Macroinvertebrate Biomass Research Articles

Above- and Below-ground Cascading Effects of Wild Ungulates in Temperate Forests

Ungulates have become abundant in many temperate forests, shifting tree species composition by browsing and altering soil physical conditions by trampling. Whether these effects cascade down to other trophic levels and ecosystem processes is poorly understood. Here, we assess the paths through which ungulates have cascading effects on other trophic levels (regeneration, litter, invertebrates, rodents and organic matter decomposition). We compared ungulate effects by comparing 15 response variables related to different trophic levels between paired fenced and unfenced plots in twelve temperate forest sites across the Netherlands, and used pathway analysis model to identify the (in)direct pathways through which ungulates have influenced these variables. We found that plots with ungulates (that is, unfenced) compared to plots without (that is, fenced) had lower litter depth, sapling diversity, sapling density, rodent activity, macro-invertebrate biomass, decomposition rate of tea bags, pine and birch litter and higher soil compaction. These findings were used in a path analysis to establish potential causal relationships, which showed that ungulate presence: decreased sapling density, which indirectly decreased rodent activity; decreased litter depth, which indirectly reduced invertebrate diversity; increased soil compaction, which also decreased invertebrate diversity. Soil pH decreased invertebrate biomass, which also increased nitrogen mineralization. Yet, we did not find cascading effects of ungulates on decomposition rates. Importantly, an increase in ungulate abundance strengthens the cascading effects in this system. Our results suggest that ungulates can trigger cascading effects on lower trophic levels, yet decomposition and mineralization rates are resilient to ungulate browsing and trampling. Therefore, temperate forests conservation could benefit by limiting ungulate abundance.

Factors contributing to leaf decomposition vary with temperature in two montane rivers of the Intermountain West, Utah

Terrestrial organic matter (OM) is an essential energy source that fuels many food webs. The factors contributing to OM decomposition and the rate at which OM decomposes can influence carbon fluxes through ecosystems. Previous research demonstrates that the factors driving OM decomposition can vary with environmental condition, prompting more research that characterizes the relative importance of each factor driving OM decomposition under differing environmental conditions. This is especially important for ecosystems that may be particularly vulnerable to climate change, like temperate, montane ecosystems. We used a 126-day leaf-pack study to compare and identify the most important factors (i.e., physical abrasion, microbial activity, and shredding macroinvertebrates) regulating OM decomposition rates (k) in two montane rivers. We used a structural equation model (SEM) to evaluate the relative importance of each factor contributing to OM decomposition. We found that k were significantly faster in the Blacksmith Fork. But when temperature differences were accounted for, k were approximately 1.5 times faster in the Logan River. Macroinvertebrate abundance and biomass, physical abrasion, nutrients, and temperature were significantly greater in the Blacksmith Fork, while microbial activity was the only factor significantly greater in the Logan River. We estimated that by day 100, microbes contributed 2.1 times more to decomposition in the Logan River (0.88 g; 14.6%) compared to the Blacksmith Fork (0.41 g; 6.9%). Relative to shredders (0.39 g; 6.5%), microbial contributions were approximately 2.2 times greater in the Logan River by day 100. Our SEM also revealed that microbes were more important to decomposition in this system relative to shredding macroinvertebrates. The reversal of k when day was replaced with degree-day and the significant direct effect of degree-days in our SEM suggests that temperature is a key factor regulating OM decomposition in these montane rivers. These findings contrast with many other studies conducted in montane systems, showing that microbes are less important contributors to OM decomposition at higher elevations, and further demonstrate that the relative importance of the factors driving OM decomposition is highly context dependent, even across small geographic scales.

A small omnivorous bitterling fish (Acheilognathus macropterus) facilitates dominance of cyanobacteria, rotifers and Limnodrilus in an outdoor mesocosm experiment.

Small omnivorous fish often dominate in subtropical shallow lakes, and they may affect the community structure of aquatic organisms on at least two trophic levels. However, in the study of aquatic food webs in subtropical lakes, most ecologists have focused on the effects of large-sized omnivorous species (e.g. common carp), studies of small-sized species being scarce. We conducted a mesocosm experiment with two treatments (fish presence and absence) to examine the effects of a small-sized omnivore, bitterling (Acheilognathus macropterus), on phytoplankton, zooplankton and benthic macroinvertebrates. Our results showed that bitterling presence significantly increased the chlorophyll a concentration and biomass of phytoplankton, which became dominated by cyanobacteria (mainly Aphanizomenon spp.) that accounted for >99% of both total phytoplankton abundance and biomass. Both the abundance and biomass of zooplankton were also higher in the fish-present treatment, but small rotifers became dominant, and the zooplankton:phytoplankton biomass ratio decreased, indicating less grazing on phytoplankton. Moreover, both the abundance and biomass of benthic macroinvertebrates (tubificids) were higher in the bitterling-present treatment than in the controls, which is opposite to the situation found when omni-benthivorous fish (e.g. crucian carp) dominate. Higher biomass of tubificids may, in turn, result in higher sediment nutrient release. Our study suggests that A. macropterus, and maybe also other bitterling species, can alter both pelagic and benthic assemblages via both top-down and bottom-up control effects and lead to more turbid water in eutrophic lakes. Thus, more attention should be paid to these small omnivorous species in the restoration and management of shallow subtropical lakes.

An integrative perspective to understand the impact of co-occurring ecosystem engineers on macroinvertebrates

Invasion of habitat-modifying nonnative species and alteration of ecosystem engineer by exploitation are two of the dominant human impacts on natural ecosystem functioning. The effects of these co-occurring ecosystem engineers may act simultaneously and vary independently depending on ambient environmental conditions they modify. Using a saltmarsh ecosystem with continuing invasion of nonnative cordgrass and aggregation of native bivalve shells, we tested whether the ecosystem engineering effects of shell aggregation on macroinvertebrates depended on the plants due to their ability to trap shell debris. We found habitats covered with shell aggregation and vegetated cordgrass significantly increase the biodiversity but decrease the biomass of macroinvertebrates comparing to the tidal bare flats, whereas no differences were detected among shell covered, cordgrass vegetated and their coexistent habitats. Our study highlights the importance of considering multiple, potentially conflicting management goals, which may require flexibility and trade-offs to integrate nonnative and native resources into ecosystem management.

Energía calórica, biomasa y estructura de los macroinvertebrados acuáticos en la reserva La Nitrera, Concordia, Antioquia, Colombia

El embalse La Nitrera se encuentra localizado a 2140 m.s.n.m. en el municipio de Concordia, departamento de Antioquia (Colombia) y es la única fuente de abastecimiento de agua del municipio. La operación de un embalse sobre un sistema lótico afecta la estructura y ensamblaje de sus ecosistemas acuáticos. Esta investigación tuvo como propósito analizar la distribución de la biomasa de los macroinvertebrados acuáticos antes y después del embalse, con el fin de determinar el impacto de este sobre las comunidades hidrobiológicas. Para tal fin, se analizaron las variables hidrobiológicas en época seca, de lluvia y en diferentes periodos de transición entre el año 2016 y 2017. Se investigaron cuatro estaciones de monitoreo, realizando la determinación, conteo y definiendo el rol trófico de los macroinvertebrados acuáticos, además de un análisis termogravimétrico (TGA) de la biomasa. Con la información obtenida, se construyó un modelo trófico y se calculó la pérdida de energía calórica disponible de la biomasa (TGA). Los resultados evidenciaron que las comunidades de macroinvertebrados acuáticos presentan una modularidad similar entre ellas en las estaciones antes del embalse, y una modularidad diferente en la estación después del embalse. A través del índice de modularidad (modelo Ghepi) y el análisis TGA, se logró establecer que el embalse altera la cadena trófica de las comunidades de macroinvertebrados acuáticos.

Structure of macroinvertebrate communities and bioassessment of water quality in the Weihe River mainstream and its typical tributaries from the northern Qinling Mountains

为摸清渭河干流及源于秦岭北麓典型支流的大型底栖动物群落特征，本研究于2017年10月和2018年5月对渭河干流及秦岭北麓5条典型支流共40个样点的大型底栖动物进行调查，并利用Margalef丰富度指数和生物指数BI生物指数对河流水质进行评价.共鉴定大型底栖动物210种，属于5门8纲75科187属.水生昆虫为优势类群，其物种数占总物种数的89.0%，且四节蜉属一种（Baetis sp.）作为绝对优势的物种出现在所有调查河流中.源于秦岭北麓的支流石头河底栖动物总密度最高（616.3 ind./m²），总生物量最大（5.265 g/m²）；而渭河干流底栖动物总密度最低（125.6 ind./m²），总生物量最小（0.289 g/m²）.水质较好的秦岭北麓典型支流底栖动物的Shannon-Wiener多样性指数、Margalef丰富度指数显著高于渭河干流，而Pielou均匀度指数在干支流间的差异性不大.通过Pearson相关分析和多元逐步回归分析得出，淤泥型底质、电导率、pH和硝酸盐氮是影响调查河流底栖动物群落特征的主导因子.丰富度指数法和生物指数法水质评价结果分别显示，渭河干流有73.3%和80.0%的采样点呈中度-重度污染状态，秦岭北麓典型支流有80.0%和68.0%的采样点呈无污染-轻度污染状态.本研究可为渭河流域生态管理与保护提供基础的数据支撑.;For exploring the macroinvertebrate community characteristics of the Weihe River mainstream and its typical tributaries originating from the northern Qinling Mountains, investigation of water environment and macroinvertebrates was conducted in 40 sampling sites in October 2017 and May 2018. Furthermore, Margalef richness and biological index (BI) biological indices were used to assess the water quality of studied rivers. Altogether 210 macroinvertebrates species were identified, belonging to 187 genera, 75 families, 8 classes and 5 phyla. Aquatic insects were the dominant group, accounting for 89.0% of the total species number, and the Baetis sp. was the dominant species in all studied rivers. The tributary Shitou River, had the highest values of total density(616.3 ind./m²), and the highest total biomass(5.265 g/m²). Whereas the total density (125.6 ind./m²) and total biomass (0.289 g/m²) of macroinvertebrates were both lowest in the Weihe River mainstream. The Shannon-Wiener diversity index(H')and Margalef richness index(R)of five typical tributaries were characterized by good water quality and significantly higher than those of the Weihe River mainstream, whereas the Pielou evenness index(J)showed insignificant difference between mainstream and tributaries. Pearson correlation analysis and the multiple linear regression analysis showed that “Silt plus clay” type substrate, conductivity, pH and nitrate nitrogen were the primary environment factors effecting the macroinvertebrate community characteristics in studied rivers. According to the water quality evaluation results of the richness index and the BI method, 73.3% and 80.0% of the mainstream sites were identified as moderately to heavily polluted, but 80.0% and 68.0% of tributary sites were identified as non-polluted to slightly polluted. This study can provide basic data supports for ecological management and protection in the Weihe River Basin.

Can nutrient additions facilitate recovery of Pacific salmon?

Multiple restoration actions have been implemented in response to declining salmon populations. Among these is the addition of salmon carcasses or artificial nutrients to mimic marine-derived nutrients historically provided by large spawning runs of salmon. A key assumption in this approach is that increased nutrients will catalyze salmon population growth. Although effects on aquatic ecosystems have been observed during treatments, it is unclear whether permanent population increases for salmon will occur. To test this assumption and address associated uncertainties, we linked a food web model with a salmon life cycle model to examine whether carcass additions in a river reach would improve conditions for salmon in the long term. Model results confirmed immediate increases in the biomass of periphyton, macroinvertebrates, and fish during carcass additions. In turn, juvenile salmon grew larger and experienced improved freshwater and smolt survival, which translated to a greater number of adults returning to spawn. However, once additions ceased, salmon abundance returned to pretreatment levels, which, based on our model, is owing to a combination of instream and out-of-basin factors. Overall, results of this work suggest that benefits during carcass and nutrient additions may not translate into persistent productivity of salmon unless additions are sustained indefinitely or other limiting factors are addressed.

The key role of increased fine sediment loading in shaping macroinvertebrate communities along a multiple stressor gradient in a Eurasian steppe river (Kharaa River, Mongolia)

AbstractAquatic communities across the Eurasian steppe face increasing anthropogenic pressures due to rapid population growth, catchment‐wide land‐use changes, and climate change. The particular type, intensity, overlay, and legacy of impacts along longitudinal gradients of Eurasian river networks provide a unique setting to investigate ecological responses in identifiable multiple stressor environments. We studied macroinvertebrate communities along the Kharaa River, Mongolia, which display a distinct, downstream gradient of moderate nutrient enrichment, disturbed bank morphology, reduced riparian vegetation, elevated turbidity, increased fine sediment substrate proportions, and fine sediment intrusion into the hyporheic zone. Within the encountered ranges of physical and chemical environmental factors (TP 0.02–0.09 mg/L, TN 0.33–0.96 mg/L, conductivity 167–322 µS/cm, formazin nephelometric units 0.62–5.43) and hyporheic fine sediment intrusion (0.9–1.6 g dry weight [DW]·L−1·day−1) the population densities and biomass of macroinvertebrates were high (5,313 ± 410 individuals/m2 and 2,656 ± 152 mg DW/m2) and notably stable. In contrast, macroinvertebrate community structure showed strong and statistically significant negative linear relationships (Pearson's r) with turbidity, that is, for taxa richness (r = −.83), Shannon index of diversity (r = −.89), Evenness (r = −.86), the relative abundance of Ephemeroptera, Plecoptera, and Trichoptera (EPT) individuals (r = −.93) and relative biomass of hard substrate colonizers (r = −.86). The relative biomasses of fine substrate colonizers, as well as Chironomidae and Oligochaeta (both r = .76), were positively correlated with mean turbidity values. In addition, the Proportion of Sediment‐sensitive Invertebrates (PSI) methodology was adjusted for local application and the resulting index scores followed a similar pattern, with PSI also being significantly correlated (r = .66) with the relative abundance of EPT individuals, the latter being the most sensitive macroinvertebrate community index. We conclude that fine sediment load is the key factor for shaping macroinvertebrate community structure in the multistressor setting of the Kharaa River followed by hydromorphological habitat complexity determined by shear stress, substrate, and grain size distributions. We suggest that the implementation of effective regional management strategies aiming at the reduction of fine sediment pollution should be given the highest priority.

CHARACTERIZATION OF THE BIOTIC (MACROPHYTES AND MACROINVERTEBRATES) AND ABIOTIC FACTORS OF PANTANAL PONDS IN THE MIRANDA RIVER FLOODPLAIN

The Pantanal has an exuberant biodiversity that is constantly regulated by the dynamics of the climate and by the flood pulses. The objective of this work was to characterize and evaluate the biotic (macrophytes and macroinvertebrates) and abiotic factors (pH, temperature, dissolved oxygen, conductivity, total dissolved solids, water turbidity, chlorophyll a and pheophytin-a) of Pantanal ponds depending on the dry or rainy season. Therefore, five ponds with different characteristics were analyzed and five samples of water were collected during the dry and rainy season. For sampling of the macrophytes and collection of the macroinvertebrates we used hand nets (area of 0,09m2, opening of 5000 μm). This was done in order to observe seasonal difference in pH, chlorophyll-a and pheophytin-a and spatial differences between dissolved oxygen, electrical conductivity, turbidity, chlorophyll a and pheophytin-a was observed. The aquatic macrophyte Eichornia azurea ( Commelinales, Ponteridaceae) showed high dominance and relative vegetation cover in at least three ponds, which was also related to higher values of macroinvertebrate biomass. On the other hand, the ponds that presented low dominance or absence of E. azurea presented high diversity of aquatic macrophytes. However, these intrinsic biological characteristics of the ponds altogether with the abiotic parameters demonstrated that there are distinct patterns in the dynamics of these ecosystems during the drought and flood regimes.

Beavers alter stream macroinvertebrate communities in north‐eastern Utah

Abstract Understanding changes in macroinvertebrate communities is important because they play a large role in stream ecosystem functioning, and they are an important food resource for fish. Beaver‐induced changes to stream morphology could alter macroinvertebrate communities, which in turn could affect food webs and ecosystem function. However, studies investigating the effects of North American beaver activities on macroinvertebrates are rare in the inter‐mountain west, an area with high potential for beaver‐assisted restoration. The aim of this study was to quantify differences in the macroinvertebrate community between unaltered segments of streams and within beaver ponds in north‐eastern Utah, U.S.A. We assessed macroinvertebrate species richness, biomass, density, functional feeding group composition, mobility group composition, and macroinvertebrate habitat characteristics to test the hypothesis that macroinvertebrate communities will differ among habitat types (undammed stream segments and beaver ponds) in beaver‐occupied streams. Beaver pond communities significantly differed from lotic reach communities in many ways. Beaver ponds were less diverse with 25% fewer species. Although there was variability among streams, in general, beaver ponds had 75% fewer individuals and 90% lower total macroinvertebrate biomass compared to lotic reaches. Regarding functional feeding groups, beaver ponds contained more engulfers, while lotic reaches contained more scrapers, filterers, and gatherers. For mobility groups, beaver ponds had more sprawlers, while lotic reaches had more clingers. Swimmers were also more prevalent in lotic reaches, although this is probably due to the abundance of Baetis within lotic reaches. More beaver pond taxa were classified as lentic‐dwelling insects, while more lotic reach taxa were categorised as preferring lotic habitats. The creation of ponds by beavers fundamentally altered the macroinvertebrate community in north‐eastern Utah streams. Such changes to stream macroinvertebrate communities suggest that recolonisation of beavers across North America may be altering stream functioning and food webs. Our study highlights the need to further investigate the effects of beaver recolonisation on stream communities.

Relationships between soil macroinvertebrates and nonnative feral pigs (Sus scrofa) in Hawaiian tropical montane wet forests

Nonnative feral pigs (Sus scrofa) are recognized throughout the New World as a highly significant introduced species in terms of ecosystem alteration. Similarly, nonnative soil macroinvertebrates (e.g. earthworms, ground beetles) invade and alter the structure and function of native habitats globally. However, the relationship between feral pigs and soil macroinvertebrates remains largely unknown. This study analyzed relationships between these taxa using nine sites located inside and outside of feral pig management units representing a ~ 25 year chronosequence of removal in tropical montane wet forests in Hawai‘i. Soil macroinvertebrates were sampled from plots categorized as: actively trampled by feral pigs, actively rooted by feral pigs, feral pigs present with no signs of recent activity, or feral pigs removed over time. In total, we found 13 families of primarily nonnative soil macroinvertebrates. Plots with active trampling correlated with lower total macroinvertebrate abundance, biomass, and family richness. Plots with active rooting were correlated with higher abundance of nonnative earthworms (Lumbricidae and Megascolicidae) and ground beetles (Carabidae). The abundance, biomass, and biodiversity of macroinvertebrates did not vary with time since feral pig removal. Collectively, these results indicate: (1) trampling by feral pigs negatively influences soil macroinvertebrates; (2) feral pigs either modify habitats while rooting thereby facilitating earthworm and ground beetle habitat use or selectively seek out target prey species of soil macroinvertebrates; and (3) removal of feral pigs has minimal impacts on soil macroinvertebrates over time. These results are important globally due to the broadly overlapping ranges of S. scrofa and nonnative macroinvertebrates.

Simulating nutrient release from parental carcasses increases the growth, biomass and genetic diversity of juvenile Atlantic salmon

Abstract The net transport of nutrients by migratory fish from oceans to inland spawning areas has decreased due to population declines and migration barriers. Restoration of nutrients to increasingly oligotrophic upland streams (that were historically salmon spawning areas) have shown short‐term benefits for juvenile salmon, but the longer term consequences are little known. Here we simulated the deposition of a small number of adult Atlantic salmon Salmo salar carcasses at the end of the spawning period in five Scottish upland streams (‘high parental nutrient’ treatment), while leaving five reference streams without carcasses (‘low parental nutrient’ treatment). All streams received exactly the same number of salmon eggs (n = 3,000) drawn in equal number from the same 30 wild‐origin families, thereby controlling for initial egg density and genetic composition. We then monitored the resulting juvenile salmon and their macroinvertebrate prey, repeating the carcass addition treatment in the next spawning season. Macroinvertebrate biomass and abundance were five times higher in the high parental nutrient streams, even 1 year after the carcass addition, and led to faster growth of juvenile salmon over the next 2 years (but with no change in population density). This faster growth led to more fish exceeding the size threshold that would trigger emigration to sea at 2 rather than 3 years of age. There was also higher genetic diversity among surviving salmon in high parental nutrient streams; genotyping showed that these effects were not due to immigration but to differential survival. Synthesis and applications. This 2‐year field experiment shows that adding nutrients that simulate the presence of small numbers of adult salmon carcasses can have long‐term effects on the growth rate of juvenile salmon, likely increasing the number that will migrate to sea early and also increasing their genetic diversity. However, the feasibility of adding nutrients to spawning streams as a management tool to boost salmon populations will depend on whether the benefits at this stage are maintained over the entire life cycle.

Climate and fishing drive regime shifts in consumer-mediated nutrient cycling in kelp forests.

Globally, anthropogenic pressures are reducing the abundances of marine species and altering ecosystems through modification of trophic interactions. Yet, consumer declines also disrupt important bottom-up processes, like nutrient recycling, which are critical for ecosystem functioning. Consumer-mediated nutrient dynamics (CND) is now considered a major biogeochemical component of most ecosystems, but lacking long-term studies, it is difficult to predict how CND will respond to accelerating disturbances in the wake of global change. To aid such predictions, we coupled empirical ammonium excretion rates with an 18-year time series of the standing biomass of common benthic macroinvertebrates in southern California kelp forests. This time series of excretion rates encompassed an extended period of extreme ocean warming, disease outbreaks, and the abolishment of fishing at two of our study sites, allowing us to assess kelp forest CND across a wide range of environmental conditions. At their peak, reef invertebrates supplied an average of 18.3±3.0µmolNH4 + m-2 hr-1 to kelp forests when sea stars were regionally abundant, but dropped to 3.5±1.0µmolNH4 + m-2 hr-1 following their mass mortality due to disease during a prolonged period of extreme warming. However, a coincident increase in the abundance of the California spiny lobster, Palinurus interupptus (Randall, 1840), likely in response to both reduced fishing and a warmer ocean, compensated for much of the recycled ammonium lost to sea star mortality. Both lobsters and sea stars are widely recognized as key predators that can profoundly influence community structure in benthic marine systems. Our study is the first to demonstrate their importance in nutrient cycling, thus expanding their roles in the ecosystem. Climate change is increasing the frequency and severity of warming events, and rising human populations are intensifying fishing pressure in coastal ecosystems worldwide. Our study documents how these projected global changes can drive regime shifts in CND and fundamentally alter a critical ecosystem function.

Threatened habitat at Great Salt Lake: Importance of shallow-water and brackish habitats to Wilson’s and Red-necked phalaropes

Abstract Great Salt Lake (GSL) is the largest hypersaline lake in North America and is the fall staging area for a high proportion of North America’s Wilson’s Phalaropes (Phalaropus tricolor) and Red-necked Phalaropes (Phalaropus lobatus). Unfortunately, diversion of freshwater for agriculture and development has decreased the size of GSL by 48%. To assess the potential impact of a smaller GSL on phalaropes, we collected data from 2013 to 2015 from sites where large, dense flocks of phalaropes congregated and sites where there were no phalaropes. At each site, we measured the densities of invertebrates that were preyed upon by phalaropes, including larval and adult brine flies (Ephydridae), adult brine shrimp (Artemia franciscana), chironomid larvae (Chironomidae), and corixid adults (Corixidae). Abiotic characteristics measured included water depth, water salinity, water temperature, wind speed, and benthic substrate. We analyzed high-salinity sites separately from low-salinity sites because they contained different invertebrates. High-salinity sites were in Carrington and Gilbert bays and were relatively deep (mostly <2 m). At the high-salinity sites, phalaropes exhibited a preference for sites with an abundance of adult brine flies and for microbialite substrates. The low-salinity sites were in Ogden and Farmington bays and were shallow (<1 m). At low-salinity sites, large phalarope flocks were more likely to occur at sites that were shallower, less saline, and had a high biomass of benthic macroinvertebrates. Our results indicate that physical features and prey availability are both important in determining phalarope habitat use at GSL. Phalaropes prefer to use shallower parts of GSL and brackish waters. These areas will be especially impacted by decreased freshwater inflow into GSL.

Riverscape genetic variation, migration patterns, and morphological variation of the threatened Round Rocksnail, Leptoxis ampla.

Within riverine systems, headwater populations are hypothesized to harbour higher amounts of genetic distinctiveness than populations in the main stem of a river and display increased genetic diversity in large, downstream habitats. However, these hypotheses were mostly developed with insects and fish, and they have not been tested on many invertebrate lineages. Pleuroceridae gastropods are of particular ecological importance to rivers of eastern North America, sometimes comprising over 90% of macroinvertebrate biomass. Yet, virtually nothing is known of pleurocerid landscape genetics, including whether genetic diversity follows predictions made by hypotheses developed on more mobile species. Moreover, the commonly repeated hypothesis that intraspecific morphological variation in gastropods results from ecophenotypic plasticity has not been well tested on pleurocerids. Using 2bRAD-seq to discover single nucleotide polymorphisms, we show that the threatened, Cahaba River endemic pleurocerid, Leptoxis ampla, has limited gene flow among populations and that migration is downstream-biased, conflicting with previous hypotheses. Both tributary and main stem populations harbour unique genomic profiles, and genetic diversity was highest in downstream populations. Furthermore, L.ampla shell morphology was more correlated with genetic differences among individuals and populations than habitat characteristics. We anticipate similar genetic and demographic patterns to be seen in other pleurocerids, and hypotheses about gene flow and population demographics that were based on more mobile taxa often, but not always, apply to freshwater gastropods. From a conservation standpoint, genetic structure of L.ampla populations suggests distinctive genetic diversity is lost with localized extirpation, a phenomenon common across the range of Pleuroceridae.

Using stable isotope approach to quantify pond dam impacts on isotopic niches and assimilation of resources by invertebrates in temporary streams: a case study

Fishponds built across streams can greatly affect their functioning, especially through loss of ecological continuity but also changes in water availability and trophic resources. Yet, their consequences on communities and stream functioning remain largely understudied. We investigated effects of fishpond dams on the trophic ecology of macroinvertebrate communities in temporary low-order streams using C and N stable isotopes. Food resources and macroinvertebrates were sampled in one upstream and one downstream site of two temporary streams, one stream without (reference stream) versus one with a fishpond (impacted stream) and used for isotopic analyses. Results suggested moderate effects of fishponds on the upstream tributaries. In contrast, at the downstream impacted site, ten times higher macroinvertebrate biomass and modifications in the trophic niches were recorded, likely due to changes in resource availability/quality and dam-related hydrology. By modifying the food sources as well as water fluxes, fishpond dams tend to alter macroinvertebrate communities but also shift the trophic dynamics downstream. This assessment stresses the need for exploring their impacts on food webs and nutrient fluxes at larger downstream distances to better understand their effects before drawing conclusions in regard to their management.

Evaluating ecosystem effects of climate change on tropical island streams using high spatial and temporal resolution sampling regimes.

Climate change is expected to alter precipitation patterns worldwide, which will affect streamflow in riverine ecosystems. It is vital to understand the impacts of projected flow variations, especially in tropical regions where the effects of climate change are expected to be one of the earliest to emerge. Space-for-time substitutions have been successful at predicting effects of climate change in terrestrial systems by using a spatial gradient to mimic the projected temporal change. However, concerns have been raised that the spatial variability in these models might not reflect the temporal variability. We utilized a well-constrained rainfall gradient on Hawaii Island to determine (a) how predicted decreases in flow and increases in flow variability affect stream food resources and consumers and (b) if using a high temporal (monthly, four streams) or a high spatial (annual, eight streams) resolution sampling scheme would alter the results of a space-for-time substitution. Declines in benthic and suspended resource quantity (10- to 40-fold) and quality (shift from macrophyte to leaf litter dominated) contributed to 35-fold decreases in macroinvertebrate biomass with predicted changes in the magnitude and variability in the flow. Invertebrate composition switched from caddisflies and damselflies to taxa with faster turnover rates (mosquitoes, copepods). Changes in resource and consumer composition patterns were stronger with high temporal resolution sampling. However, trends and ranges of results did not differ between the two sampling regimes, indicating that a suitable, well-constrained spatial gradient is an appropriate tool for examining temporal change. Our study is the first to investigate resource to community wide effects of climate change on tropical streams on a spatial and temporal scale. We determined that predicted flow alterations would decrease stream resource and consumer quantity and quality, which can alter stream function, as well as biomass and habitat for freshwater, marine, and terrestrial consumers dependent on these resources.

Antagonistic effects of multiple stressors on macroinvertebrate biomass from a temperate estuary (Minho estuary, NW Iberian Peninsula)

An ecosystem model of the Minho estuary (NW coast of Iberian Peninsula) was implemented in AQUATOX 3.1 (US-EPA) to check whether the effects of temperature rise, dry years, rainy years and river flow decrease acting isolated (single stressor) or combined (multiple stressor) would induce the same type of response on macroinvertebrate biomass variation and to identify the type of stressor interactions. The model was parameterised with site-specific and species-specific data and accounts for a food web with primary producers, benthic invertebrates, fish and detritus, with 12 biotic groups, 4 groups of detritus and 12 forcing functions.Results showed that macroinvertebrate biomass responded differently to single stressor and multiple stressor scenarios and interactions among the tested stressors were antagonistic. During medium term simulations (∼6 years), the biomass of macroinvertebrate communities from the Minho estuary was maintained or slightly increased in single scenarios of temperature rise but the occurrence of antagonistic interactions between temperature rise, river flow decrease, dry years and rainy years counteracted the increasing tendency in multiple stressor scenarios.Overall, the present results highlight the strong dependence of the system’s biomass and production on hydrodynamics and contribute to increase knowledge on the mechanistic processes behind this. Thus, we recommend an ecosystem-based management of the Minho River basin supported by models such as the present one.

Macroinvertebrate communities characteristics and their responses to fluvial geomorphological feature of typical debris flow gullies in the Xiaojiang River Basin, Yunnan Province

云南小江流域为典型干热河谷区，该区域干热少雨，流域内泥石流沟众多，生态环境十分脆弱.2017年4月和9月对小江流域的吊嘎河、蒋家沟、蓝泥坪沟、清水沟、陶家小河5条泥石流沟及小江干流开展了系统调查，旨在摸清5条泥石流沟及小江干流河流地貌、水环境及底栖动物群落现状，分析不同河床结构发育程度的泥石流沟间的底栖动物群落差异，揭示底栖动物对反映河床结构发育程度的河流地貌特征参数凹凸度的响应关系.调查期间于5条泥石流沟及小江干流中共采集到底栖动物70种，隶属于4门6纲38科69属，其中环节动物6种，软体动物2种，节肢动物61种，扁形动物1种.从种类类群来看，5条泥石流沟及小江干流的底栖动物物种数、密度、生物量上均以节肢动物占绝对优势，分别占总量的78.0%~92.5%、98.7%~100%、65.0%~100%.从功能摄食类群上来看，5条泥石流沟及小江干流底栖动物密度上均以直接收集者为主，占总量的74.3%~96.3%.回归分析表明，5条泥石流沟中底栖动物物种数、密度及生物量均与河流地貌特征参数凹凸度呈正相关关系，由此可见，发育良好的河床结构在维持河流地貌稳定和改善河流生态方面起着举足轻重的作用.本研究结果可为小江流域山区河流泥石流沟河床结构重建及生态修复提供科学依据.;The Xiaojiang River Basin is a typical dry-hot valley area, characterized by high temperatures, little rain and many debris flow gullies, where ecological environment is very fragile. In April and September of 2017, field surveys were conducted in the five debris flow gullies (i.e., the Diaoga Creek, the Jiangjia Creek, the Lanniping Creek, the Qingshui Creek, and the Taojiaxiaohe Creek) and the Xiaojiang River. The purpose of this study is to understand fluvial geomorphological feature, water environment, and macroinvertebrate communities in the five debris flow gullies and the Xiaojiang River, to analyze the differences in macroinvertebrate communities among debris flow gullies with different riverbed structures, and to reveal the responses of macroinvertebrates to the fluvial geomorphological parameter (degree of concavity-convexity) reflecting the development degree of riverbed structure. A total of 70 taxa of macroinvertebrates were identified, belonging to 4 phyla, 6 classes, 38 families and 69 genera. With regard to the taxonomic groups, arthropods were dominant in the species richness, density, and biomass of macroinvertebrates in the five debris flow gullies and the Xiaojiang River, accounting for 78.0%-92.5%, 98.7%-100.0% and 65.0%-100.0% of the total richness, densities, and biomass, respectively. With regard to the functional feeding groups, collector-gatherers were all dominated in the five debris flow gullies and the Xiaojiang River, accounting for 74.3%-96.3% of the total densities. Regression analyses showed that the species number, density, and biomass of macroinvertebrates were all positively correlated with the fluvial geomorphological parameter (degree of concavity-convexity) of the five debris flow gullies. The present study indicated that the well-developed riverbed structure plays an important role in maintaining the stability of the fluvial geomorphology and ecological quality. The results of this study can provide scientific basis for riverbed structure reconstruction and ecological restoration of debris flow gullies in mountain regions of the Xiaojiang River Basin.

Effects of short-term hydrological processes on benthic macroinvertebrates in salt marshes: A case study in Yangtze Estuary, China

Understanding the effects of hydrological processes on the benthic macroinvertebrates in salt marshes can provide theoretical basis for species diversity restoration, coastal environment protection, and comprehensive exploitation and utilization of salt marsh ecosystems. In this study, 4 fixed-point sampling sites were set up in the salt marsh of the East Nanhui tidal flat in the Yangtze Estuary for benthic macroinvertebrate survey, hydrological monitoring and sedimentary parameter collection over two short-time scales (semidiurnal and fortnightly cycles). Based on the results of these surveys, we analyzed the effects of hydrological processes on the benthic macroinvertebrates over different timescales. The results showed that benthic macroinvertebrates assemblages varied significantly over the semidiurnal and fortnightly tide periods but not between sites. The number of species and the abundance of the benthic macroinvertebrates during spring tide period were significantly lower than that during neap tide period, although the biomass during both tidal periods were not significantly different. There was no significant variation in the number of species, abundance, and biomass of benthic macroinvertebrates over the semidiurnal tidal scale in general with few exceptions. However, there were significant differences in most of the hydrological and sedimentary parameters between the spring and neap tide periods, as well as between semidiurnal tides in these two periods. Two principal components, the intensity of hydrological processes (PC1) and the physicochemical properties of water and sediment (PC2), were derived from principal component analysis on hydrological factors and sedimentary physicochemical parameters. The results show that PC1 had a significant effect on abundance of benthic macroinvertebrate community; while PC2 had a significant effect on biomass. The best combined environmental factors, which exhibited significant correlations with the characteristics of the benthic macroinvertebrates and also their taxonomic classes, varied across the sampling periods. This study indicates that short-term hydrological processes can not only directly affect the benthic macroinvertebrates, but also indirectly affect the communities by altering sedimentary physicochemical factors. There were significant differences in the effects of the hydrological processes on the benthic macroinvertebrate community over the semidiurnal and fortnightly tidal scales, and it could be inferred that the scale effect still exists in the short-time scale.