Set Of Mesocosms Research Articles

Food Preferences in Two Detritivore Species: Laboratory Choice Tests Using Leaf Litters of Different Tree Species

Soil fauna, including terrestrial isopods, millipedes and earthworms, play an important role in the decomposition of litter through the process of shredding it during consumption. In the present study, the food preferences in two detritivores, the common woodlouse (Oniscus asellus) and the earthworm (Lumbricus rubellus) over the leaf litter of four common tree species: common black alder (Alnus glutinosa), silver birch (Betula pendula), small-leaved linden (Tilia cordata) and pedunculate oak (Quercus robur) were quantified in the laboratory. For each animal species, two sets of feeding mesocosms were prepared: one set with single litter species and another with mixed litter material (cafeteria-type test), where the animals were allowed to choose among the four litter species at once. The food preferences of the studied animals were determined on the basis of the consumption (mass loss) of litter for each litter species at the end of two-weeks lasting experiments. The results showed that the litter mass losses in both detritivores were significantly influenced by the tree species. The litter mass losses can be ranked in descending order as follows: alder, birch, linden, oak. In the case of O. asellus, litter mixing had no effect on litter mass loss when compared to single alder and birch litter, however mixing clearly accelerated litter mass loss compared to single lime or oak litter. For L. rubellus, litter mixing was found to slow litter mass loss compared to each single alder, birch and lime litter, while accelerating litter mass loss compared to single oak litter. For the interpretation of the results, the literature data on carbon to nitrogen ratio, as well as the proportion of difficult-to-degrade polyphenols and lignins in leaves of the studied tree species were used.

Influence of slurry acidification with H2SO4 on soil pH, N, P, S, and C dynamics: Incubation experiment

Acidifying slurry with sulfuric acid (H2SO4) is practiced in some countries for reducing ammonia (NH3) emissions during slurry storage and spreading to land. However, knowledge on how the application of acidified slurry affects soil health and nutrient cycling is lacking. This is particularly important since acidification with H2SO4 can substitute a sulfur (S) mineral fertilizer to increasingly S-deficient agricultural soils. We hypothesized that (ⅰ) slurry acidification would decrease the soil pH over a prolonged period, and as a result (ⅱ) would increase the extractable N, P, C and S concentrations, (ⅲ) and decrease greenhouse gas emissions. By using laboratory mesocosms, the nutrient (C, N, P and S) dynamics were monitored in an arable sandy clay loam soil receiving acidified and non-acidified cattle slurry in a 2-month incubation. Estimations of greenhouse gas emissions (CO2, CH4, N2O), soil-pore- water components (NO3−, NH4+, PO43−, SO42−, DOC, DON, pH) were performed on static mesocosms. In addition, a parallel set of mesocosms were used for soil extractions using distilled water and 0.5 M K2SO4. There were six treatments: (1) soil (control), (2) soil + slurry, (3) soil + acidified slurry (with H2SO4, pH =5.5), (4) soil + HCl, (5) soil + K2SO4, and (6) soil + K2SO4 + H2SO4. Our results showed that over the incubation, slurry acidification reduced soil pH by at least 0.4 units. Water soluble PO43−-P concentration was also reduced, whilst extractable DOC and NO3—N concentrations were increased; the latter as a result of stimulated N mineralization in the acidification treatments (3, 4 and 6). Differences in water soluble SO42- -S concentrations per treatment were not significant over time.Slurry acidification did not significantly affect N2O emissions but decreased net CO2 and CH4 emissions leading to an overall reduction in the soil's total greenhouse gas footprint (expressed as CO2e). We conclude that application of acidified slurry to soil can reduce soil pH by at least 0.4 pH units for up to 2-months before it is buffered back to the pH level of the soil that received the non-acidified slurry. In addition to increasing organic N mineralization with limited impacts on P and S dynamics of the soil and the slurry.

Warming and parasitism impair the performance of Baltic native and invasive macroalgae and their associated fauna

AbstractGlobal warming, bioinvasions, and parasitism affect single‐species performances and species interactions, substantially impacting the structure and stability of marine ecosystems. In light of accelerated global change, the information derived from studies focusing on single species and single drivers is insufficient, calling for a multi‐stressor approach under near‐natural conditions. We investigated the effects of warming (+3°C) on the performance of a benthic community composed of native and invasive macroalgae, consumers and a trematode parasite in a mesocosm setting. We also assessed the effects of warming and parasitism on the survival and growth of gastropods and mussels and the thermal dependency of trematode performance. Our findings show that warming and grazing by infected gastropods had a large detrimental effect on the invasive macroalga growth. Furthermore, the single and interactive effects of parasitism and warming were detrimental to intermediate host survival and growth, especially to large mussels. Finally, cercarial emergence positively correlated to the natural peaks of summer temperatures, while infection intensity in mussels was higher in larger individuals. Our findings suggest that grazing and warming will be detrimental to the invasive macroalga, favoring the native alga. Moreover, parasitism will enhance grazing, especially in summer, when higher temperatures trigger parasite development. However, parasite‐enhanced grazing may be buffered by higher mortality or a shift in the size of infected intermediate hosts under warming. Our findings demonstrate how complex effects of ocean warming can be on food webs and how they can be mediated by parasitism and, as a result, influence native and invasive macroalgae differently.

Aboveground wetland vegetation growth responses to simulated sediment diversion inundation scenarios

Coastal Louisiana is experiencing extremely high rates of wetland loss, particularly within the Mississippi River Deltaic Plain. Although multiple stressors contribute to this loss, one major driver is decreased wetland elevation stemming from disconnection of recurrent sediment rich influxes of Mississippi River floodwater. The decrease in sediment delivery, in conjunction with natural subsidence processes, reduce marsh elevations and increase flooding stress on vegetation, leading to marsh collapse. River sediment diversions are large-scale restoration techniques intended to rehabilitate Louisiana's degraded coastal wetlands by mimicking historic crevasse splays, thereby stimulating land building and vegetation growth. However, such large-scale restoration techniques require an appropriate knowledge base of vegetation and soil biogeochemical responses to altered environmental conditions. In this research, monospecific sods of three foundational marsh species (Spartina patens, Spartina alterniflora, Typha latifolia) were exposed to inundation depth (20 and 40 cm), duration (8 and 16 weeks), and salinity (0 and 5 psu) treatments consistent with a range of anticipated sediment diversion scenarios in a mesocosm setting. Additionally, sods were monitored through week 20 after being removed from their experimental conditions. Both Spartina alterniflora and Typha latifolia displayed relatively consistent increases in stem densities over time across inundation depth-duration treatments, whereas Spartina patens displayed a sharp decline in stem densities at 40 cm flooding depths. Additionally, both Spartina alterniflora and Spartina patens had the least observed amount of total aboveground biomass at 40 cm flooding depths. Spartina patens sods displayed a significant loss in surface elevation with increased flooding stress through study week 20, whereas Typha latifolia demonstrated a significant gain in surface elevation. These results suggest that restoration projects increasing inundation within the limits of the depths employed herein and the anticipated duration of river diversion induced inundation are unlikely to negatively impact the aboveground growth responses of Spartina alterniflora and Typha latifolia, but could reduce stem densities and aboveground biomass of Spartina patens.

Hyperspectral reflectance dataset of pristine, weathered, and biofouled plastics

Abstract. This work presents a hyperspectral reflectance dataset of macroplastic samples acquired using Analytical Spectral Devices (ASD) FieldSpec 4. Samples analyzed consisted of pristine, artificially weathered, and biofouled plastic items and plastic debris samples collected in the docks of the Port of Antwerp and in the river Scheldt near Temse Bridge (Belgium). The hyperspectral signal of each sample was measured in controlled dry conditions in an optical calibration facility at the Vlaamse Instelling voor Technologisch Onderzoek (VITO; Flemish Institute for Technological Research) and, for a subset of plastics, under wet and submerged conditions in a silo tank at Flanders Hydraulics. The wet and submerged hyperspectral signals were measured in a mesocosm setting that mimicked environmentally relevant concentrations of freshwater microalgae and suspended sediment. The ASD was equipped with an 8∘ field of view at the calibration facility, and a 1∘ field of view was used in the mesocosm setting. The dataset obtained complies with the FAIR (Findable, Accessible, Interoperable, Reusable) principles and is available in the open-access repository Marine Data Archive (https://doi.org/10.14284/530, Leone et al., 2021).

Mesopredator‐mediated trophic cascade can break persistent phytoplankton blooms in coastal waters

Managing eutrophied systems using only nutrient decreases to impose bottom–up control can be economically and ecologically challenging. Top–down controls through increased consumption have sometimes effectively controlled phytoplankton blooms. However, mechanistic insights, especially on possible trophic cascades, are less understood in brackish, species‐poor coastal waters, where large cladocera are absent. In this study, we set‐up large mesocosms for three consecutive years during the growing season. One set of mesocosms contained mesopredators (gobies and shrimps), whereas the other mesocosms had no such mesopredator present. The results were standardized to monitoring data from the ecosystem to track possible differences between treatments and the system. We found that mesopredator mesocosms showed lower turbidity, phytoplankton biomass and nutrients compared to no‐mesopredator mesocosms, and compared to the ecosystem. This decrease allowed macrophytes to colonize water depths only sparsely colonized in the ecosystem. Rotifer biomass increased in mesopredator mesocosms compared to the ecosystem and to the no‐mesopredator mesocosms. Likewise, copepod biomass that potentially grazes upon rotifers and other microzooplankton decreased in mesopredator mesocosms. No‐mesopredator mesocosms were colonized by an omnivorous mesograzer Gammarus tigrinus, potentially creating additional pressure on macrophytes and increasing grazing‐mediated nutrient release. Zooplankton was not able to control the non‐nutrient limited phytoplankton. We propose a new mechanism, where a higher mesopredator density will increase grazing on phytoplankton by promoting microzooplankton capable of grazing on picophytoplankton. This proposed mechanism would contrast with freshwater systems, where a decrease of zooplanktivorous fish would promote larger phytoplankton grazer like cladocera. Biomanipulation in such species‐poor eutrophic coastal waters may be more successful, due to less trophic pathways, that can cause complex top–down controls like in other systems. Stocking eutrophic coastal waters with gobies and shrimps may be an alternative biomanipulative approach rather than selectively removing large piscivorous or omnivorous fish from eutrophic coastal waters.

American frogbit response to herbicides

Limnobium spongia (frogbit) is a free-floating aquatic plant that can produce extensive floating mats causing negative ecological, social, and economic impacts that can harm aquatic fauna (i.e., dissolved oxygen depletion) and restrict human uses of water. Literature describing effective control measures for frogbit is minimal. Efficacy of high and low doses of seven foliar-applied herbicides (2,4-D, florpyraux-ifen-benzyl, flumioxazin, glyphosate, imazamox, imazapyr, and triclopyr) were evaluated in a mesocosm setting in the summers of 2018, 2020, and 2021. Both emergent and submersed frogbit biomass were reduced at least 99% by imazamox (0.56 and 1.11 kg ai ha􀀁1) and imazapyr (0.42 and 0.84 kg ae ha􀀁1) 8 wk after treatment (WAT) compared with nontreated reference plants. Triclopyr (6.71 kg ae ha􀀁1) reduced frogbit biomass 92% and flumioxazin (0.42 kg ai ha􀀁1) reduced biomass 87 to 93% compared with reference plants. 2,4-D (2.12 and 4.24 kg ae ha􀀁1), glyphosate (2.83 and 5.67 kg ai ha􀀁1), triclopyr (3.36 kg ae ha􀀁1), florpyrauxifen-benzyl (0.02 and 0.05 kg ai ha􀀁1), and flumioxazin (0.21 kg ai ha􀀁1) did not reduce frogbit biomass 8 WAT compared with reference plants. Future research should consider the efficacy of different herbicide combinations to control frogbit, as well as the role of diluent volume per unit area, especially with imazamox and imazapyr. Field studies also will be useful in determining whether the results observed in this study will translate to management of frogbit in natural settings.

Un-biodegradable and biodegradable plastic sheets modify the soil properties after six months since their applications

Nowadays, microplastics represent emergent pollutants in terrestrial ecosystems that exert impacts on soil properties, affecting key soil ecological functions. In agroecosystems, plastic mulching is one of the main sources of plastic residues in soils. The present research aimed to evaluate the effects of two types of plastic sheets (un-biodegradable and biodegradable) on soil abiotic (pH, water content, concentrations of organic and total carbon, and total nitrogen) and biotic (respiration, and activities of hydrolase, dehydrogenase, β-glucosidase and urease) properties, and on phytotoxicity (germination index of Sorghum saccharatum L. and Lepidium sativum L.). Results revealed that soil properties were mostly affected by exposure time to plastics rather than the kind (un-biodegradable and biodegradable) of plastics. After six months since mesocosm setting up, the presence of un-biodegradable plastic sheets significantly decreased soil pH, respiration and dehydrogenase activity and increased total and organic carbon concentrations, and toxicity highlighted by S. saccharatum L. Instead, the presence of biodegradable plastic sheets significantly decreased dehydrogenase activity and increased organic carbon concentrations. An overall temporal improvement of the investigated properties in soils covered by biodegradable plastic sheets occurred.

Measuring Daphnia life history in the wild: The efficacy of individual field cages.

Life‐history studies are often conducted in a laboratory environment where it is easy to assay individual animals. However, factors such as temperature, photoperiod, and nutrition vary greatly between laboratory and field environments, making it difficult to compare results. Consequently, there is a need to study individual life histories in the field, but this is currently difficult in systems such as Daphnia where it is not possible to mark and track individual animals. Here, we present a proof of principle study showing that field cages are a reliable method for collecting individual‐level life‐history data in Daphnia magna. As a first step, we compared the life history of paired animals reared outside and inside cages to test the hypothesis that cages allow free flow of algal food resources. We then used a seminatural mesocosm setting to compare the performance of individual field cages versus glass jars refilled with mesocosm water each day. We found that cages did not inhibit food flow and that differences in life histories between three clones detected in the jar assays were also detectable using the much less labor‐intensive field cages. We conclude that field cages are a feasible approach for collecting individual‐level life‐history data in systems such as Daphnia where individual animals cannot be marked and tracked.

Ecological significance of extracellular vesicles in modulating host-virus interactions during algal blooms

Extracellular vesicles are produced by organisms from all kingdoms and serve a myriad of functions, many of which involve cell-cell signaling, especially during stress conditions and host-pathogen interactions. In the marine environment, communication between microorganisms can shape trophic level interactions and population succession, yet we know very little about the involvement of vesicles in these processes. In a previous study, we showed that vesicles produced during viral infection by the ecologically important model alga Emiliania huxleyi, could act as a pro-viral signal, by expediting infection and enhancing the half-life of the virus in the extracellular milieu. Here, we expand our laboratory findings and show the effect of vesicles on natural populations of E. huxleyi in a mesocosm setting. We profile the small-RNA (sRNA) cargo of vesicles that were produced by E. huxleyi during bloom succession, and show that vesicles applied to natural assemblages expedite viral infection and prolong the half-life of this major mortality agent of E. huxleyi. We subsequently reveal that exposure of the natural assemblage to E. huxleyi-derived vesicles modulates not only host-virus dynamics, but also other components of the microbial food webs, thus emphasizing the importance of extracellular vesicles to microbial interactions in the marine environment.

Impacts of Petroleum, Petroleum Components, and Dispersants on Organisms and Populations

Following the Deepwater Horizon blowout, oil, degraded oil, oil mixed with dispersants, and management responses to the spill affected a variety of Gulf of Mexico organisms. This review provides examples of various documented impacts, common patterns, and trends across organisms and/or their environments, and discusses future implications as well as directions for future research. Organism effects are generally characterized as lethal and sublethal. Sublethal can be short term, long term, or permanent and multigenerational. We present individual examples of effects on behavioral response, olfaction, vision, cardiac function, and gene shift, based on research done in laboratories, mesocosm settings, and the field. Future research should emphasize collection and analysis of routine toxicological baselines and examine how and if molecular impacts cascade up to populations. This research will require development of rapid molecular tools and testing procedures to determine exposure compared to field-relevant exposure levels and to be able to extrapolate laboratory results to the field, especially given the mosaic of differing contaminant concentrations (below, at, or exceeding critical concentrations that result in lethal or sublethal effects) occurring in the environment. Recent chemical studies have identified a detectable suite of polycyclic aromatic hydrocarbon metabolites for which there are no toxicity data; further research is needed to determine their impacts on food webs.

A comparison of the Trojan Y Chromosome strategy to harvesting models for eradication of nonnative species

AbstractThe Trojan Y Chromosome strategy (TYC) is a promising eradication method for biological control of nonnative species. The strategy works by manipulating the sex ratio of a population through the introduction ofsupermalesthat guarantee male offspring. In the current study, we compare the TYC method with a pure harvesting strategy. We also analyze a hybrid harvesting model that mirrors the TYC strategy. The dynamic analysis leads to results on stability of solutions and bifurcations of the model. Several conclusions about the different strategies are established via optimal control methods. In particular, the results affirm that either a pure harvesting or hybrid strategy may work better than the TYC method at controlling a nonnative species population.Recommendations for resource managersWhere harvesting is feasible, it is as effective if not more effective than the classical TYC method. Therein managers may attempt harvesting female fish while stocking males or harvesting both male and female fishes.Managers may attempt linear harvesting, saturating density‐dependent harvesting, and unbounded density‐dependent harvesting. Linear harvesting is seen to be the most effective.We caution against the outright use of harvesting due to various density‐dependent effects that may arise. To this end hybrid models that involve a combination of harvesting and TYC‐type methods might be a better strategy.One may also use harvesting as a tool in mesocosm settings to predict the efficacy of the TYC strategy in the wild.

Effects of the Bioturbating Marine Yabby Trypaea australiensis on Sediment Properties in Sandy Sediments Receiving Mangrove Leaf Litter

Laboratory mesocosm incubations were undertaken to investigate the influence of burrowing shrimp Trypaea australiensis (marine yabby) on sediment reworking, physical and chemical sediment characteristics and nutrients in sandy sediments receiving mangrove (Avicennia marina) leaf litter. Mesocosms of sieved, natural T. australiensis inhabited sands, were continually flushed with fresh seawater and pre-incubated for 17 days prior to triplicates being assigned to one of four treatments; sandy sediment (S), sediment + yabbies (S+Y), sediment + leaf litter (organic matter; S+OM) and sediment + yabbies + leaf litter (S+Y+OM) and maintained for 55 days. Mangrove leaf litter was added daily to treatments S+OM and S+Y+OM. Luminophores were added to mesocosms to quantify sediment reworking. Sediment samples were collected after the pre-incubation period from a set of triplicate mesocosms to establish initial conditions prior to the imposition of the treatments and from the treatment mesocosms at the conclusion of the 55-day incubation period. Yabbies demonstrated a clear effect on sediment topography and leaf litter burial through burrow creation and maintenance, creating mounds on the sediment surface ranging in diameter from 3.4 to 12 cm. Within S+Y+OM sediments leaf litter was consistently removed from the surface to sub-surface layers with only 7.5% ± 3.6% of the total mass of leaf detritus added to the mesocosms remaining at the surface at the end of the 55-day incubation period. Yabbies significantly decreased sediment wet-bulk density and increased porosity. Additionally, T. australiensis significantly reduced sediment bio-available ammonium (NH4+bio) concentrations and altered the shape of the concentration depth profile in comparison to the non-bioturbated mesocosms, indicating influences on nutrient cycling and sediment-water fluxes. No significant changes for mean apparent biodiffusion coefficients (Db) and mean biotransport coefficients (r), were found between the bioturbated S+Y and S+Y+OM mesocosms. The findings of this study provide further evidence that T. australiensis is a key-species in shallow intertidal systems playing an important role as an ‘ecosystem engineer’ in soft-bottom habitats by significantly altering physical and chemical structures and biogeochemical function.

The impact of dispersal, plant genotype and nematodes on arbuscular mycorrhizal fungal colonization

While the majority of parasitic and mutualistic microbes have the potential for long-range dispersal, the high turnover in community composition among nearby hosts has often been interpreted to reflect dispersal constraints. To resolve this apparent contradiction, we need further insights into the relative importance of dispersal limitation, host genotype and the biotic environment on the colonization process. We focused on the important root symbionts, the arbuscular mycorrhizal (AM) fungi. We studied AM fungal colonization ability in a controlled mesocosm setting, where we placed Plantago lanceolata plants belonging to four different genotypes in sterile soil at 10, 30 and 70 cm from a central AM fungal inoculated P. lanceolata plant. In part of the mesocosms, we also inoculated the source plants with nematodes. AM fungi colonized receiver plants <1 m away over the course of ten weeks, with a strong effect of distance from source plant on AM fungal colonization. Plant genotype influenced AM fungal colonization during the early stages of colonization, while nematode inoculation had no effect on AM fungal colonization. Overall, the effect of both dispersal limitation and plant genetic variation may underlie the small-scale heterogeneity found in natural AM fungal communities.

Exposure to microplastics reduces attachment strength and alters the haemolymph proteome of blue mussels (Mytilus edulis)

The contamination of marine ecosystems with microplastics, such as the polymer polyethylene, a commonly used component of single-use packaging, is of global concern. Although it has been suggested that biodegradable polymers, such as polylactic acid, may be used to replace some polyethylene packaging, little is known about their effects on marine organisms. Blue mussels, Mytilus edulis, have become a “model organism” for investigating the effects of microplastics in marine ecosystems. We show here that repeated exposure, over a period of 52 days in an outdoor mesocosm setting, of M. edulis to polyethylene microplastics reduced the number of byssal threads produced and the attachment strength (tenacity) by ∼50%. Exposure to either type of microplastic altered the haemolymph proteome and, although a conserved response to microplastic exposure was observed, overall polyethylene resulted in more changes to protein abundances than polylactic acid. Many of the proteins affected are involved in vital biological processes, such as immune regulation, detoxification, metabolism and structural development. Our study highlights the utility of mass spectrometry-based proteomics to assess the health of key marine organisms and identifies the potential mechanisms by which microplastics, both conventional and biodegradable, could affect their ability to form and maintain reefs.

Tolerance of tropical seagrasses Zostera muelleri and Halophila ovalis to burial: Toward an understanding of threshold effects

Seagrass meadows are critically important coastal habitats, but they are undergoing rapid global declines linked to degradation of coastal catchments and the expansion of development in coastal zones, which can lead to increased deposition of terrigenous sediments onto seagrass meadows. In the Asia-Pacific region, which includes the Great Barrier Reef, direct sedimentation effects are recognised as the major threat to seagrass growth and survival. However, tolerance to burial varies among species. Understanding thresholds for burial tolerance at the species-level is therefore critical to effective management of human impacts on seagrass meadows. This research examined the effects of sedimentation on two tropical seagrass species, Zostera muelleri and Halophila ovalis in an experimental mesocosm and field setting. The research suggests that shoot density in these species declines significantly at burial depths of 5–7.5 mm in a mesocosm setting, with very low levels of growth observed above 10 mm burial depth. Fine sediments (including fine sands, silts and clays) appear to have a greater negative effect on shoot density in both species, compared to coarser sandy sediments. In situ, the effect of burial is less pronounced and is likely to be mitigated by a range of factors, including clonal integration. These species also demonstrate different adaptations to burial disturbance, including by resisting burial effects (Z. muelleri) or by regenerating from the buried rhizome after disturbance (H. ovalis).

Combined effects of local habitat, anthropogenic stress, and dispersal on stream ecosystems: a mesocosm experiment.

The effects of anthropogenic stressors on community structure and ecosystem functioning can be strongly influenced by local habitat structure and dispersal from source communities. Catchment land uses increase the input of fine sediments into stream channels, clogging the interstitial spaces of benthic habitats. Aquatic macrophytes enhance habitat heterogeneity and mediate important ecosystem functions, being thus a key component of habitat structure in many streams. Therefore, the recovery of macrophytes following in-stream habitat modification may be prerequisite for successful stream restoration. Restoration success is also affected by dispersal of organisms from the source community, with potentially the strongest responses in relatively isolated headwater sites that receive a limited amount of dispersing individuals. We used a factorial design in a set of stream mesocosms to study the independent and combined effects of an anthropogenic stressor (sand sedimentation), local habitat (macrophytes, i.e., moss transplants), and enhanced dispersal (two levels: high vs. low) on organic matter retention, algal accrual rate, leaf decomposition, and macroinvertebrate community structure. Overall, all responses were simple additive effects with no interactions between treatments. Sand reduced algal accumulation, total invertebrate density, and density of a few individual taxa. Mosses reduced algal accrual rate and algae-grazing invertebrates, but enhanced organic matter retention and the number of detritus and filter feeders. Mosses also reduced macroinvertebrate diversity by increasing the dominance by a few taxa. Mosses reduced leaf mass loss, possibly because the organic matter retained by mosses provided an additional food source for leaf-shredding invertebrates and thus reduced shredder aggregation into leaf packs. The effect of mosses on macroinvertebrate communities and ecosystem functioning was distinct irrespective of the level of dispersal, suggesting strong environmental control of community structure. The strong environmental control of macroinvertebrate community composition even under enhanced dispersal suggests that re-establishing key habitat features, such as natural stream vegetation, could aid ecosystem recovery in boreal streams.

Influence of flow on locomotion, feeding behaviour and spatial distribution of a suspension-feeding sea cucumber

Although movement in response to environmental conditions represents a fundamental link between animal behaviour and population ecology, it is rarely investigated in suspension feeders because they are generally perceived as sessile. Here, the interplay between water flow and fine locomotor and feeding behaviours was experimentally investigated for the first time in a free-moving suspension-feeding sea cucumber (Cucumaria frondosa; Echinodermata, Holothuroidea) using time-lapse videography in a mesocosm setting. Individuals moved away from static conditions in the weakest flow treatment and fled the strongest flows (>40 cm s-1) in the more dynamic treatments. The tentacles of individuals located in areas with flows of ≥40 cm s-1 was aligned with the direction of the current, whereas in flows <40 cm s-1, they were typically perpendicular to the direction of flow. Tentacle deployment and insertion rates (i.e. feeding rate) increased with flow, from 0.95 min-1 at 10 cm s-1 to 1.13 min-1 at 40 cm s-1 Three modes of locomotion were detected. Forward crawling was most frequent at flows ≤40 cm s-1, passive rolling dominated at flows >40 cm s-1 and active rolling occurred randomly at flows between 0 and 120 cm s-1 Overall, the flow regime favoured by C . frondosa was determined to be between 21 and 40 cm s-1, under which an optimal balance between efficient food capture and energy expenditure for attachment to the bottom was presumably found. These findings provide insight into the distribution and population dynamics of suspension-feeding holothuroids, and may also assist the fisheries management and aquaculture development of commercial species.

Bacterial communities in soil become sensitive to drought under intensive grazing

Increasing climatic and anthropogenic pressures on soil ecosystems are expected to create a global patchwork of disturbance scenarios. Some regions will be strongly impacted by climate change, others by agricultural intensification, and others by both. Soil microbial communities are integral components of terrestrial ecosystems, but their responses to multiple perturbations are poorly understood. Here, we exposed soils from sustainably- or intensively-managed grasslands in an agro-silvo-pastoral oak woodland to month-long intensified drought and flood simulation treatments in a controlled mesocosm setting. We monitored the response of the bacterial communities at the end of one month as well as during the following month of recovery. The communities in sustainably-managed plots under all precipitation regimes were richer and more diverse than those in intensively-managed plots, and contained a lower proportion of rapidly-growing taxa. Soils from both land managements exhibited changes in bacterial community composition in response to flooding, but only intensively-managed soils were affected by drought. The ecologies of bacteria favored by both drought and flood point to both opportunism and stress tolerance as key traits shaping the community following disturbance. Finally, the response of several taxa (i.e. Chloracidobacteria RB41, Janthinobacterium sp.) to precipitation depended on land management, suggesting that the community itself affected individual disturbance responses. Our findings provide an in-depth view of the complexity of soil bacterial community responses to climatic and anthropogenic pressures in time, and highlight the potential of these stressors to have multiplicative effects on the soil biota.

Experimental Assessment in Nature of the Ecological Effects of a Specialist Parasite

Parasites can have important effects on the structure and composition of natural biological communities, either directly by influencing host fecundity and survival (i.e., density-mediated effects) or indirectly by influencing host traits such as behavior, life-history, morphology, and physiology (i.e., trait-mediated effects). Yet few studies have explored how these effects play out in the wild, as opposed to simplified and controlled laboratory or mesocosm settings. We addressed this information gap by translocating Gyrodactylus ectoparasites of the Trinidadian guppy into previously Gyrodactylus-free guppy populations in two rivers (Marianne and Paria) in the Northern Mountain Range in Trinidad. We then measured phenotypic and demographic changes in the guppy host and its competitor, Rivulus hartii, and compared these changes to guppies and Rivulus in control reaches just upstream. In the Marianne, where guppies invest more in reproduction (i.e., greater size and number of embryos), the introduction of G...