Catchment geology preconditions spatio-temporal heterogeneity of ecosystem functioning in forested headwater streams

Catchment geology can affect water chemistry and groundwater influence, eventually affecting macroinvertebrate communities, but its effects on stream functions such as leaf decomposition have been scarcely investigated. To understand the effects of geology on leaf decomposition, we conducted leaf litter experiments in streams with volcanic and non-volcanic substrata using fine and coarse mesh bags. Volcanic spring-fed streams showed lower temperature in summer and higher temperature in winter (with temperature difference being more pronounced later in incubation) than non-volcanic streams. Macroinvertebrate communities captured inside coarse litter bags differed in the two stream types in both seasons, mainly because of shredder communities. Shredder abundance and biomass were higher in volcanic streams in both seasons. Geology-dependent temperature influenced microbe-mediated decomposition in both seasons, with total phosphorus as an additional driver in winter. Summer temperature was associated with an overall positive effect on the abundance of shredders, which affected invertebrate-mediated decomposition, but this was not evident in winter. Shredder activity in volcanic streams compensated for temperature-dependent microbial activity resulting in an overall balance in leaf decomposition. Spring-fed systems are valuable ecosystems, particularly for cold-adapted species. Thus, understanding these understudied ecosystems will significantly aid in their appropriate conservation

Research priorities for freshwater mussel conservation assessment

Freshwater mussels are declining globally, and effective conservation requires prioritizing research and actions to identify and mitigate threats impacting mussel species. Conservation priorities vary widely, ranging from preventing imminent extinction to maintaining abundant populations. Here, we develop a portfolio of priority research topics for freshwater mussel conservation assessment. To address these topics, we group research priorities into two categories: intrinsic or extrinsic factors. Intrinsic factors are indicators of organismal or population status, while extrinsic factors encompass environmental variables and threats. An understanding of intrinsic factors is useful in monitoring, and of extrinsic factors are important to understand ongoing and potential impacts on conservation status. This dual approach can guide conservation status assessments prior to the establishment of priority species and implementation of conservation management actions.NF-R was supported by a post-doctoral fellowship (Xunta de Galicia Plan I2C 2017-2020, 09.40.561B.444.0) from the government of the autonomous community of Galicia. BY was supported by the Ministry of Science and Higher Education (no. 0409-2016-0022). DLS was supported by the G. E. Hutchinson Chair at the Cary Institute of Ecosystem Studies. AO was supported by the Russian Foundation for Basic Research (no. 17-44-290016). SV was funded by European Investment Funds by FEDER/COMPETE/POCI- Operacional Competitiveness and Internacionalization Programme, under Project POCI-01-0145-FEDER-006958 and National Funds by FCT-Portuguese Foundation for Science and Technology, under the project UID/AGR/04033/2013. NF-R is very grateful to the University of Oklahoma Biological Survey for providing space to work in the U.S. and especially to Vaughn Lab members. Authors are very grateful to Akimasa Hattori, Allan K. Smith, Andrew Roberts, Daniel Graf, David Stagliano, David T. Zanatta, Dirk Van Damme, Ekaterina Konopleva, Emilie Blevins, Ethan Nedeau, Frankie Thielen, Gregory Cope, Heinrich Vicentini, Hugh Jones, Htilya Sereflisan, Ilya Vikhrev, John Pfeiffer, Karen Mock, Mary Seddon, Katharina Stockl, Katarzyna Zajac, Kengo Ito, Marie Capoulade, Marko Kangas, Michael Lange, Mike Davis, Pirkko-Liisa Luhta, Sarina Jepsen, Somsak Panha, Stephen McMurray, G. Thomas Watters, Wendell R. Haag, and Yoko Inui for their valuable contribution in the initial selection and description of extrinsic and intrinsic factors. We also wish to thank Dr. Amanda Bates, Chase Smith, and two anonymous reviewers for comments on earlier drafts of this manuscript. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government

Latitude dictates plant diversity effects on instream decomposition

Running waters contribute substantially to global carbon fluxes through decomposition of terrestrial plant litter by aquatic microorganisms and detritivores. Diversity of this litter may influence instream decomposition globally in ways that are not yet understood. We investigated latitudinal differences in decomposition of litter mixtures of low and high functional diversity in 40 streams on 6 continents and spanning 113 degrees of latitude. Despite important variability in our dataset, we found latitudinal differences in the effect of litter functional diversity on decomposition, which we explained as evolutionary adaptations of litter-consuming detritivores to resource availability. Specifically, a balanced diet effect appears to operate at lower latitudes versus a resource concentration effect at higher latitudes. The latitudinal pattern indicates that loss of plant functional diversity will have different consequences on carbon fluxes across the globe, with greater repercussions likely at low latitudes

The effects of in-stream structure placements on a macroinvertebrate community : testing of reach-scale responses and mechanisms with regard to flow refugia

The effects of placements of in-stream structures on a macroinvertebrate community were examined in Spring Creek, a second-order stream of British Columbia, Canada. I tested the responses of organic matter and macroinvertebrates to structural changes at two spatial scales: reach-scale responses to the placements of boulder clusters; and the mechanisms through which in-stream structure affects macroinvertebrates as flow refugia at a microhabitat scale. The reach-scale study was conducted in three sections (length 40-56 m) within a 300-m reach with at least 20 m buffers between them. Two upstream reference sections were in relatively natural condition with channel meanders and abundant woody debris whereas the downstream treatment section had a relatively straight stream channel with less woody debris. In the treatment section, 6 boulder clusters were installed to manipulate habitat heterogeneity. These three sections were studied for three months prior to and 1.2 year following the placements of boulder clusters. Mean (140 %) and coefficient of variation (115 %) of velocity increased in the treatment section whereas the reference section remained relatively unchanged after the treatment. Through the increased organic matter storage (550 %), total macroinvertebrate abundance, which was dominated by detritus feeders, increased (280 %) in the treatment section to become similar in level to that in the reference sections almost one year after that treatment. However, the effect of placements of boulder clusters on taxonomic richness was negligible. Effects of food resource values on macroinvertebrate colonization of flow refugia during floods were examined in the downstream 180-m reach during three floods in 1999 and 2000. Substrate cages were used as an experimental unit, and were assigned to combinations of three types of treatments: food (natural or artificial leaves); flow refugia (reduced velocity or exposed); and flood (retrieval before or after a flood). Low and stable antecedent flow conditions resulted in significant responses of animals to the flood whereas high and variable antecedent flow resulted in little response. During the flood with the highest peak discharge observed among the three trials, two detritivorous taxa Paraleptophlebia and Despaxia accumulated in refugia and their colonization was disproportionally higher in the cage provided with high food resource value (natural leaves). Nevertheless, the accumulation of macroinvertebrates in flow refugia was species-specific, and was not consistent across the community. It was concluded that instream structures (boulder clusters) could be used as a remedy to restore macroinvertebrate community productivity.Forestry, Faculty ofGraduat

Freshwater biodiversity in human-dominated landscapes: Introduction

Worldwide, humans have converted natural wetlands into agricultural areas because of increasing demands for food. Rice paddy fields, farm ponds, fish ponds and irrigation and drainage ditches are typical landscape sectors in rural areas of Monsoon Asia and some parts of Europe and the Americas. Such habitats provide surrogate habitats for a range of aquatic wildlife that once inhabited natural wetlands (Elphick 2000; Lawler 2001). Traditionally, scientists and policy makers have largely focused on designating relatively pristine areas as protected areas for biodiversity conservation. Although zoning or land sparing may be effective especially where large areas of natural habitats remain, in recent decades equal attention has been given to land sharing, in which biodiversity conservation and human use of natural resources are simultaneously promoted in the same area (Fischer et al. 2008). Both land sharing and land sparing have complementary roles in maintaining biodiversity and ecosystem services. The concept of land sharing is not new, because all over the world people in rural areas have maintained and utilized natural resources for centuries. Specifically

Stream Resource Gradients Drive Consumption Rates of Supplemental Prey in the Adjacent Riparian Zone

Decades of research have revealed the crucial roles of cross-system energy flows (spatial subsidies) in mediating trophic interactions in recipient systems. Food web theory predicts that the responses of subsidized consumers are a key to understanding the net impacts of spatial subsidies on in situ prey/resources of recipient systems. However, less is known about the factors triggering the cascading biotic interactions across coupled ecosystems. Here, we quantify how riverine productivity (donor system) mediates terrestrial food web interactions through spatial subsidies to simplified gravel bar communities. Our comparative study in Japan indicated that higher algal biomass in aquatic systems led to increased supplies of emerging aquatic insects, which were associated with greater densities of terrestrial consumers (Carabid beetles) and enhanced consumption rates of supplemental in situ prey on gravel bars. Our results highlight the potential of donor productivity to drive cascading biotic interactions across coupled ecosystems. Because cross-system energy flows should originate, at least in part, from primary producers of donor systems, our fundamental finding may form the basis of future studies exploring the driving factors of cross-system trophic interactions

Exceptional color preferences for flying adult aquatic insects

This study tested the hypothesis that color affects the behavior of Ephemeroptera, Plecoptera, and Trichoptera (EPT) adults in the riparian zone of a gravel-bed river in northern Japan. EPT abundance was measured using plot scale surveys and a color-choice experiment that utilized non-shiny sticky traps in two contrasting colors, yellow and blue. Chloroperlidae and Hydrobiosidae were caught more abundantly in yellow and blue traps, respectively, whereas other taxa exhibited little or no color-affected responses. We proposed that Chloroperlidae responses were driven by relatively strong diurnal activity compared with those of other taxa. Hydrobiosidae's preference of blue remained unknown. Understanding the evolutionary background of color preferences in relation to other possibly interfering factors, such as reflection-polarization characteristics, at the species level will help advance the visual sensory ecology of aquatic insects

Testing local adaptations of affiliate freshwater pearl mussel, Margaritifera laevis, to its host fish, Oncorhynchus masou masou

Understanding the limiting factors of the reproduction process in host-affiliate relationships is a high priority. We examined the effects of habitat location on the reproductive process of freshwater pearl mussels Margaritifera laevis (Bivalvia, Unionida) as a parasite using sympatric and allopatric Oncorhynchus masou masou (Actinopterygii, Salmoniformes) as a host fish. Initial infection rates of parasitic larvae (glochidia) and transformation rates to cysts (encysted glochidia) were examined for all parasite-host combinations from three habitat locations (a total of nine combinations) to test the hypothesis that sympatric pairs of mussels and fish result in the highest success rates of glochidia infection and encystment. Measurements of glochidia-infected fish reared in flow-through experimental indoor tanks were taken at the initial infection point as well as at encystment, 2 weeks after the infection. Results disagreed with our hypothesis. Instead, an unexpected heterogeneity in a pathological deformity in gills explained a greater amount of variance in these processes. This deformity was responsible for reducing the initial infection rate and increasing the metamorphosis rates of initially attached glochidia to cysts. The field-measured prevalence of the gill deformity was low in all habitat locations, indicating that the deformity occurred during the acclimation period before infection for relatively small-sized host fish more susceptible to infection. Our results did not show the local adaptation of parasitic freshwater mussels to host fish but shed light on one of the least studied factors, providing an empirical underpinning of the importance of pathologically diversified host conditions in the reproductive processes of unionid mussels