Long‐term variation in the littoral food web of an acidified mountain lake

Evidence of chemical recovery from acidification in European freshwaters has emerged in recent years, with many previously damaged systems responding to decades of reduced acidifying emissions. Biological recovery, however, has often lagged behind, and this has been ascribed to several possible mechanisms, including inertia in the food web. We examined two decades of change in hindcasted food webs for Lochnagar, a Scottish mountain lake, to make inferences about the potential dynamical stability of the system and to assess the prospects for future biological recovery. Although community composition tracked temporal changes in acidity, this was neither sustained nor directional, and mainly manifested as shifts in relative abundances rather than the establishment of more acid‐sensitive species. The food web was highly interconnected and reticulate, especially in years when species richness was low, and subsidized by external inputs of detritus. Among the primary consumers, generalist herbivore–detritivores maintained feeding links with the scant algal resources, which appeared insufficient to support viable populations of specialist grazers. Together, these characteristics, which are shared with many other acidified freshwaters, are likely to make the community dynamically stable and resistant to invasions of potential new colonists, thereby slowing the pace of future biological recovery.     

Long‐term increases in intrinsic water‐use efficiency do not lead to increased stem growth in a tropical monsoon forest in western Thailand

Rising atmospheric carbon dioxide [CO₂] can accelerate tree growth by stimulating photosynthesis and increasing intrinsic water‐use efficiency (iWUE). Little evidence exists, however, for the long‐term growth and gas‐exchange responses of mature trees in tropical forests to the combined effects of rising [CO₂] and other global changes such as warming. Using tree rings and stable isotopes of carbon and oxygen, we investigated long‐term trends in the iWUE and stem growth (basal area increment, BAI) of three canopy tree species in a tropical monsoon forest in western Thailand (Chukrasia tabularis, Melia azedarach, and Toona ciliata). To do this, we modelled the contribution of ontogenetic effects (tree diameter or age) and calendar year to variation in iWUE, oxygen isotopes, and BAI using mixed‐effects models. Although iWUE increased significantly with both tree diameter and calendar year in all species, BAI at a given tree diameter was lower in more recent years. For one species, C. tabularis, differences in crown dominance significantly influence stable isotopes and growth. Tree ring Δ¹⁸O increased with calendar year in all species, suggesting that increasing iWUE may have been driven by relatively greater reductions in stomatal conductance – leading to enrichment in Δ¹⁸O – than increases in photosynthetic capacity. Plausible explanations for the observed declines in growth include water stress resulting from rising temperatures and El Niño events, increased respiration, changes in allocation, or more likely, a combination of these factors.     

Effects of an invasive crayfish on trophic relationships in north‐temperate lake food webs

1. The introduction of invasive species is one of the main threats to global biodiversity, ecosystem structure and ecosystem processes. In freshwaters, invasive crayfish alter macroinvertebrate community structure and destroy macrophyte beds. There is limited knowledge on how such invasive species‐driven changes affect consumers at higher trophic levels. 2. In this study, we explore how the invasive rusty crayfish Orconectes rusticus, a benthic omnivore, affects benthic macroinvertebrates, as well as the broader consequences for ecosystem‐level trophic flows in terms of fish benthivory and trophic position (TP). We expected crayfish to decrease abundance of benthic macroinvertebrates, making most fish species less reliant on benthic resources. We expected crayfish specialists (e.g. Lepomis sp. and Micropterus sp.) to increase their benthic dependence. 3. In 10 northern Wisconsin lakes, we measured rusty crayfish relative abundance (catch per unit effort, CPUE), macroinvertebrate abundance, and C and N stable isotope ratios of 11 littoral fish species. We used stable isotope data and mixing models to characterise the trophic pathways supporting each fish species, and related trophic structure to crayfish relative abundance, fish body size and abiotic predictors using hierarchical Bayesian models. 4. Benthic invertebrate abundance was negatively correlated with rusty crayfish relative abundance. Fish benthivory increased with crayfish CPUE for all 11 fish species; posterior probabilities of a positive effect were >95%. TP also increased slightly with crayfish CPUE for some species, particularly smallmouth bass, largemouth bass, rock bass and Johnny darter. Moreover, both fish body size and lake abiotic variables explained variation in TP, while their effects on benthivory were small. 5. Rusty crayfish abundance explained relatively little of the overall variation in fish benthivory and TP. Although rusty crayfish appear to have strong effects on abundances of benthic macroinvertebrates, energy flow pathways and trophic niches of lentic fishes were not strongly influenced by invasive rusty crayfish.     

Long‐term dynamics of submerged macrophytes and algae in a small and shallow,eutrophic lake: implications for the stability of macrophyte‐dominance

1. Submerged macrophyte and phytoplankton components of eutrophic, shallow lakes have frequently undergone dynamic changes in composition and abundance with important consequences for lake functioning and stability. However, because of a paucity of long‐term survey data, we know little regarding the nature, direction and sequencing of such changes over decadal–centennial or longer timescales. 2. To circumvent this problem, we analysed multiple (n = 5) chronologically correlated sediment cores for plant macro‐remains and a single core for pollen and diatoms from one small, shallow, English lake (Felbrigg Hall Lake, Norfolk, U.K.), documenting 250 years of change to macrophyte and algal communities. 3. All five cores showed broadly similar stratigraphic changes in macrophyte remains with three distinct phases of macrophyte development: Myriophyllum–Chara–Potamogeton (c. pre‐1900), to Ceratophyllum–Chara–Potamogeton (c. 1900–1960) and finally to Zannichellia–Potamogeton (c. post‐1960). Macrophyte species richness declined from at least 10 species pre‐1900 to just four species at the present day. Additionally, in the final Zannichellia–Potamogeton phase, a directional shift between epi‐benthic and phytoplankton‐based primary production was indicated by the diatom data. 4. Based on macrophyte–seasonality relationships established for the region, concomitant with the final shift to Zannichellia–Potamogeton, we infer a reduction in the seasonal duration of plant dominance (plant‐covered period). Furthermore, we hypothesise that this change in species composition resulted in a situation whereby macrophyte populations were seasonally ‘sandwiched’ between two phytoplankton peaks in spring and late summer as observed in the contemporary lake. 5. We suggest that eutrophication‐induced reductions in macrophyte species richness, especially if the number of plant‐seasonal strategies is reduced, may constrict the plant growing season. In turn, this may render a shallow lake increasingly vulnerable to seasonal invasions of phytoplankton resulting in further species losses in the plant community. Thus, as part of a slow (over perhaps 10–100s of years) and self‐perpetuating process, macrophytes may be gradually pushed out by phytoplankton without the need for a perturbation as required in the alternative stable states model of plant loss.     

Ten polymorphic microsatellite markers in the invasive round goby (Neogobius melanostomus) and cross‐species amplification

Ten tetranucleotide, dinucleotide and compound microsatellite loci were isolated and characterized for the round goby, Neogobius melanostomus. Analysis of 64 gobies from one nonindigenous population in Lake Erie, Ontario, Canada, indicated that allele number varied from three to 12 per locus, while observed heterozygosity ranged between 0.33 and 0.86. Eight of these primers showed some amplification in other species in four genera. These newly developed microsatellite markers are a powerful tool that will provide insights into population structure and dispersal of the round goby in their novel environment.     

Long‐term phytoplankton community changes in a deep subalpine lake: responses to nutrient availability and climatic fluctuations

1. In natural lakes, modifications in the species composition and abundance of phytoplankton communities may ultimately be responses to changes in nutrient availability and climatic fluctuations. Phytoplankton and associated environmental factors were collected at monthly intervals from the beginning of the 1990s to 2007 in the large subalpine Lake Garda (z_max = 350 m, V = 49 × 10⁹ m³). In this study period, the lake showed a slight and continuous increase of total phosphorus (TP) in the water column, up to concentrations of 18–20 μg P L^?1. This increase represented the last stage of a long‐term process of enrichment documented since the 1970s, when concentrations of TP were below or around 10 μg P L^?1. 2. At the community level, annual phytoplankton cycles underwent a unidirectional and slow shift mainly due to changes in the species more affected by the nutrient enrichment of the lake. After a first and long period of dominance by conjugatophytes (Mougeotia) and diatoms (Fragilaria), phytoplankton biomass in recent years was sustained by cyanobacteria (Planktothrix). Other important modifications in the development of phytoplankton were superimposed on this pattern due to the effects of annual climate fluctuations principally mediated by the deep mixing events at spring overturn and, secondarily, by temperature and thermal stability of the water column during the growing season. 3. Interannual variations in the stability and temperature of the water column appeared to influence the development of a few subdominant flagellates (dinophytes and cryptophytes). Nevertheless, the major impact of climate on phytoplankton was indirect, and mediated through the effects of winter climatic conditions on deep mixing dynamics. Winter climatic fluctuations proved to be a key element in a linked chain of causal factors including cooling of hypolimnetic waters, deep vertical mixing and epilimnetic nutrient replenishment. The process of fertilisation was measurable both for TP and dissolved inorganic nitrogen, although only the first had a large effect, reinforcing the seasonal growth of a few dominant groups. The degree of nutrient replenishment further increased the spring development of large diatoms and the increase of Planktothrix in summer and autumn. 4. Currently, changes in nutrient concentrations have the greatest effect on the phytoplankton community, while direct effects due to the interannual variations in the thermal regime are of secondary importance compared with the indirect effects mediated through deep water mixing and spring fertilisation. Overall, the results demonstrate that the consequences of climatic fluctuations and climate warming on phytoplankton communities need to be studied at different levels of complexity and integration, from the direct effects of temperature and thermal regime, to the indirect effects mediated by the physiographic characteristics of water bodies.     

Plankton metabolism and physical forcing in a productive embayment of a large oligotrophic lake: insights from stable oxygen isotopes

1. The metabolic balance of plankton communities, commonly assessed by the photosynthesis‐to‐respiration ratio (P : R), has received much attention recently in connection with allochthonous organic subsidies to lakes, while the role of physical, climate‐related forces has received less attention. 2. Here we evaluated the effects of wind and upwelling events on plankton metabolism and the potential of stable oxygen isotopes to characterise P, R and P : R on the scales necessary to characterise properly physical forcing effects in large lakes. 3. We measured the ¹⁸O/¹⁶O ratio of dissolved oxygen and water in a large productive embayment of Lake Ontario (Hamilton Harbour, Canada) and estimated P, R and P : R from the steady state solutions of a widely accepted mass balance model, together with estimates of wind‐driven gas exchange, and compared the results with those from experimental incubations of plankton samples. 4. Estimates of P, but not R, from the isotope model were significantly correlated with bottle estimates while average P : R was similar by both methods. Closer examination of physical forcing events led to a model of how wind events induce mixing, upwelling, exchange and consequent changes in P and R. These physical forcing events were captured more by the isotope model than by the bottle estimates, as episodes of immediately increased R and decreased P : R, with a subsequent stimulation of P. 5. The oxygen isotope approach provided valuable measures of plankton metabolism and helped to characterise more effectively the substantial effects on P : R of physical forcing and, in particular, mixing and exchange events.     

Community‐wide impacts of herbivore‐induced plant regrowth on arthropods in a multi‐willow species system

It has been widely accepted that herbivory induces morphological, phenological, and chemical changes in a wide variety of terrestrial plants. There is an increasing appreciation that herbivore‐induced plant responses affect the performance and abundance of other arthropods. However, we still have a poor understanding of the effects of induced plant responses on community structures of arthropods. We examined the community‐level effects of willow regrowth in response to damage by larvae of swift moth Endoclita excrescence (Lepidoptera: Hepialidae) on herbivorous and predaceous arthropods on three willow species, Salix gilgiana, S. eriocarpa and S. serissaefolia. The leaves of sprouting lateral shoots induced by moth‐boring had a low C:N ratio. The overall abundance and species richness of herbivorous insects on the lateral shoots were increased on all three willow species. Densities of specialist chewers and sap‐feeders, and leaf miners increased on the newly emerged lateral shoots. In contrast, the densities of generalist chewers and sap‐feeders, and gall makers did not increase. Furthermore, ant and spider densities, and the overall abundance and species richness of predaceous arthropods increased on the lateral shoots on S. gilgiana and S. eriocarpa, but not S. serissaefolia. In addition to finding that effects of moth‐boring on arthropod abundance and species richness varied among willow species, we also found that moth‐boring, willow species, and their interaction differentially affected community composition. Our findings suggest that moth‐boring has community‐wide impacts on arthropod assemblages across three trophic levels via induced shoot regrowth and increase arthropod species diversity in this three willow species system.     

Effects of Experience on Short‐ and Long‐term Foraging Performance in Bumblebees

Honeybees in natural settings show a gradual increase in foraging performance similar to the general pattern of lifetime performance seen in a wide variety of animals including humans. To quantify the factors contributing to such gradual increase in foraging success, we studied bumblebees foraging on pepper plants inside a greenhouse. This allowed us to combine the global measure of the net rate of food delivery to the hive with a detailed examination of bees’ performance at flowers over time. Although bees exhibited short‐term improvements in foraging ability during their first few foraging trips, we did not observe the predicted long‐term increase in performance over days. Our results suggest that a variety of flower‐handling tasks, flower choice and movements between plants can be learned quickly under the simple greenhouse settings. The long‐term increase in performance under natural settings may be caused by factors including spatial orientation and locating the best plant species, flower patches and individual plants over a large area.     

Long‐term effects of calorie restriction on serum sex‐hormone concentrations in men

Calorie restriction (CR) slows aging and consistently reduces circulating sex hormones in laboratory animals. However, nothing is known regarding the long‐term effects of CR with adequate nutrition on serum sex‐hormone concentration in lean healthy humans. In this study, we measured body composition, and serum total testosterone, total 17‐β‐estradiol, sex hormone–binding globulin (SHBG), and dehydroepiandrosterone sulfate (DHEA‐S) concentrations in 24 men (mean age 51.5 ± 13 years), who had been practicing CR with adequate nutrition for an average of 7.4 ± 4.5 years, in 24 age‐ and body fat–matched endurance runners (EX), and 24 age‐matched sedentary controls eating Western diets (WD). We found that both the CR and EX volunteers had significantly lower body fat than the WD volunteers (total body fat, 8.7 ± 4.2%; 10.5 ± 4.4%; 23.2 ± 6.1%, respectively; P = 0.0001). Serum total testosterone and the free androgen index were significantly lower, and SHBG was higher in the CR group than in the EX and WD groups (P ≤ 0.001). Serum 17β‐estradiol and the estradiol:SHBG ratio were both significantly lower in the CR and EX groups than in the WD group (P ≤ 0.005). Serum DHEA‐S concentrations were not different between the three groups. These findings demonstrate that, as in long‐lived CR rodents, long‐term severe CR reduces serum total and free testosterone and increases SHBG concentrations in humans, independently of adiposity. More studies are needed to understand the role of this CR‐mediated reduction in sex hormones in modulating the pathogenesis of age‐associated chronic diseases such as cancer and the aging process itself.     

Selective <Superscript>15</Superscript>N labeling of barstar in a T7 polymerase system

The T7 RNA polymerase system for selective protein labeling, previously optimized for the time of introducing the ¹⁵N amino acid relative to the inducer (IPTG) and host polymerase inhibitor (rifampicin), was further improved by the use of a special growth medium enriched in particular amino acids and by administration of an aminotransferase inhibitor (α-aminooxyacetic acid); the latter prevented isotope redistribution (as required by NMR studies) even with readily metabolized leucine. The approach is shown to be successful for selective labeling of barstar with [¹⁵N]Trp and [¹⁵N]Leu; it can be used with any proteins expressed in the T7 system.     

Long‐term moderate nutrient inputs enhance autotrophy in a forested Mediterranean stream

1. The effects of long‐term nutrient addition at moderate levels were examined in the food web of a forested Mediterranean stream. Basal concentrations of N and P were increased twofold (to c. 750 μg N) and threefold (to c. 30 μg P) from ambient concentrations in an experimental reach. Variations in the abundance of microbes (bacteria and algae), meiofauna and macrofauna, microbial processing of organic matter (extracellular enzyme activities) and stoichiometry of biofilms and invertebrates were compared to an upstream control reach during 4 years of artificial nutrient enhancement. 2. Effects were faster in the bacterial compartment but more substantial in the algal compartment. Epilithic algal biomass doubled in the enriched section jointly triggered by nutrients and increased light irradiance in winter and early spring. Only a few animal groups reacted to the enrichment, including the meiofaunal Copepoda, linked to their high use of enriched FPOM, and macrofaunal grazers (Ancylus), which followed the large algal biomass increase. 3. The enrichment caused biofilm phosphatase activity to decrease, while activities related to the use of algal‐related materials (peptidase, β‐glucosidase) increased. Enzymatic activities related to the use of allochthonous organic matter showed only minor and episodic increases. 4. Changes in stoichiometric ratios were apparent in the epilithic compartment, but not in the sand sediment or in the FPOM. Increases in P content were delayed for 9 months in epilithic biofilms and for nearly 2 years in the case of N. 5. After 2 years of enrichment, the flatworm Schmidtea polychroa (predator), oligochaetes (detritivore) and tadpoles of Bufo bufo (grazer) showed higher per cent N. 6. Enrichment effects were produced in spite of flow cessations that occurred commonly in summer. The results show that forested streams subjected to sustained (though minor) nutrient enrichment changed aspects of their biological structure and metabolism and that changes were especially favoured by periods when light was not limiting.     

Modelling the impacts of two exotic invasive species on a native butterfly: top-down vs. bottom-up effects

1. Exotic invasive species can influence population dynamics of native species through top-down or bottom-up forces. The present study examined separate and interactive effects of multiple exotic species invasions on the native mustard white butterfly, Pieris napi oleracea Harris (Lepidoptera: Pieridae), using a stochastic simulation model. 2. P. n. oleracea populations in North America have decreased regionally since the 1860s. Competition with an exotic congener (P. rapae L.), loss of native host plants and parasitism by the introduced broconid wasp (Cotesia glomerata L.), have been suggested to be independently responsible for its decline. The present study examined these hypotheses, as well as an alternative, invasion by an exotic crucifer, garlic mustard (Alliaria petiolata[Bieb.] Cavara & Grande). 3. A stochastic simulation model of P. n. oleracea population dynamics revealed that decreasing the number of host plants available for oviposition and larval development (i.e. habitat loss), sharply reduced the probability of populations persistence and decreased population size for those that persisted. 4. Simulated invasion by garlic mustard also substantially decreased both probability of persistence (= 0 at approximately 50% cover) and mean population size. Persistence probability never reached zero under any C. glomerata scenarios, even when larval mortality in the second generation due to parasitism was 100%. The impact of garlic mustard was intensified by the addition of C. glomerata parasitism. 5. Results suggest that bottom-up forces, loss of host plants through forest understorey loss and/or garlic mustard invasion are the most important forces driving P. n. oleracea population decline. Parasitism by C. glomerata may interact to reduce P. n. oleracea populations more rapidly, but appears insufficient alone to cause local extinction.     

Long‐term productivity of Mediterranean herbaceous vegetation after a single phosphorus application

Question: What is the mechanism that underlies long‐term maintenance of high herbaceous productivity after a single application of phosphorus (4.5 gP m^?2 and 9 gP m^?2) in a hilly Mediterranean environment in a phosphorus‐deficient ecosystem? Location: Inland, 15 km E of the Mediterranean coast, W Galilee, Israel (35°15′E, 33°01′N; 500 m asl). Methods: The experiment was established in 1988. Multi‐year data on above‐ground biomass, botanical composition, P content of vegetation and soil, and the grazing management context of the experiment were integrated to construct a feasible account of the P dynamics of the ecosystem. Results: The productivity of the herbaceous component already responded to P application in the first year. The effect on the shrubby component of the ecosystem was marginal. The available (bicarbonate extractable) P in the upper soil layer peaked in the year after application of P and then declined to the original level within 7 years. Despite the decline in available soil P, a high, fluctuating level of herbaceous biomass production was maintained for 20 years. Legume species (Fabaceae) became a prominent constituent of the herbaceous vegetation after the P pulse. Conclusions: The long‐term shift in productivity of the herbaceous component of the grazed ecosystem was triggered by a nutritional pulse that induced a feedback loop based on changes in botanical composition of the herbaceous vegetation, the animal–vegetation interaction, grazing and supplementary feeding regimen of the cattle.     

Back to the future: using palaeolimnology to infer long‐term changes in shallow lake food webs

1. Shallow lakes are often cited as classic examples of systems that exhibit trophic cascades but, whilst they provide good model systems with which to test general ecological theory and to assess long‐term community change, their food web linkages have rarely been resolved, so changes associated with the structure and dynamics of the ecological network as a whole are still poorly understood. 2. We sought to redress this, and to demonstrate the potential benefits of integrating palaeolimnological and contemporary data, by constructing highly resolved food webs and stable isotope derived measures of trophic interactions and niche space, for the extant communities of two shallow U.K. lakes from different positions along a gradient of eutrophication. The contemporary surface sediment cladoceran and submerged macrophyte assemblages in the less enriched site, Selbrigg Pond, matched the palaeolimnological assemblages of the more enriched site, Felbrigg Hall Lake, in its more pristine state during the 1920s. Thus, Selbrigg was a temporal analogue for Felbrigg, from which the consequences of long‐term eutrophication on food web structure could be inferred. These data represent the first steps towards reconstructing not only past assemblages (i.e. nodes within a food web), but also past interactions (i.e. links within a food web): a significant departure from much of the previous research in palaeolimnology. 3. The more eutrophic food web had far fewer nodes and links, and thus a less reticulate network, than was the case for the more pristine system. In isotopic terms, there was vertical compression in δ¹⁵N range (NR) and subsequent increased overlap in isotopic niche space, indicating increased trophic redundancy within Felbrigg. This structural change, which was associated with a greater channelling of energy through a smaller number of nodes as alternative feeding pathways disappear, could lead to reduced dynamic stability, pushing the network towards further simplification. These changes reflected a general shift from a benthic‐dominated towards a more pelagic system, as the plant‐associated subweb eroded. 4. Although these data are among the first of their kind, the palaeo‐analogue approach used here demonstrates the huge potential for applying food web theory to understand how and why these ecological networks change during eutrophication. Furthermore, because of the rich biological record preserved in their sediments, shallow lakes represent potentially important models for examining long‐term intergenerational dynamics, thereby providing a means by which models and data can be integrated on meaningful timescales – a goal that has long proved elusive in food web ecology.     

Long‐term warming and litter addition affects nitrogen fixation in a subarctic heath

Nitrogen (N) availability is the main constraint on primary production in most Arctic ecosystems, with microbial fixation of atmospheric N as the primary source of N input. However, there are only few reports on N fixation rates in relation to climate change in the Arctic. In order to investigate the effects of anticipated global climate change on N fixation rates in a subarctic moist heath, a field experiment was carried out in Northern Sweden. Warming was induced by plastic tents, and in order to simulate the effects of future increased tree cover, birch litter was added each fall for 9 years before the measurements. We analyzed N fixation rates on both whole‐ecosystem level and specifically on two moss species: Sphagnum warnstorfii and Hylocomium splendens. The whole‐ecosystem N fixation of the warmed plots almost tripled compared with the control plots. However, in the Sphagnum and Hylocomium mosses we observed either no change or occasionally even a decrease in N fixation after warming. Both measured on whole‐ecosystem level and on the two moss species separately, litter addition increased N fixation rates. The results suggest that warming will lead to a general increased ecosystem N input, but also that the N fixation associated to some moss species is likely to decrease. Hence, this study shows that the scale of measurements is crucial when investigating on ecosystem responses to manipulations.     

Singlet oxygen,a neglected but important environmental factor: short‐term and long‐term effects on bacterioplankton composition in a humic lake

Photolysis of dissolved organic matter (DOM) leads to contrasting effects on bacterioplankton dynamics, i.e. stimulation and inhibition of bacterial activity. In particular, the role of short‐lived reactive oxygen species (ROS), e.g. singlet oxygen (¹O₂), in altering microbial activity and species composition has scarcely been investigated. Therefore, we have artificially increased the natural rate of ¹O₂ formation in short‐term (～4 h) in situ and long‐term (72 h) laboratory incubations of surface water samples from a humic acid‐rich lake. Denaturing gradient gel electrophoresis (DGGE) patterns revealed significant changes in occurrence of abundant bacterioplankton phylotypes upon ¹O₂ exposure. Cluster analysis of DGGE patterns showed that a moderate increase in ¹O₂ exposure leads to similar changes in different years indicating the establishment of bacterial communities adapted to ¹O₂ exposure. Bacterioplankton phylotypes favoured under these conditions belonged to Betaproteobacteria of the beta II cluster (e.g. Polynucleobacter necessarius) and the beta I cluster related to Limnohabitans (R‐BT subcluster) as well as Alphaproteobacteria affiliated to Novosphingobium acidiphilum. In contrast, Actinobacteria of the freshwater acI‐B cluster were sensitive even against moderate ¹O₂ exposure. We conclude that ¹O₂ exposure due to DOM photolysis represents an important natural selective factor affecting bacterial species dynamics in aquatic ecosystems in many ways.     

Trophic positioning and microphytobenthic carbon uptake of biofilm‐dwelling meiofauna in a temperate river

1. δ¹³C and δ¹⁵N stable isotope signatures combined with an in situ microphytobenthic ¹³C labelling experiment were performed on epilithic biofilms of a large temperate river (the Garonne, France) to infer the trophic positioning of biofilm‐dwelling meiofauna and their uptake of microphytobenthic carbon. 2. Chironomidae larvae and Chromadorina spp. nematodes rapidly incorporated freshly produced microphytobenthic carbon in contrast to Rhyacophilidae larvae and Naididae oligochaetes. Quantitatively, macrofaunal Chironomidae incorporated more microphytobenthic carbon per day than did meiofauna. Moreover, Chironomidae seemed more involved in the spatial export of microphytobenthic carbon than nematodes. 3. Rhyacophilidae larvae were predators feeding on large meiofauna (Naididae and Chironomidae) but not on nematodes. Naididae oligochaetes primarily gained their carbon from allochthonous and/or microbial‐loop recycled sources. 4. A rapid and significant loss of labelled microphytobenthic carbon was observed. Feeding activity of biofilm‐dwelling invertebrates seemed not to be primarily involved in this loss.     

Long‐term stock grazing management in Travelling Stock Reserves and influence on conservation values

We examined the nature of long‐term grazing management implemented in 51 Travelling Stock Reserves (TSRs) in the Albury region, and investigated potential relationships between grazing intensity and conservation values. In general, grazing intensities in most TSRs decreased over the 22 year study period. Most TSRs were lightly grazed (density = 1.1 DSE/ha/year), and stocked for <2 months per year, but some were much more heavily grazed. Spring grazing intensity was found to be negatively associated with TSR conservation values. Our results suggest that grazing management aims to achieve both production and conservation outcomes are not necessarily exclusive to each other.