Belinda Gallardo

Global ecological impacts of invasive species in aquatic ecosystems

The introduction of invasive species, which often differ functionally from the components of the recipient community, generates ecological impacts that propagate along the food web. This review aims to determine how consistent the impacts of aquatic invasions are across taxa and habitats. To that end, we present a global meta-analysis from 151 publications (733 cases), covering a wide range of invaders (primary producers, filter collectors, omnivores and predators), resident aquatic community components (macrophytes, phytoplankton, zooplankton, benthic invertebrates and fish) and habitats (rivers, lakes and estuaries). Our synthesis suggests a strong negative influence of invasive species on the abundance of aquatic communities, particularly macrophytes, zooplankton and fish. In contrast, there was no general evidence for a decrease in species diversity in invaded habitats, suggesting a time lag between rapid abundance changes and local extinctions. Invaded habitats showed increased water turbidity, nitrogen and organic matter concentration, which are related to the capacity of invaders to transform habitats and increase eutrophication. The expansion of invasive macrophytes caused the largest decrease in fish abundance, the filtering activity of filter collectors depleted planktonic communities, omnivores (including both facultative and obligate herbivores) were responsible for the greatest decline in macrophyte abundance, and benthic invertebrates were most negatively affected by the introduction of new predators. These impacts were relatively consistent across habitats and experimental approaches. Based on our results, we propose a framework of positive and negative links between invasive species at four trophic positions and the five different components of recipient communities. This framework incorporates both direct biotic interactions (predation, competition, grazing) and indirect changes to the water physicochemical conditions mediated by invaders (habitat alteration). Considering the strong trophic links that characterize aquatic ecosystems, this framework is relevant to anticipate the far-reaching consequences of biological invasions on the structure and functionality of aquatic ecosystems.

Macroinvertebrate patterns along environmental gradients and hydrological connectivity within a regulated river-floodplain

Abstract.Flood and flow pulses are primary factors that regulate macroinvertebrate community structure in river-floodplain ecosystems. In order to assess the impacts of these important hydrological events in a regulated Mediterranean river, bimonthly water and macroinvertebrate samples were collected in 2006 in the Middle Ebro River channel and six floodplain wetlands (NE Spain).We found significant differences among the river sites (permanently connected), two constructed wetlands (groundwater seepage) and three natural oxbow lakes (surface connected at 400, 800 and 1200 m3/s). River sites were dominated by aquatic worms (e.g., Naididae) and showed a high degree of eutrophication. Constructed wetlands provided new habitat for predatory insects (e.g.,Coenagrion scitulum and Trithemis annulata) that benefited from the absence of fish. Natural oxbow lakes were dominated by crustaceans (e.g., Atyaephyra desmarestii, Procambarus clarkii) and were highly overlapped in Correspondence Analysis. Canonical Correspondence Analysis, coupled with variance partitioning, showed that hydrological connectivity accounted for 28% of the variability in the invertebrate community, followed by physicochemical (10%) and trophic (7%) factors. Differences in frequency and duration of flood pulses in natural oxbow lakes were not enough to generate distinctive macroinvertebrate assemblages in the different wetlands. Analysis of variance showed that richness and total abundance increased with hydrological connectivity, while diversity showed a rather unimodal distribution. Generalized Additive Models indicated that among the measured environmental variables, nitrate concentration strongly affected the composition, abundance and diversity of aquatic communities. Our data indicate that increasing the diversity of water body types in degraded floodplains enhances biodiversity and aids in the functional and ecological recovery of the riverine landscape.

The Importance of the Human Footprint in Shaping the Global Distribution of Terrestrial, Freshwater and Marine Invaders

Human activities such as transport, trade and tourism are likely to influence the spatial distribution of non-native species and yet, Species Distribution Models (SDMs) that aim to predict the future broad scale distribution of invaders often rely on environmental (e.g. climatic) information only. This study investigates if and to what extent do human activities that directly or indirectly influence nature (hereafter the human footprint) affect the global distribution of invasive species in terrestrial, freshwater and marine ecosystems. We selected 72 species including terrestrial plants, terrestrial animals, freshwater and marine invasive species of concern in a focus area located in NW Europe (encompassing Great Britain, France, The Netherlands and Belgium). Species Distribution Models were calibrated with the global occurrence of species and a set of high-resolution (9×9 km) environmental (e.g. topography, climate, geology) layers and human footprint proxies (e.g. the human influence index, population density, road proximity). Our analyses suggest that the global occurrence of a wide range of invaders is primarily limited by climate. Temperature tolerance was the most important factor and explained on average 42% of species distribution. Nevertheless, factors related to the human footprint explained a substantial amount (23% on average) of species distributions. When global models were projected into the focus area, spatial predictions integrating the human footprint featured the highest cumulative risk scores close to transport networks (proxy for invasion pathways) and in habitats with a high human influence index (proxy for propagule pressure). We conclude that human related information–currently available in the form of easily accessible maps and databases—should be routinely implemented into predictive frameworks to inform upon policies to prevent and manage invasions. Otherwise we might be seriously underestimating the species and areas under highest risk of future invasions.

Effects of hydrological connectivity on the substrate and understory structure of riparian wetlands in the Middle Ebro River (NE Spain): Implications for restoration and management

Abstract.The hydroperiod, flooded sediments and riparian understory were examined for eight riparian wetlands of one Ebro River reach (NE Spain) to relate river-floodplain interactions at different spatio-temporal scales with wetland strucuture. This analysis served as a basis for assessing the ecological status of the study reach and proposing a valid restoration plan. A comparison of water-level fluctuations in riparian wetlands with that in the river channel during an ordinary flood was use to characterize the hydroperiod. This characterization was further linked with the results of a multivariate analysis performed using sediment physico-chemistry. Moreover, different measures of understory diversity were used to estimate the successional stage of eight riparian wetlands located in the same reach of the Ebro River. We described four hydroperiod types from the examined flood, from disconnected oxbow lakes to backflow channels fluctuating in concert with the Ebro River. Also three types of sediment differ in their organic matter content. Both results were closely related reflecting the dominance of endogenous or allogeneous processes. However, such heterogeneity was interpreted as being variable over longer spatiotemporal scales. In addition, the riverscape was found to be homogenous and dominated by wetlands at mature successional stages. Consequently, the lack of erosive floods within the reach seems to make inclusion of ecological restoration of geomorphological dynamics a highly appropriate management objective. Alternative strategies at both reach and site scales are proposed.

The effect of anthropogenic disturbance on the hydrochemical characteristics of riparian wetlands at the Middle Ebro River (NE Spain)

In natural systems, the chemistry of floodplain waters is a function of the source of the water, which is influenced by geomorphic features of riparian wetlands. However, anthropogenic disturbances may alter both geomorphic features and the natural balance of water mixing in the floodplain. The aim of this study was to classify riparian wetlands and characterize their water characteristics in one reach of the Middle Ebro River to assess the hydrochemical functioning of the system. In order to accomplish that goal, water samples were collected at 40 sampling sites during low-water conditions and two floods of different magnitude. Moreover, geomorphic characteristics of riparian wetlands were also analyzed to interpret the results at broader spatio-temporal scales. Three group of wetlands were identified using multivariate ordination: (1) major and secondary channels highly connected to the river by surface water, containing weakly ionized water with high nitrate levels during floods; (2) secondary channels and artificial ponds located in riparian forests near the river, most of which were affected by river seepage during the examined events. This type of sites had high major ions concentrations and elevated spatial variability with respect to nutrient concentrations during floods; (3) Siltated oxbow lakes, whose hydrogeochemical features seemed to be unaffected by factors related to river fluctuations. Total dissolved solids, major ion (sulfate, chloride, sodium, calcium, magnesium, and potassium) and nutrient (nitrate, ammonium and organic nitrogen, and phosphate) depended upon the relationships between surface and subsurface water flows. Seasonal changes and geomorphic characterization indicated that a strong functional dependence of floodplain wetlands close to the main river channel is established, whereas most of the floodplain area remains disconnected from river dynamics. Moreover, the effect of nitrate-enriched agricultural runoff seems to affect water quality and hydrochemical gradients of the system. Based on our results, we propose different types of actions for the management of the Ebro River flow to ensure a more natural ecological functioning of its floodplains.

Wetland Restoration: Integrating Scientific-Technical, Economic, and Social Perspectives

ECOLOGICAL RESTORATION 23:3 ■ SEPTEMBER 2005 Ecological Restoration, Vol. 23, No. 3, 2005 ISSN 1522-4740 E-ISSN 1543-4079 ©2005 by the Board of Regents of the University of Wisconsin System. Wetlands are being restored around the world using a wide spectrum of different approaches from the application of well-grounded scientific knowledge to obtain a precise objective to trial-and-error practices just to have water for some time on a piece of land. Whatever the methodology, wetland restoration projects can provide good theoretical and practical knowledge because, compared to other ecosystems, wetland ecosystems react relatively soon to manipulations (Mitsch and Gosselink 2000, Zentner and others 2003). Given this range of approaches, it must also be noted that the success of an ecological restoration project depends on many factors that should be taken into account when planning and developing a project. These can be grouped into three types: 1) technical failures or lack of scientific information, 2) economic constraints, and 3) social disagreements. The integration of these three perspectives— scientific-technical, economic and social —is important to obtain all the values of an ecological restoration project (Comín 2002, Winterhalder and others 2004). In this article, we present a number of wetland restoration experiences developed under different conditions in northeastern Spain in order to look for common recommendations for planning future, highvalue projects.

Europe’s top 10 invasive species: relative importance of climatic, habitat and socio-economic factors

Using a representative set of 10 of the worst invasive species in Europe, this study investigates the relative importance of climatic, habitat and socio-economic factors in driving the occurrence of invasive species. According to the regression models performed, these factors can be interpreted as multi-scale filters that determine the occurrence of invasive species, with human degradation potentially affecting the performance of the other two environmental filters. Amongst climate factors, minimum temperature of the coldest month was one of the most important drivers of the occurrence of Europe’s worst freshwater and terrestrial invaders like the red swamp crayfish (Procambarus clarkii), Bermuda buttercup (Oxalis pes-caprae) and Sika deer (Cervus nippon). Water chemistry (alkalinity, pH, nitrate) determines the availability of habitat and resources for species at regional to local levels and was relevant to explain the occurrence of aquatic and semi-aquatic invaders such as the brook trout (Salvalinus fontinallis) and Canada goose (Branta canadensis). Likewise, nitrate and cholorophyll-a concentration were important determinants of marine invaders like the bay barnacle (Balanus improvisus) and green sea fingers (Codium fragile). Most relevant socio-economic predictors included the density of roads, country gross domestic product (GDP), distance to ports and the degree of human influence on ecosystems. These variables were particularly relevant to explain the occurrence of the zebra mussel (Dreissena polymorpha) and coypu (Myocastor coypu), species usually associated to disturbed environments. The Japanese kelp (Undaria pinnatifida) was generally distributed much closer to ports than the other two marine organisms, although insufficient information on human impacts prevented a correct assessment of the three marine species. In conclusion, this study shows how socio-economic development is associated with the presence of the top 10 worst European invasive species at a continental scale, and relates this fact to the provision and transport of propagules and the degradation of natural habitats that favour the establishment of invasive species.

Trans-national horizon scanning for invasive non-native species: a case study in western Europe

Horizon scanning for high-risk invasive non-native species (INNS) is crucial in preparing and implementing measures to prevent introductions, as well as to focus efforts in the control of species already present. We initiated a trans-national horizon-scanning exercise focused on four countries in western Europe: Great Britain, France, Belgium and The Netherlands, which share similar environmental and socio-economic characteristics. We followed a structured four-step approach combining existing knowledge about INNS, with a collaborative identification of priorities for research and management: (1) systematic review of potential INNS of concern, (2) discrimination of INNS into an Alert and Black List depending on their absence or presence in the study area respectively, (3) risk analysis of the Alert List, and (4) expert ranking of species in the Black List. Amongst species not yet present in the four countries (i.e. Alert List), assessors reliably pointed to the Emerald ash-borer (Agrilus planipennis) and Sosnowski’s hogweed (Heracleum sosnowskyi) as those INNS with the highest risk of invasion and impact. The Japanese knotweed (Fallopia japonica), Himalayan balsam (Impatiens glandulifera), zebra mussel (Dreissena polymorpha) and killer shrimp (Dikerogammarus villosus) were consistently highlighted as some of the most problematic INNS already present in the study area (i.e. Black List). The advantages of our combined approach include that it is inclusive of all-taxa, prioritizes both established and emerging biological threats across trans-national scales, and considers not only the ecological impact, but also potential direct economic consequences as well as the manageability of invasive species.

Using continuous surface water level and temperature data to characterize hydrological connectivity in riparian wetlands

Methods to characterize hydrological connectivity at riparian wetlands are necessary for ecosystem management given its importance over ecosystem structure and functioning. In this paper, we aimed to describe hydrological connectivity at one Ebro River reach (NE Spain) and test a method to perform such characterization. Continuous surface water level and temperature data were recorded at five riparian wetlands during the period October 2006–June 2007. Combining water level and temperature, we classified the examined wetlands in three groups, which mainly differed in the dominant water source during different flood stages. Firstly, a comparison of water level fluctuations in riparian wetlands with those in the river channel during events with different characteristics was used to describe hydrological connectivity. Such comparison was also used to extract quantitative hydrological connectivity descriptors as the wetland response initiation time. Secondly, water temperature series were divided in phases with different average, range and daily oscillation, and these parameters were interpreted for each phase to identify dominant flowpaths. By doing so, a more complete description of hydrological connectivity was achieved. Our method provided useful insights to describe hydrological connectivity using a qualitative approach that can be expanded if required to include quantitative parameters for studies of biotic assemblages or ecosystem processes.

Relationship between invertebrate traits and lateral environmental gradients in a Mediterranean river-floodplain

The aim of the present study was to describe the relationships between macroinvertebrate traits and lateral hydrological and environmental gradients in a Mediterranean river-fl oodplain, from the main river channel to three disconnected fl oodplain wetlands. Bimonthly water and macroinvertebrate samples were collected from an array of riverine wetlands in the Ebro River in northeast Spain. Our analysis of trait structures in wetlands aligned along a lateral hydrological gradient showed that community composition changed from a rich and abundant inver- tebrate community dominated by generalist species adapted to disturbance at the river site to a more trait-diversifi ed community of specialist species adapted to stability and biotic interaction in hydrologically disconnected fl oodplain sites. The diversity of functional groups peaked at intermediate-connected sites, where both generalist and spe- cialist species coexist. The highest richness of functional groups was found in the river site, refl ecting its highest habitat heterogeneity. The main environmental variables shaping the structure of invertebrate traits extracted after Redundancy Analysis were fl ood duration and frequency (surrogates of hydrological disturbance), dissolved solids (surrogate of confi nement) and nitrate concentration (surrogate of agricultural pressure). These environmental vari- ables explained 43 % of the existing variability in invertebrate traits. Because groups with similar traits responded in different ways to the main gradients, we conclude that the functional grouping of invertebrates provides an adequate and simple tool to assess changes in functionality and the effect of lateral gradients across a fl oodplain. Our results highlight the need to integrate the study of rivers and their fl oodplains to better account for their close interaction.