting the effect of spatial averaging of their food supply as a result of downstream transport. 3. Velocity effects on salmonid signatures were much weaker than those of lower trophic levels, being barely significant except in the small tributary where the fish were resident and isolated from the main river. In the river main-stem, even when reach standardised (reach mean subtracted from each data point), fish signatures were only weakly related to water velocity. 4. The fidelity with which velocity effects are transmitted to consumers from benthic algae is highly variable, and depends on a combination of consumer and resource movements, in addition to the trophic position of the consumer. [source] Impact of the fish Garra on the ecology of reservoirs and the occurrence of Microcystis blooms in semi-arid tropical highlands: an experimental assessment using enclosuresFRESHWATER BIOLOGY, Issue 8 2009TADESSE DEJENIE Summary 1.,Many man-made reservoirs in the semi-arid highlands of Northern Ethiopia (Tigray) are characterised by the occurrence of intensive blooms of cyanobacteria and a dominance of small riverine fishes belonging to the genus Garra. 2.,We carried out enclosure experiments to test for the effect of these small fish on abiotic characteristics, phytoplankton biomass and zooplankton community structure in the pelagic of two reservoirs (Gereb Awso and Tsinkanet). Two experiments were carried out in each of the reservoirs, one at the end of the rainy season (highest water level) and one at the end of the dry season (lowest water level). 3.,The presence of Garra in general increased the amount of suspended matter, nutrient concentrations (total nitrogen and total phosphorus), phytoplankton and Microcystis biomass (including the proportion of Microcystis in the phytoplankton community), and reduced water transparency. The positive effect of the presence of Garra on nutrient concentrations and phytoplankton productivity indicate that Garra has the potential to affect food web functioning indirectly through bottom-up effects, by enhancing nutrient concentrations through sediment resuspension and excretion of nutrients. Indeed, population densities of the cladoceran zooplankton taxa Ceriodaphnia and Diaphanosoma also showed an overall increase in enclosures with Garra. 4.,However, our data also provide some evidence for a potential of Garra to exert top-down control on large bodied daphnids (Daphnia carinata, D. barbata), although such effect varied among experiments. The limited capability of Garra to control zooplankton communities mainly reflects the low efficiency of these small, riverine and benthos-oriented fish in foraging on zooplankton and suggests the existence of an unoccupied niche for zooplanktivorous fish in the majority of the reservoirs. 5.,Although the main effects of Garra on the pelagic food web seemed to be mediated by bottom-up mechanisms, our results also indicate that one of the key variables, the relative abundance of Microcystis, was impacted by Daphnia -mediated trophic cascade effects. [source] Feeding rates, assimilation efficiencies and growth of two amphipod species on biodeposited material from zebra musselsFRESHWATER BIOLOGY, Issue 12 2008RENÉ GERGS Summary 1. Accumulation of organic material by the zebra mussel Dreissena polymorpha is assumed to be the source of a biodeposition-based food web. However, only little is known about the importance of the biodeposited material as a food source and its contribution to increased abundances of macroinvertebrates in the presence of D. polymorpha. 2. Feeding, assimilation and growth of the amphipods Gammarus roeselii and Dikerogammarus villosus on food sources directly and indirectly associated with D. polymorpha (biodeposited material and chironomids) and on conditioned alder leaves were measured. The stoichiometry of carbon, nitrogen and phosphorus of the diets was measured as an important determining factor of food quality. 3. Chironomids had the highest nitrogen and phosphorus contents, alder leaves were depleted in nitrogen and phosphorus, and the stoichiometry of biodeposited material was intermediate. 4. Both amphipod species had highest feeding rates and assimilation efficiencies on chironomids. Gammarus roeselii fed more on biodeposited material than on alder leaves, but assimilation efficiencies were similar; D. villosus also had similar feeding rates and assimilation efficiencies on the two diets. 5. Both amphipod species had highest growth rates on chironomids and lowest growth rates on alder leaves. Both grew at intermediate rates on biodeposited material of D. polymorpha. The growth rates of the amphipod species were related to food stoichiometry. Overall, the invasive D. villosus grew faster than the indigenous G. roeselii. 6. Food resources directly and indirectly associated with D. polymorpha are potential diets for amphipods, providing further evidence for a D. polymorpha biodeposition-based food web. [source] Hydrologic versus geomorphic limitation on CPOM storage in stream ecosystemsFRESHWATER BIOLOGY, Issue 8 2008MELANIE J. SMALL Summary 1. Stream ecosystems are the products of interactions between hydrology, geomorphology and ecology, but examining all three components simultaneously is difficult and rarely attempted. Frequently, either geomorphology or hydrology is treated as invariable or static. 2. To examine the validity of treating either hydrology or geomorphology as static, we studied the individual and combined effects of hydrology and channel geomorphology on coarse particulate organic matter (CPOM) storage. Using data from an experimental leaf release in a hydrologically regulated stream we created a simple numerical model. This allowed us to quantify the relative influence of CPOM trapping and CPOM retention on total long-term CPOM storage under variable regimes of flood frequency and geomorphic structure. 3. CPOM storage is a function of supply, flood frequency and the type and frequency of in-stream structures. In-stream structures perform two distinct functions, trapping and retention, whose relative importance in leaf storage changes with stream hydrology. Trapping is more important for CPOM storage in streams with few floods, while retention is more important in streams with frequent floods. Different structures (e.g. boulders, large wood, small wood) perform these functions at different efficiencies. We found that large wood trapped two to three times more leaves than the bank, but that the bank retained leaves two to three times more efficiently. 4. A modelled channel with five times the amount of large wood as the study channel (a ,wood restoration') initially stored 14% more leaves than the modelled ,natural' channel. After six floods, however, the modelled wood restoration channel stored 50% less CPOM than the natural channel as the large wood had high trapping but poor retention. The modelled natural channel contained structures that could both trap and retain. Thus, as different structures performed different functions, the structural complexity buffered the stream allochthonous energy base against changes in hydrology through its balance of trapping and retention. 5. As the frequency of floods increased, the spatial distribution of CPOM became increasingly patchy as storage was driven entirely by structures with high retention. Thus, the coupling of flood frequency and geomorphic structure influenced CPOM availability, which in turn has ramifications for the entire stream food web. [source] Effects of drying regime on microbial colonization and shredder preference in seasonal woodland wetlandsFRESHWATER BIOLOGY, Issue 3 2008MARTYN D. INKLEY Summary 1. Energy budgets of wetlands in temperate deciduous forests are dominated by terrestrially derived leaf litter that decays under different drying conditions depending on autumn precipitation. We compared decay rates and microbial colonization of maple leaves under different inundation schedules in a field experiment, and then conducted a laboratory study on shredder preference. In the field, litter bags either remained submerged (permanent), were moved to a dried part of the basin once and then returned (semi-permanent), or were alternated between wet and dry conditions for 8 weeks (temporary). 2. There was no difference in decay rates among treatments, but leaves incubated under permanent and semi-permanent conditions had higher fungal and bacterial biomass, and lower C : N ratios than those incubated under alternating drying and wetting conditions. 3. To determine the effects of these differences in litter nutritional quality on shredder preference, we conducted a laboratory preference test with larvae of leaf-shredding caddisflies that inhabit the wetland. Caddisflies spent twice as much time foraging on permanent and semi-permanent litter than on litter incubated under temporary conditions. 4. There is considerable variation among previous studies in how basin drying affects litter breakdown in wetlands, and no previous information on shredder preference. We found that frequent drying in a shallow wetland reduces the nutritional quality of leaf litter (lower microbial biomass and nitrogen content), and therefore preference by invertebrate shredders. These results suggest that inter-annual shifts in drying regime should alter detritus processing rates, and hence the mobilization of the energy and nutrients in leaf litter to the wetland food web. [source] The significance of side-arm connectivity for carbon dynamics of the River Danube, AustriaFRESHWATER BIOLOGY, Issue 2 2008S. PREINER Summary 1. Side-arms connected to the main stem of the river are key areas for biogeochemical cycling in fluvial landscapes, exhibiting high rates of carbon processing. 2. This work focused on quantifying autochthonous and allochthonous carbon pools and, thereby, on comparing transport and transformation processes in a restored side-arm system of the River Danube (Regelsbrunn). We established a carbon budget and quantified carbon processing from March to September 2003. In addition, data from previous studies during 1997 to 1999 were assessed. 3. Gross primary production (GPP) and community respiration were estimated by diel oxygen time curves and an oxygen mass balance. Plankton primary production was determined to estimate its contribution to GPP under different hydrological conditions. 4. Based on the degree of connectivity, three hydrological phases were differentiated. Most of the organic matter, dominated by allochthonous carbon, was transported in the main channel and through the side-arm during floods, while at intermediate and low flows (and thus connectivity), transformation processes became more important and autochthonous carbon dominated the carbon pool. The side-arm system functioned as a sink for particulate matter [total suspended solids and particulate organic carbon (POC)] and a source of dissolved organic carbon (DOC) and chlorophyll- a. 5. Autochthonous primary production of 4.2 t C day,1 in the side-arm was equivalent to about 20% of the allochthonous inputs of 20 t C day,1 (POC and DOC) entering the area at mean flow (1% of the discharge of the main channel). Pelagic photosynthesis was generally high at mean flow (1.3,3.8 g C m,2 day,1), and contributed up to 90% of system productivity. During long stagnant periods at low discharge, the side-arm was controlled by biological processes and a shift from planktonic to benthic activity occurred (benthic primary production of 0.4,14 g C m,2 day,1). 6. The transformation of the organic matter that passes through the side-arm under different hydrological conditions, points to the importance of these subsystems in contributing autochthonous carbon to the food web of the main channel. [source] Temporal dynamics and growth of Actinophrys sol (Sarcodina: Heliozoa), the top predator in an extremely acidic lakeFRESHWATER BIOLOGY, Issue 6 2006ELANOR M. BELL Summary 1. The in situ abundance, biomass and mean cell volume of Actinophrys sol (Sarcodina: Heliozoa), the top predator in an extremely acidic German mining lake (Lake 111; pH 2.65), were determined over three consecutive years (spring to autumn, 2001,03). 2. Actinophrys sol exhibited pronounced temporal and vertical patterns in abundance, biomass and mean cell volume. Increasing from very low spring densities, maxima in abundance and biomass were observed in late June/early July and September. The highest mean abundance recorded during the study was 7 × 103 Heliozoa L,1. Heliozoan abundance and biomass were higher in the epilimnion than in the hypolimnion. Actinophrys sol cells from this acidic lake were smaller than individuals of the same species found in other aquatic systems. 3. We determined the growth rate of A. sol using all potential prey items available in, and isolated and cultured from, Lake 111. Prey items included: single-celled and filamentous bacteria of unknown taxonomic affinity, the mixotrophic flagellates Chlamydomonas acidophila and Ochromonas sp., the ciliate Oxytricha sp. and the rotifers Elosa worallii and Cephalodella hoodi. Actinophrys sol fed over a wide-size spectrum from bacteria to metazoans. Positive growth was not supported by all naturally available prey. Actinophrys sol neither increased in cell number (k) nor biomass (kb) when starved, with low concentrations of single-celled bacteria or with the alga Ochromonas sp. Positive growth was achieved with single-celled bacteria (k = 0.22 ± 0.02 d,1; kb = ,0.06 ± 0.02 d,1) and filamentous bacteria (k = 0.52 ± <0.01 d,1; kb = 0.66 d,1) at concentrations greater than observed in situ, and the alga C. acidophila (up to k = 0.43 ± 0.03 d,1; kb = 0.44 ± 0.04 d,1), the ciliate Oxytricha sp. (k = 0.34 ± 0.01 d,1) and in mixed cultures containing rotifers and C. acidophila (k = 0.23 ± 0.02,0.32 ± 0.02 d,1; maximum kb = 0.42 ± 0.05 d,1). The individual- and biomass-based growth of A. sol was highest when filamentous bacteria were provided. 4. Existing quantitative carbon flux models for the Lake 111 food web can be updated in light of our results. Actinophrys sol are omnivorous predators supported by a mixed diet of filamentous bacteria and C. acidophila in the epilimnion. Heliozoa are important components in the planktonic food webs of ,extreme' environments. [source] Water temperature determines strength of top-down control in a stream food webFRESHWATER BIOLOGY, Issue 8 2005DAISUKE KISHI Summary 1. We examined effects of water temperature on the community structure of a three trophic level food chain (predatory fish, herbivorous caddisfly larvae and periphyton) in boreal streams. We used laboratory experiments to examine (i) the effects of water temperature on feeding activities of fish and caddisfly larvae and on periphyton productivity, to evaluate the thermal effects on each trophic level (species-level experiment), and (ii) the effects of water temperature on predation pressure of fish on abundance of the lower trophic levels, to evaluate how temperature affects top-down control by fish (community-level experiment). 2. In the species-level experiment, feeding activity of fish was high at 12 °C, which coincides with the mean summer temperature in forested streams of Hokkaido, Japan, but was depressed at 3 °C, which coincides with the mean winter temperature, and also above 18 °C, which coincides with the near maximum summer temperatures. Periphyton productivity increased over the range of water temperatures. 3. In the community-level experiments, a top-down effect of fish on the abundance of caddisfly larvae and periphyton was clear at 12 °C. This effect was not observed at 3 and 21 °C because of low predation pressure of fish at these temperatures. 4. These experiments revealed that trophic cascading effects may vary with temperature even in the presence of abundant predators. Physiological depression of predators because of thermal stress can alter top-down control and lead to changes in community structure. 5. We suggest that thermal habitat alteration can change food web structure via combinations of direct and indirect trophic interactions. [source] Effect of temperature on development and growth of the raptorial cladoceran Leptodora kindtii under laboratory conditionsFRESHWATER BIOLOGY, Issue 11 2004Jacobus Vijverberg Summary 1. Leptodora is a key species in many temperate freshwater systems, but so far its role in the food web could not be properly evaluated because detailed information about its secondary production was lacking. As we wanted to estimate the secondary production of Leptodora, we measured its development and growth rates in the laboratory. 2. Employing improved methods to estimate growth and instar durations, we cultured Leptodora kindtii in the laboratory at four constant temperatures (15, 17.5, 20 and 25 °C). Growth in length and development times of eggs and instar stages were assessed. 3. Growth rates at 15, 17.5 and 20 °C were similar, but at 25 °C growth was distinctly faster. At 17.5 °C we observed seven juvenile instar stages before the first adult instar stage was reached. [source] | |||||||||||||||||||||||||||||||||||||