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Abstract

Rivers are impacted by multiple stressors that can interact to create synergistic, additive or antagonistic effects, but experimental studies on fish encompassing more than one stressor are seldom found. Thus, there is the need to study stressors through multifactorial approaches that analyse the impact of fish exposure to multiple stressors and evaluate fish sensitivity to stressor combinations. Some of the most common impacts to Mediterranean rivers are of two natures: i) water abstraction and ii) diffuse pollution. Therefore, the present study aims at studying the responses of potamodromous fish facing combinations of: 1) a primary stressor (two levels of connectivity reduction due to water scarcity), and 2) a secondary stressor (three levels of oxygen depletion due to increase organic load - of anthropogenic nature). Schools of five wild fish from a cyprinid species (Luciobarbus bocagei) were placed in a flume, equipped with see-through sidewalls to allow for behavioural analysis, and subjected to different combinations of the stressors. Results show that at the unconnected level the primary stressor (lack of connectivity) overrode the effect of the secondary stressor (oxygen depletion), but when connectivity existed oxygen depletion caused a reduction of fish movements with decreasing oxygen concentrations. This multifactorial study contributes to improved prediction of fish responses upon actual or projected pressure scenarios.

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... After the trials, fish were returned alive to the river. Further details on fish sampling, holding, and the testing facility are given in Branco et al. [17,18] and Santos et al. [19]. ...
... We reduced oxygen values by adding sodium sulfite (Na 2 SO 3 ). This compound is a recognized oxygen scavenger [23] that has been used to create oxygen-deficient conditions in fish research [18,24], as well as in aquatic research more generally [25,26]. Each experiment lasted for eight minutes (six min acclimation [27] plus two min video-tracking) and was replicated five times, whereby a new subset of fish was used for each trial, giving a total of 75 tested fish. ...
... Hypoxic events affect Mediterranean rivers worldwide [2,29], and fish, in particular, are highly sensitive to reduced oxygen concentrations [9,30]. The ecological impact of such events ranges from beneficial to mortality [31], but common responses include behavioral alterations [5,9,18]. ...
Article
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Numerous anthropogenic stressors impact rivers worldwide. Hypoxia, resulting from organic waste releases and eutrophication, occurs very commonly in Mediterranean rivers. Nonetheless, little is known about the effects of deoxygenation on the behavior of Mediterranean freshwater fish. To fill this knowledge gap, we assessed the impact of three different dissolved oxygen levels (normoxia, 48.4%, 16.5% saturation) on kinematics indicators (swimming velocity, acceleration, distance traveled) and shoaling cohesion of adult Iberian barbel, Luciobarbus bocagei, a widespread cyprinid species inhabiting a broad range of lotic and lentic habitats. We conducted flume experiments and video-tracked individual swimming movements of shoals of five fish. Our results reveal significant differences between the treatments regarding kinematics. Swimming velocity, acceleration, and total distance traveled decreased stepwise from the control to each of the two oxygen depletion treatments, whereby the difference between the control and both depletion levels was significant, respectively, but not between the depletion levels themselves. Shoaling cohesion showed dissimilarities between the treatments regarding the maximum distance between fish, as the high depletion treatment differed from each of the other two, indicating that under severe oxygen depletion some individuals move away from the shoal. Overall, our results show how oxygen depletion changes fish behavior, which may entail ecological responses, highlighting the need to maintain an unfragmented river network to ensure movement dispersal among habitats, thus providing conditions for species escapement from hypoxia.
... As a result, mesocosm systems have been extensively used in stream ecosystem research to improve understanding of multiple stressor effects on freshwater biota (e.g. Branco et al., 2016;Elbrecht et al., 2016;Jones et al., 2015;Matthaei et al., 2010;Piggott et al., 2012;Poff et al., 2003;Schülting et al., 2016). Yet, to our knowledge, macroinvertebrate instantaneous drift patterns still remain poorly understood in the context of interacting effects of reduced flow and increasing oxygen deficit under different seasons. ...
... This baseline DO reduction was followed by an addition of 25 g of Na 2 SO 3 for the subsequent pulses according the frequency established for each treatment (i.e., 1 pulse per hour for dM and 2 pulses per hour for dH treatments). This compound is an acknowledged oxygen scavenger (Lewis, 1970) that has been used in the setting of oxygen-deficit conditions in water research (Branco et al., 2016;Crampton, 1998;Peay et al., 2006). Preliminary tests showed that these amounts of Na 2 SO 3 were sufficient to reduce DO momentarily within a range of 30% to 60% DO (in relation to the control situation -vC + dC). ...
Article
In Mediterranean rivers, water scarcity is a key stressor with direct and indirect effects on other stressors, such as water quality decline and inherent oxygen depletion associated with pollutants inputs. Yet, predicting the responses of macroinvertebrates to these stressors combination is quite challenging due to the reduced available information, especially if biotic and abiotic seasonal variations are taken under consideration. This study focused on the response of macroinvertebrates by drift to single and combined effects ofwater scarcity and dissolved oxygen (DO) depletion over two seasons (winter and spring). A factorial design of two flowvelocity levels - regular and low (vL) - with three levels of oxygen depletion - normoxia, medium depletion (dM) and higher depletion (dH) - was carried out in a 5-artificial channels system, in short-term experiments. Results showed that both stressors individually and together had a significant effect on macroinvertebrate drift ratio for both seasons. Single stressor effects showed that macroinvertebrate drift decreased with flow velocity reduction and increased with DO depletion, in both winter and spring experiments. Despite single stressors opposing effects in drift ratio, combined stressors interaction (vL × dM and vL × dH) induced a positive synergistic drift effect for both seasons, but only in winter the drift ratio was different between the levels of DO depletion. Stressors interaction in winter seemed to intensify drift response when reached lower oxygen saturation. Also, drift patterns were different between seasons for all treatments, which may depend on individual's life stage and seasonal behaviour. Water scarcity seems to exacerbate the oxygen depletion conditions resulting into a greater drifting of invertebrates. The potential effects of oxygen depletion should be evaluated when addressing the impacts of water scarcity on river ecosystems, since flow reductions will likely contribute to a higher oxygen deficit, particularly in Mediterranean rivers.
... Studies at the individual level, namely through behavioural trials measuring the impact of stressors in fish behaviour and movement (e.g. oxygen depletion: Branco et al., 2016; ashes from wildfires: Gonino et al., 2019) are thus critical to understand how populations will respond (Killen et al., 2013;Lennox et al., 2019). To the best of our knowledge, no information exists on the effects of heatwaves on Mediterranean freshwater fish behaviour and activity, particularly of potamodromous cyprinid fish, that perform seasonal migrations within rivers for reproduction, feeding and to seek refuge against harsh environmental conditions. ...
... This study assessed the effect of a simulated heatwave on the behaviour of juvenile Iberian barbel, contributing to reduce the knowledge gap on the effect of these extreme climate events on the behavioural responses of Mediterranean freshwater fishes. Overall, the heatwave treatment was characterized by a daily gradual temperature increase up to 5°C, during six consecutive days and by lower levels of DO relatively to the control, but still considerably higher than the ones used in oxygen depletion studies on the Iberian barbel, which ranged from 1.4 mg L −1 to 4.4 mg L −1 for high and mild oxygen depletion, respectively (Branco et al., 2016;Hayes et al., 2019). ...
Article
Heatwaves, which can be defined as increases of at least 5 °C in air temperature for more than five consecutive days for a specified reference period, are expected to become more frequent under the ongoing climate change, with freshwater organisms being particularly vulnerable to high temperature fluctuations. In Mediterranean-climate areas, depending on the extent of summer droughts and loss of longitudinal connectivity, river segments may become isolated, maintaining fish populations confined to a series of disconnected pools, with no possibility to move to thermal refugia and thus becoming more prone to thermal stress. In this study, we evaluated the effect of a simulated heatwave on the swimming behaviour of juvenile stages of a potamodromous native cyprinid fish, the Iberian barbel Luciobarbus bocagei, under experimental mesocosm conditions. Behavioural traits included fish activity, boldness and shoal cohesion and were continuously measured at a constant flow velocity of 18 cm s⁻¹, which is typical of riffle habitats. Overall, results show that the behaviour of juvenile Iberian barbel is likely to be affected by heatwaves, with fish displaying lower activity and boldness, while no clear difference was observed in shoal cohesion. This study highlights the importance of managing thermal refugia that are crucial for fish to persist in intermittent rivers. Future studies should focus on the interaction of heatwaves with other stressors, such as oxygen depletion, for a broader understanding of the perturbation affecting freshwater fishes under a changing climate.
... The presence of barriers plays an important role in river dynamics and is co-occurrent with several other stressors with which, connectivity fragmentation, as a stressor, may interact synergistically, increasing its deleterious effect on fish (Branco et al., 2016). ...
... The impact (effect size) of this physical stressor is so large that experimental work on potamodromous fish has shown that although individual stressor (oxygen depletion) expressed itself on fish behaviour (Hayes et al., in prep), when in conjunction with connectivity fragmentation, movement response was solely responsive to connectivity (Branco et al., 2016). So, connectivity infringement overrode the effect of oxygen depletion at the movement response level. ...
Thesis
Full-text available
The decline of diadromous fish species has been occurring at least since the beginning of the 20th century. In this thesis, multiple European databases on the historical distribution of diadromous fish were consulted and, acknowledging the lack of data for Portugal, the first database of Portuguese historical data for freshwater fish was created. The existence of multiple databases with distinct geographical coverage and data at different spatial scales lead to the development of an historical data framework able to deal with the limitations of historical data. Its output is a reliable and geographically broad dataset of diadromous species occurrence at the beginning of the 20th century at three spatial scales: basin, sub-basin and segment. Also, a software was developed to facilitate the acquisition of environmental and riverscape variables that can be linked with the data at the three scales. Longitudinal connectivity impairment, climate change and land use alterations are some of the most significant threats to diadromous fish species. The influence of these threats was studied performing a spatial and temporal analysis of the longitudinal connectivity impairment by large dams and, modelling the distribution of diadromous fish at the beginning of the 20th century using climate and land use variables. The longitudinal connectivity impairment of the European freshwater networks became widespread in the second half of the 20th century, and is currently more impactful for populations from basins in southern Europe. The distribution of diadromous fish species is mainly affected by climate, though the effects of land use close to river mouths may be relevant since these are critical passage and entry points for the remaining network. The framework and the software developed were key to achieve the scientific knowledge presented, and more importantly, these can be established as the structural basis for future research on diadromous fish species.
... One of the reasons that may explain our current inability to stop ecosystem degradation (IPBES, 2019) is the failure to fully understand the impacts of multiple stressors on biodiversity and ecosystem functioning (Grizzetti et al., 2017). This constraint often results from methodological limitations to disentangle the complex joint effects of stressors (Schinegger et al., 2016a;Branco et al., 2016;Segurado et al., 2018). Moreover, since stressor effects can interact or add in complex ways (Galic et al., 2018), it is now widely acknowledged that the focus on single stressors is ineffective to anticipate their overall effect on biotic responses. ...
Article
This study aims at understanding how observed inconsistencies in the response of biotic indicators to multiple stressors may result from different stressor gradient lengths being represented at different areas or temporal windows, either as the result of intrinsic natural causes or as the result of sampling bias. We simulated a pool of sites showing five types of interactive responses of indicators to two co-occurring virtual stressors, as well as several sampling constraints, resulting in different portions of each stressor's gradient being covered. The sampled gradient length showed a strong influence on the detection of single stressor effects, both in terms of statistical significance and goodness-of-fit. Increasing constraints on gradient coverage also led to an increasingly deficient identification of stressor interactions. The fail in detecting significant interactions largely dominated over switches between interaction types. The simulations indicated that datasets not fully capturing stressor gradients may hinder the ability to unveil underlying multiple stressor effects. As distinct portions of stressor gradients may be present at different contexts and may change over time, our simulations stress the importance of adaptive management strategies based on robust sampling designs to minimize potential statistical artefacts and uncertainties.
... Regarding the fish abundance, it seems that the changes expected under each scenario are negligible, probably because the treatment has been completed and the future oxygen saturation does not represent a harm for the fish reproduction and life (Branco et al., 2016;Hrycik et al., 2017). However, the management consequences can be different, related to the recreational fishing itself, e.g. because the increase of the activity, needing responses in terms of regulation of fishing, control of fishers and captures, changes in the species permitted for capture, size of the captures and number of individuals (or weight) that can be captured daily (Cardona and Morales-Nin, 2013;Zarauz et al., 2015). ...
Technical Report
Full-text available
In the previous report (D4.1, September 2016) we have developed predictive linkages between indicators of environmental quality and ecosystem services, and different types of pressures, single or multiple, across river basins from all over Europe, in a latitudinal and a west-east gradient, and having very different conditions of climate and land use drivers. Using such predictive linkages resulting both from empirical data treatment and process based modelling, and following a common approach for climatic scenario changes, downscaled to region level, we have studied the future evolution of indicators and services. Furthermore, we have looked into the programs of measures that are being implemented in each country and we attempted to understand how will be the responses of the indicators of quality and services, according to such implementation. The studies performed in these 16 basins have a great potential for common applications and studies, and these are being developed in the moment. Although the hydrological and nutrient process-based models that were used and calibrated at each basin scale mostly contain liaisons between the different water compartments, these studies were mostly focused in surface waters and in the indicators of quality that were developed for the Water Framework Directive, as also the information from monitoring taking pace for the last decade, or in previous times. Many issues remain to be studied, related with interfaces between water compartments and also with the biotic aspects of the pressures, also important for some communities and in some cases. This Deliverable (D4.2) is composed of five reports, dealing with stressor effects at the river basin level. These reports cover special aspects of the linkage between ecosystem compartments, multiple pressures and the responses of particular elements, notably the interface between terrestrial and aquatic environments represented by the riparian transitional ecosystems (D4.2-1), stressor propagation between surface waters and groundwaters (D4.2-2) and estuarine waters (D4.2-3), or deal with particular biological stressor effects when such are added to the more common chemical and physical stressors (D4.2-4 and D4.2-5). Most of these reports use different case studies (D4.2-1, D4.2-2 and D4.2-4) from MARS to pool data and experiences for a common target. The other two focus on the stressor propagation in transitional waters in the example of the estuary of Nervion (D4.2-3) and finally two other are related with biotic pressures, i.e. fisheries management and pathogens (D4.2-4 and D4.2-5). All of these studies will be adapted/are being prepared for publication submission. MARS Deliverable 4.2: Manuscripts on stressor effects at the river basin level The Deliverable 4.2. is therefore composed of five reports, with the non-technical summaries following this introduction: D4.2-1: Riparian-to-catchment management options for stressor reduction and service enhancement D4.2-2: Stressor propagation through surface-groundwater linkages and its effect on aquatic systems D4.2-3: Stressor propagation through inland-transitional linkages and management consequences D4.2-4: Fisheries as a source and target of multiple stressors D4.2-5: Multiple-stressor risks for pathogens Summary of D4.2-1 Riparian management is considered a key management option to improve lotic ecosystem status, functioning and services. Vegetated riparian buffer strips can retain nitrogen from sub-surface runoff, and phosphorous and fine sediments from surface runoff. Thus, they can reduce and mitigate the effects of diffuse pollution by agricultural and other land uses. However, the effectiveness of riparian buffers, to a large extent, depends on the location within the stream continuum, as well as on the land use conditions further upstream of the buffered stream sections. Catchment-scale effects can counteract riparian management effects. In the manuscript, we synthesise the evidence of riparian management options in light of catchment-scale pressures. We reviewed 53 management studies addressing both scales and developed a conceptual model to highlight management options with and without conflicts among management scales. Summary of D4.2-2 The good ecological status of Europe's freshwaters is still lacking. This paper reviews the role of groundwater in these systems and demonstrates that it is an important factor to include in surface water management. Groundwater influences streamflow, water chemistry and water temperature and connects rivers and streams with their catchment and thus functions as a pathway for stressors to reach the surface water. A new 'Groundwater DPS' framework is proposed which shows how groundwater fits in the system of a stressed aquatic ecosystem. The functioning of this framework is demonstrated using examples from four different European lowland catchments: the Thames, Odense, Regge and Dinkel catchments. The importance of groundwater varies between scales, between catchments and within catchments.
... Current knowledge on multiple stressors and related response of fish assemblages is limited in most parts of the world, especially in terms of quantifiable understanding on multiple hydromorphological stress effectssuch as morphological alterations, residual flow and connectivity disruption, hydropeaking and impoundmentspaired with water quality stress. Several studies on local/experimental spatial scale found responses of aquatic organisms (including fish) to multistressor situations, including stressors combined with impoundments (Alonso et al., 2015;Marzin et al., 2012;Van Looy et al., 2014), connectivity disruption and thereby evoked habitat fragmentations by dams and barriers (Alonso et al., 2015;Falke et al., 2013;Van Looy et al., 2014;Branco et al., 2016), water abstractions and residual flow conditions (Lange et al., 2014), morphological alterations (Alonso et al., 2015;Marzin et al., 2012;Milly et al., 2008;Rolls et al., 2013;Van Looy et al., 2014) and hydropeaking (Schülting et al., 2016;Auer et al., 2017;Wright et al., 2016). In contrast, on a very general, pan-European scale, Schinegger et al. (2016) investigated the impact of multiple stressors on fish ecological status in European rivers, including hydromorphological-, connectivity-and water quality stressors, with specific fish metrics responding to certain river types. ...
Article
Full-text available
This work addresses multiple human stressors and their impacts on fish assemblages of the Drava and Mura rivers in southern Austria. The impacts of single and multiple human stressors on riverine fish assemblages in these basins were disentangled, based on an extensive dataset. Stressor configuration, i.e. various metrics of multiple stressors belonging to stressor groups hydrology, morphology, connectivity and water quality were investigated for the first time at river basin scale in Austria. As biological response variables, the Fish Index Austria (FIA) and its related single as well as the WFD biological- and total state were investigated. Stressor-response analysis shows divergent results, but a general trend of decreasing ecological integrity with increasing number of stressors and maximum stressor is observed. Fish metrics based on age structure, fish region index and biological status responded best to single stressors and/or their combinations. The knowledge gained in this work provides a basis for advanced investigations in Alpine river basins and beyond, supports WFD implementation and helps prioritizing further actions towards multi-stressor restoration- and management.
... Potamodromous cyprinid species are particularly affected by the loss of longitudinal connectivity due to their need to perform seasonal reproductive migrations ( Baudoin et al., 2014;Branco et al., 2016;Doadrio, Perea, Garzón-Heydt, & González, 2011;Lucas & Frear, 1997) that are fundamental to complete their life cycle. In addition, the limited swimming and jumping capacity of mature cyprinids when compared to adult salmonids ( Baudoin et al., 2014;Katopodis & Gervais, 2016;Ovidio & Philippart, 2002;Silva, Santos, Franco, Ferreira, & Pinheiro, 2009) further magnify the impacts of barriers. ...
Article
Physical stressors, such as man-made obstacles, are considered one of the main causes that negatively affect freshwater fish. Even small weirs may impact fish populations, including potamodromous cyprinids, by partially or totally blocking upstream migratory movements. Some studies have addressed the effect of key hydraulic parameters on upstream movements past small weirs, but little is known on how these parameters interact to induce swimming or jumping behaviour in negotiating such obstacles. This study aims to evaluate the passage behaviour (swimming vs. jumping) of Iberian barbel (Luciobarbus bocagei), a potamodromous species, over an experimental small broad-crested weir, considering the effect of different plunge pool depths (D), waterfall heights (H), and weir discharges (Q). Results revealed that passage behaviour was highly dependent on combinations of plunge pool depths and waterfall heights. Barbel navigated most configurations by swimming (overall outcomes: 81.5% swimming vs. 18.5% jumping), except the ones with the higher waterfall heights (25 cm) tested. Therefore, higher waterfalls proved to be preponderant in the switching of passage behaviour from swimming to jumping. Regarding the discharge over the 1-m-wide weir (overall outcomes: 85% swimming vs. 15% jumping), contrary to what was expected, there was no evidence that passage behaviour was discharge-related, for the range of discharges tested (25–100 L/s). These results are useful to identify potential migration obstacles and should be taken into consideration in river restoration projects and when designing fishways for potamodromous cyprinids.
... An increase in nutrient concentration may lead, in high insolation areas, to the proliferation of submerged macrophytes and to consequent severe impacts on freshwater fish (Pusey and Arthington, 2003). Branco et al. (2016) also found that, using dissolved oxygen as a proxy in an experimental setup, the input of organic pollution and subsequent degradation seemed to affect fish activity levels. It is known that in some cases the biotic quality status indicators give clear and expectable responses to human induced disturbances, but for other indicators there are weak responses to human stressors, with the strongest responses related to natural environmental variability and spatial processes (Alahuhta and Aroviita, 2016). ...
Article
River basins are extremely complex hierarchical and directional systems that are affected by a multitude of interacting stressors. This complexity hampers effective management and conservation planning to be effectively implemented, especially under climate change. The objective of this work is to provide a wide scale approach to basin management by interpreting the effect of isolated and interacting factors in several biotic elements (fish, macroinvertebrates, phytobenthos and macrophytes). For that, a case study in the Sorraia basin (Central Portugal), a Mediterranean system mainly facing water scarcity and diffuse pollution problems, was chosen. To develop the proposed framework, a combination of process-based modelling to simulate hydrological and nutrient enrichment stressors and empirical modelling to relate these stressors - along with land use and natural background - with biotic indicators, was applied. Biotic indicators based on ecological quality ratios from WFD biomonitoring data were used as response variables. Temperature, river slope, % of agriculture in the upstream catchment and total N were the variables more frequently ranked as the most relevant. Both the two significant interactions found between single hydrological and nutrient enrichment stressors indicated antagonistic effects. This study demonstrates the potentialities of coupling process-based modelling with empirical modelling within a single framework, allowing relationships among different ecosystem states to be hierarchized, interpreted and predicted at multiple spatial and temporal scales. It also demonstrates how isolated and interacting stressors can have a different impact on biotic quality. When performing conservation or management plans, the stressor hierarchy should be considered as a way of prioritizing actions in a cost-effective perspective.
... To test the null hypotheses that fishway configuration (VSF and MSF) had no effect on: (i) the number of upstream and downstream movements; (ii) the number of successes; (iii) the entrance time; (iv) the time to success; and (v) the entry efficiency, a distance-based MANOVA (PerMANOVA) using the Euclidean distance was performed to search for significant differences. PERMANOVA is a powerful non-parametric technique that relies on permutation to make significance tests of small-sized samples possible (Walters & Coen, 2006;Branco et al., 2016). Comparing to a traditional parametric method, such as, ANOVA, this approach offers an advantage, given that the null distribution of the statistical test is determined using permutations, thus, not requiring ecologically unrealistic assumption of normally distributed data (Anderson & Robinson, 2001). ...
Article
Full-text available
Developing and testing new fishway designs is important to improve these facilities. Discharge-efficient passage systems are required in Mediterranean regions and other areas with dry climates. The present study compares the passage performance of the Iberian barbel, Luciobarbus bocagei (Steindachner, 1864), a potamodromous cyprinid, negotiating two different types of vertical slot fishways (VSF): a standard VSF and a multi-slot VSF (MSF). Results show that differences exist between configurations in the number of fish movements through the first slot. The I. barbel performed a significantly higher number of movements in the MSF. However, no differences were found in the entrance time and entry efficiency. The performance was similar between configurations in terms of successes, suggesting that both fishways could be used to restore longitudinal connectivity. Nevertheless, the MSF is a more discharge-efficient configuration, since it requires 31% less water to operate for the same water depth in the pools. Consequently, the velocity and turbulence have lower magnitudes which generally favour the negotiation by smaller individuals. Since it is a more discharge-efficient and cost-efficient configuration, future studies should focus on the passage performance of smaller species to determine if MSF is a useful solution for the whole fish community.
... Fish movement in a stream Stream fish movements can be performed through a short or a long distance. Short distance movements (local) are generally related to changes in resources availability (Albanese et al., 2004), like food or refuge (Gowan, Fausch, 2002;Gowan, 2007), predation risk (Roberts, Angermeier, 2007), or to abiotic conditions like salinity, stream flow Romão et al., 2017), and dissolved oxygen (Branco et al., 2016). Local movements can also be related to ontogeny, being an important life-history trait for several species (Winemiller, Jepsen, 1998). ...
Article
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Given the importance of fish movement to the dynamics and maintenance of stream dwelling fish communities from the Atlantic Forest, we analysed patterns of fish movement in a coastal stream from Southeastern Brazil, using mark-recapture technique. Displacement distance of each species were presented and discussed considering seasonal (rainy and dry) and body size patterns. We marked 10 species along the stream and recaptured 440 (34.6%) of the 1,270 marked fishes. The species with significant number of upstream moving individuals were Astyanax janeiroensis, Characidium interruptum, Astyanax hastatus, Parotocinclus maculicauda and Awaous tajasica. Only Pimelodella lateristriga presented significant differences between resident and moving individuals. Characidium interruptum and A. tajasica demonstrated greater downstream and upstream movement, respectively, moving up to 2,100 m. Even after controlling for species identity we found no significant correlation between fish length and individual displacement distance. Fishes moved longer distances during the rainy season, in accordance to the breeding season. Patterns of fish movement were in agreement to life-history traits of many of the studied species and can be reflecting specific behaviour and morphologies.
... Oxygen depletion was induced by adding sodium sulphite (Na 2 SO 3 ) (Park et al., 2014) into the water of each mesocosm channel, following the same procedure used in a previous parallel study (see Calapez et al., 2017 for further details). As oxygen scavenger (Lewis Jr., 1970), Na 2 SO 3 has been formerly used in the setting of oxygen-deficit conditions in animal and water research (Crampton, 1998;Peay et al., 2006;Branco et al., 2016;Calapez et al., 2017), and was employed in the present study as a proxy for the reduction of DO in rivers due to the degradation of organic loads into the system. ...
Article
River ecosystems are most often subject to multiple co-occurring anthropogenic stressors. Mediterranean streams are particularly affected by water scarcity and organic loads that commonly lead to a simultaneous reduction in flow and increasing depletion of dissolved oxygen. In the present study, the single and combined effects of water scarcity (flow velocity reduction) and dissolved oxygen depletion were used to evaluate alterations of drifting macroinvertebrates on a channel mesocosm system, by employing a multiple trait-based approach. Our main findings confirmed that the impact of the two combined stressors can be implicated in alterations of ecosystem functions as result of the changes in proportions of biological traits. Overall, our results showed that, individually, flow velocity reduction and a severe oxygen depletion promoted a shift in community traits. In more detail, biological traits describing the dispersal of organisms and their respiration showed the strongest responses. The respiration mode responded to low flow with drift increase of gill breathers and decrease of individuals with tegument, whereas dispersal was clearly affected by the combination of stressors. Resistance through eggs was higher with the single effect of flow reduction, while swimmers´ relative abundance increased in individuals that drift after exposure to the combination of stressors. Thus, while flow reduction alone is expected to specifically filter out the gill breathers and the egg producers, the combination of stressors will impact more drastically organism's dispersal and swimmers. Such changes in biological traits can result in variations in ecosystem functioning through, for example, local changes in biomass, secondary production, stream metabolism as well as resulting in biodiversity losses or alterations of its distribution patterns.
... Серія модельних експериментів передбачала визначення інтенсивності дихання риб у зразках води з різними концентраціями речовин відповідно до рибогосподарських нормативів [17]. Обрані для досліджень речовини являють собою типові та широко розповсюджені забруднення водного середовища і характеризуються вираженою біологічною активністю [4]. Під час моделювання концентрацій токсикантів брали до уваги їх лімітуючий показник шкідливості (ЛПШ) і клас небезпеки (табл. ...
Article
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The aim of model experiments were tracking temporal dynamics of breathing intensity tsyhlazoma aquarium fish-zebra (Amatitlania nigrofasciata) at the action of toxicants in different concentrations to determine the approximate levels of assess and the degree of toxicity of the aquatic environment. Fisheries regulations (maximum allowed concentration), caused using various concentrations of substances which are the most common contaminants of the aquatic environment. Fish respiration was assessed by difference in content of dissolved oxygen every 0.5 hrs during the exposure of individuals in the corresponding solution toxicants. The oxygen concentration was measured using instrumental method. As a test parameter coefficient of respiration fish was used. The rate was calculated as the ratio of test reactions version of the experiment and the control. The accuracy of the measu­rements was assessed by the closeness of approximation between the experimental data. The reliability levels of control deviation for each time interval of exposure was tested by Fisher criterion. Statistical rankings of experimental data was carried out within five groups, as recommended by the EU Water Framework Directive regarding the development of the rating scales of ecological state of the aquatic environment. The level of coefficient of fish respiration was ≤50.8 % as recorded in variants of experiment with concentrations of most chemicals at 10 MAC and certain substances at 5 MAC, which was seen as a manifestation of critical toxicity of the aquatic environment for fish. The coefficient of fish respiration within 51.1–101.6% were recorded in some embodiments experiment with concentrations of chemicals at 2 maximum allowed concentration, 3 maximum allowed concentration and 5 maximum allowed concentration, indicating high toxicity. The coefficient of fish respiration 101.7–52.4 % were recorded in variants with concentrations of certain substances at 2, 3 and 1 concentration, which may indicate a moderate or high toxicity. Indicators within 152.5–203.2 % – variations in the concentrations of certain substances at 0.5 concentration, 1 concentration and 2 concentration which was seen as evidence of a weak environment of toxicity to fish. The coefficient of fish respiration ≥203.2 % were recorded 0.5 maximum allowed concentration and 1 concentrations of substances, that was seen as a lack of toxicity. Thus, the methodology of toxicity bioassay of water environment in terms of the intensity of fish respiration, was improved namely: optimal exposure A. nigrofasciata aquarium fish in the experimental samples of water; specified formula of fish respiration intensity during the experiments; proposed indicative scale integrated assessment of the toxicity degree in the aquatic environment. This speeds to obtaining of the integra­ted response of the toxicity of water environment with the ability to reuse test objects.
... In one hand, climatic change shows potential alterations in water temperature and in the magnitude, intensity and frequency of rainfall and consequently in river flow (Solomon et al., 2007). In the other hand, human population growth can cause water scarcity due to the increase in water demand and water pollution as result of industrial, domestic and agricultural waste water (Almodóvar et al., 2012;Branco et al., 2016;Segurado et al., 2016;Vörösmarty et al., 2000). Understanding the isolated and combined impact of all these alterations is necessary for the prediction of responses to changing environments and for the establishment of impact mitigation and compensation measures (Segurado et al., 2016). ...
Article
Brown trout uses river flow and thermal regimens as main stimuli for initiating and maintaining behavioral reactions such as migration and spawning. Therefore, anthropogenic alterations on these factors may have strong impacts on its populations. The aim of this work is to understand these consequences by assessing potamodromous brown trout movements in the past and present, and to model future responses. For this, brown trout movements in a fishway in the Marin River (Bidasoa basin, Northern Iberian Peninsula) have been monitored from 2008 to 2017. Random forest regression has been used to assess the influence of environmental variables on brown trout movements and to model the response under hypothetical climatic and hydrological scenarios. Results show that brown trout uses the fishway during the whole year, with more upstream movements during the spawning season. The model is able to predict accurately the timing and number of migrants. Its use under hypothetical climate change and flow regulation scenarios shows a delay in the migration time. Therefore, modelling using large time series can be a powerful tool to define management and conservation strategies and prepare compensation measures for future scenarios.
... The experiment durations were aligned to the receptor metrics in the study. For instance the trails on fish behavior and invertebrate drift rates only took between 30min and 5 h (Branco et al., 2016;Bruno et al., 2013;Sch€ ulting et al., 2016;Calapez et al., 2017). The experiment on invertebrate community response in natural stream reaches lasted for 334 days (Baumgartner and Robinson, 2015). ...
Chapter
Freshwater ecosystems are among the most imperiled on earth, with rivers being particularly susceptible to anthropogenic stress. Environmental monitoring across Europe reveals that 45% of rivers are affected by more than one human-driven pressure. Detecting and quantifying the impact of multiple stressors exerted from these pressures thus represent important scientific tasks in support of aquatic ecosystem management. This chapter reviews the scientific literature on experimental and field-based observational studies investigating into multistressor effects. Forty experimental and 48 field-based observational studies were covered, dealing with 72 and 151 paired stressor combinations, respectively. Morphological stress paired with either nutrient or hydrological stress was most frequently addressed in both study types. While experiments focused on a broad range of receptor organisms including phytobenthos, benthic invertebrates, fish, microorganisms (e.g., bacteria and fungi) and related processes (e.g., leaf decomposition), field studies mainly investigated the effects on benthic invertebrates and fish. Stressor interactions were more relevant in the experimental studies, with almost 50% of phytobenthos receptor metrics featuring interactions, as compared to the field studies, where stressor interactions were often not specified. Unknown stressor interactions challenge aquatic ecosystem management by posing risks of unwanted “ecological surprises.” Future scientific efforts need to concentrate on classifying the relevance and strength of interactive effects across types of stressors, receptors, and existing ecosystems, considering the specific local conditions of the water bodies to be managed. River basin management will benefit from ecosystem modeling to diagnose the causes of detrimental ecological effects, or to predict the benefits and trade-offs of management strategies in multistressor contexts.
... These effects are thus, in general, of a short duration and limited to smaller streams, as increasing water volume should buffer changes in water quality (Rieman and McIntyre, 1995;Rieman et al., 2012). The present results are however similar with the ones obtained from Branco et al. (2016) who analysed the interactive effect of hypoxia (c. 1.5 mg/L) and reduced connectivity on the movements of this species under experimental conditions and inferred decreased activity in response to an increasing oxygen deficit as would be expected (Domenici et al., 2013). ...
Article
Wildfires are a common phenomenon in Mediterranean regions that is becoming increasingly frequent and severe, causing several environmental concerns, of which ash runoff represents an important source of disturbance for aquatic organisms, in particular for fishes. Studies on the behavioural response of fishes to wildfire ash runoff are scarce and seldom include cyprinid species. The goal of this study was to investigate in a 3-artificial flume channel mesocosm, the behavioural and hepatosomatic condition responses of a native widespread potamodromous fish, the Iberian barbel (Luciobarbus bocagei), previously exposed for 24h to different concentrations of wildfire ashes: 0.0 g/L (the control, no ash), 1.0 g/L (low concentration) and 2.0 g/L (high concentration). Behavioural parameters included i) routine activity, ii) boldness and iii) shoaling cohesion. The hepatosomatic index (HSI) was further determined to assess the health condition of fish. Significant differences on fish behaviour parameters were detected between the control and the high concentration of ash. Accordingly, i) an increasing proportion of fish were found on resting activity (56.2% vs 30.6% in the control), whereas the proportion of fish on searching behaviour (58.4% in the control) decreased (41.5%); ii) the proportion of bolder individuals was found to decrease (42.5% in the control vs. 29.4%) and iii) the same trend was detected for shoaling cohesion (61.3% in the control to 33.8%, of all fish within a body length of each other). Such differences were paralleled by an increase in the HSI from 1.62% (control) to 2.40% (high concentration). The present study shows that even short duration exposure to ash-loaded runoff can alter fish behaviour and hepatosomatic condition and highlights the need to maintain an unfragmented river network, or, when this is not possible, to prioritize the removal or retrofitting of barriers to increase movement dispersal and provide conditions for species recovery from fire-disturbances.
... A far more realistic and effective way to examine the structure of fish community is to perform sampling at medium-to-high water levels with standardized fishing gear and a standardized fishing effort (Flotemersch and Blocksom, 2005). This procedure, which is also common in investigations of fisheries (Achleitner et al., 2012), provides comparable samples and is much more reliable in assessing the effect of stressors acting on an ecosystem (Branco et al., 2016). Furthermore, sampling during high waters, particularly on the Sava River, presents its own challenges and shortcomings and the same catch effort probably does not give the same catch results, which consequently make difficulties to distinguish true changes in the population parameters (Ricker, 1975). ...
Article
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Sampling was undertaken, with the same fishing gear and along the Sava River, from its source to its confluence, in September 2014 and September 2015. In total, 44 fish species were identified, of which 37 were native species and 7 were alien. Fish samples revealed independence in terms of both species composition and their abundance under different hydrological conditions. During flooding and high water levels in 2014, pelagic fish species were sampled in greater proportion than at lower water levels in 2015 when benthic fish species were more abundant. The flood wave in 2014 was accompanied by catch of common carp, Cyprinus carpio, a typical lower rhithron fish species in the upper course, and of tench, Tinca tinca, a typical potamon fish species of backwaters, in the main channel of the lower Sava River. One specimen of bighead goby, Ponticola kessleri, which is common in the potamon fish community, was caught during the 2015 sampling close to the boundary between the upper and middle sections of the Sava. This is the first record of Ponto-Caspian gobies in the inland waters of Slovenia. Its finding far upstream indicates a strong effect of an as yet unidentified stress along the Sava River up to the spot where the bighead goby was sampled. Finally, these results indicate that pelagic fish species are more resistant to the stressful effect of flooding than benthic species, and that the structure of fish communities is influenced/affected by flooding as a short-term stressor. The progressively increasing number of alien fish species downstream in the Sava River point to the effects of long-term human-induced stressors in the area.
... In combination with the fact that macrophytes were slumped into dense pads making it difficult to find stranded fish (Bell et al., 2008), our data may actually underestimate real mortality associated with such dewatering events. Furthermore, in isolated puddles with no connectivity to the main channel, it is possible that a successively progressing oxygen depletion (Branco et al., 2016;Hayes et al., 2019a) would have caused much higher mortality rates than detected in the timely sampling after the dewatering in this study. It needs to be noted that partial dewatering of bank habitats can also be a natural process in free-flowing rivers not affected by hydropower. ...
Article
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Hydropower use of rivers can exert multiple effects on aquatic species and habitats. Due to limitations of conservation projects in the main channels of hydropower-affected rivers, there has been an increasing focus on tributaries, side channels, and fish passes as target areas for conservation and restoration. However, some of these side channels require frequent dewatering for their maintenance, and the ecological effects of such measures remain largely unknown. In this study, we used two dewatering events in a side channel of the River Inn as an opportunity to assess the effects of these common measures on fish. All stranded fish were collected after the two dewatering events in remaining puddles of formerly restored bank habitats, determined to species level, and measured. The fish community was compared by electrofishing before and seven weeks after the dewatering in a subset of the same habitats. The dewatering created one to three remaining puddles in the bank habitats, covering 3% of the assessed bank habitat area. In these remaining puddles, 184 stranded fish from 12 species were found, including species strictly protected under national and international law. In relation to their relative abundance, smaller and less mobile species such as Cottus gobio were mostly affected by stranding in contrast to larger and open-water-oriented species such as Chondrostoma nasus. The dewatering also caused drying out of important nursery zones, resulting in a distinctly lower recruitment success of endangered riverine fish species in the summer following the dewatering. The evidence about the negative ecological effects documented herein should be transferred into policy measures to reduce the impairment of dewatering to a minimum and to contribute to the fulfilment to national and international legal requirements. This can be achieved by reducing the extent and frequency of periodical dewatering to a minimum, by slowing down the dewatering speed, by selecting the least critical time of the year, as well as by compensation measures.
... These threats to fish survival can be independent or can 2 of 8 interact when they co-occur [6]. The correct identification of the threats, or their combination, affecting species is determinant for resource allocation towards species conservation and management [10,11]. This identification has traditionally suffered from the difficulty in establishing causality, especially for threatened or rare species for which experimental work or multi-population comparisons are difficult [12]. ...
Article
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Freshwater ecosystems are disproportionally important for biodiversity conservation, as they support more than 9% of known animal species while representing less than 1% of the Earth’s surface. However, the vast majority of the threats (99%, or 826 out of 837) identified by the International Union for Conservation of Nature Red List of Threatened Species known to affect the 434 known freshwater-dependent fish and lampreys of Europe are not supported by validated published scientific knowledge. This general lack of information about freshwater-dependent fish and lamprey species may have deleterious effects on species conservation, and additional funding is required to fill baseline knowledge gaps.
... PerMANOVA was performed to test the null hypotheses that the number of approaches to the vicinities and the entrances to the L-structure were not significantly affected by those factors. PerMANOVA is a powerful nonparametric technique that relies on permutation to make significance tests of small-sized samples possible [53,54]. This approach offers the advantage that the null distribution of the statistical test is determined using permutations, thus not requiring the assumption of normally distributed data [55]. ...
Article
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The rapid river flow variations due to hydropower production during peak demand periods, known as hydropeaking, causes several ecological impacts. In this study, we assessed the potential of an overhead cover and velocity-refuge structure in an indoor flume as an indirect hydropeaking mitigation measure for the cyprinid species Iberian barbel (Luciobarbus bocagei). We designed a lab-scale LUNKERS-type structure using two different materials which were used separately: Wood (opaque) and acrylic (transparent), tested under hydropeaking and base-flow events. Physiological (glucose and lactate) and behavioral (structure use) responses were quantified. The structure use (inside and in the vicinity) and the individual and schooling behavior was assessed. Although there was no evidence that the hydropeaking event triggered a physiological response, the wood structure use was significantly higher than the acrylic one, where the metrics of use increased in the hydropeaking event. Differences between individual and group behavior were only higher for the entrances in the wood structure. The higher frequency of wood structure use under hydropeaking conditions suggests that the visual stimulus conferred by this shaded refuge enables fish to easily find it. The results suggest that the use of overhead and velocity-refuge structures may act as an effective hydropeaking flow-refuge mitigation measure.
... Increased surface water pollution due to urbanization, excessive water consumptions, population growth, industrial wastewater discharge, and agricultural activities results in low dissolved oxygen (DO) levels and worsens the existence conditions in aquatic systems [1][2][3][4]. Quantification of dissolved oxygen is thus important for evaluating surface water quality because of its representation of the level of pollution and the state of aquatic ecosystem [5][6][7]. ...
Article
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The process of predicting water quality over a catchment area is complex due to the inherently nonlinear interactions between the water quality parameters and their temporal and spatial variability. The empirical, conceptual, and physical distributed models for the simulation of hydrological interactions may not adequately represent the nonlinear dynamics in the process of water quality prediction, especially in watersheds with scarce water quality monitoring networks. To overcome the lack of data in water quality monitoring and prediction, this paper presents an approach based on the feedforward neural network (FNN) model for the simulation and prediction of dissolved oxygen (DO) in the Nyando River basin in Kenya. To understand the influence of the contributing factors to the DO variations, the model considered the inputs from the available water quality parameters (WQPs) including discharge, electrical conductivity (EC), pH, turbidity, temperature, total phosphates (TPs), and total nitrates (TNs) as the basin land-use and land-cover (LULC) percentages. The performance of the FNN model is compared with the multiple linear regression (MLR) model. For both FNN and MLR models, the use of the eight water quality parameters yielded the best DO prediction results with respective Pearson correlation coefficient R values of 0.8546 and 0.6199. In the model optimization, EC, TP, TN, pH, and temperature were most significant contributing water quality parameters with 85.5% in DO prediction. For both models, LULC gave the best results with successful prediction of DO at nearly 98% degree of accuracy, with the combination of LULC and the water quality parameters presenting the same degree of accuracy for both FNN and MLR models.
... Swimming performance has also been shown to be sensitive to other stressors and stressor combinations (e.g. plastic leachates, metals, waterway connectivity; Branco et al., 2016;Little and Seebacher, 2015;Mager and Grosell, 2011) and together lend further evidence that swimming performance is an useful physiological biomarker. Other traits tended to be less sensitive to stressor combinations. ...
Thesis
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The acceleration of anthropogenic activity has caused novel or extreme environmental challenges for species to contend with. Species must now contend with complex combinations of environmental threats which include habitat degradation, pollution, and climate change. Yet, the lack of available data on how species cope when confronted with multiple environmental challenges poses a significant challenge to conservation. Nutrient pollution is regarded as one of the most common and widespread forms of habitat degradation. Anthropogenic activities have caused a rampant increase in nitrate (NO3-) concentrations, peaking at concentrations above 100 mg NO3- L-1. Aquatically respiring organisms (amphibians, amphipods, fish) are particularly vulnerable to elevated nitrate concentrations, causing significant physiological and behavioural alterations. These alterations may be exacerbated by the presence of additional threats, but information on the interactive effects of nitrate and other environmental stressors is scarce. Therefore, the first aim of this thesis was to quantify the impacts of elevated nitrate exposure on key fitness related traits using meta-analytical tools and examine whether organismal survival is affected by nitrate and its interaction with other stressors. Across studies, exposure to elevated nitrate decreased the activity, growth, and survival of aquatic taxa. Further, antagonistic interactions between nitrate and other stressors were most predominant, indicating that future research should focus on interacting stressors that act on the same physiological mechanism (e.g. pH, elevated temperature and hypoxia) as they represent the greatest likelihood for “ecological surprises”. The meta-analysis also revealed that data on fish and crustaceans is limited and these taxa were therefore the focus of subsequent experimental chapters. Environmental pH is one factor that may modify the toxicity of nitrate by exacerbating its uptake and disrupting key physiological performance traits. To test this prediction, blueclaw crayfish (Cherax destructor) were exposed to one of two pH levels (pH 5.0 and 7.0) and three nitrate concentrations (0, 50 and 100 mg NO3- L-1). Aerobic scope (maximal minus standard oxygen uptake rates) was measured at six time points and crayfish performance (chelae strength and righting response) was assessed after 28 days. Aerobic scope was compromised by the interaction between low pH and nitrate and resulted in prolonged elevations of standard oxygen uptake. Declines in aerobic scope corresponded with a lowering of chelae strength and righting capacity. Similarly, combined exposure to nitrate and low pH reduced the aerobic scope and swimming performance of spangled perch (Leiopotherapon unicolor), an effect underpinned by an accumulation of nitrate within the blood and reductions to blood-oxygen carrying capacity. Nitrate-induced reductions to oxygen transport were expected to lower species’ tolerance of, and impede their capacity to compensate for prolonged exposure to, elevated temperatures. To test this prediction, silver perch (Bidyanus bidyanus) were exposed to 28 or 32oC and simultaneously exposed to one of three nitrate concentrations (0, 50 or 100 NO3- L-1). Indicators of performance, aerobic scope and upper thermal tolerance (CTMAX) were assessed after 8-weeks. The aerobic scope of 28oC-acclimated fish declined with increasing temperature, and the effect was more pronounced in nitrate-exposed individuals. Declines in aerobic scope corresponded with poorer swimming performance and a 0.8oC decrease in CTMAX. In contrast, acclimation to 32oC masked the effects of nitrate; swimming performance was thermally insensitive, aerobic scope was maintained, and CTMAX was increased by ~1oC. These results are suggestive of a cross-tolerance interaction and potential mechanisms underlying this interaction were explored by measuring attributes of the heart, gills and blood. Plasticity of the ventricle (increased myocardial thickness) and gill structures (decreased lamellar thickness, interlamellar cell mass) following high temperature acclimation were uncovered, which potentially provide overlapping protection to elevated nitrate concentrations. Lastly, the impact of elevated nitrate on behavioural and physiological responses of silver perch to acute hypoxia were investigated. Fish were exposed to one of three nitrate treatments (0, 50 or 100 mg NO3- L-1) for three weeks, then, behavioural avoidance and aquatic surface respiration (ASR) responses to progressive hypoxia were quantified. Physiological changes evoked under progressive hypoxia were also assessed, including haematological changes, ventilation frequency (VF) and swimming performance. Exposure to elevated nitrate did not alter behavioural avoidance of low oxygen but nitrate-exposed fish did utilise ASR at a higher PO2 threshold during progressive hypoxia. Nitrate exposure had small impacts on key physiological responses; haemoglobin and haematocrit levels were reduced and the VF of nitrate-exposed fish were elevated both at rest and under hypoxic conditions. These physiological disturbances during nitrate exposure had pronounced effects on the swimming performance and hypoxia tolerance of fish and indicate that nitrate pollution is likely to increase the susceptibility of fish to aquatic hypoxia. Overall, presence of nitrate and additional stressors impaired energy homeostasis, such that aerobic scope is reduced and compromised the functioning of aerobically supported traits (e.g. swimming, righting, growth), due to disruptions of the blood-oxygen carrying capacity. Physiological compensation can offset the effects of nitrate, possibly explaining the predominance for antagonistic interactions. This body of work highlights the unpredictability of stressor interactions and underscores the importance of experimental assessments in addressing the eco-physiological constraints of species in our ever-changing world.
... To test the null hypotheses that fishway configuration (VSF and MSF) had no effect on: i) the number of upstream and downstream movements; ii) the number of successes; iii) the entrance time; iv) the time to success; and on v) the entry efficiency, a distance-based MANOVA (PerMANOVA) using the Euclidean distance was performed to search for significant differences. PERMANOVA is a powerful non-parametric technique that relies on permutation to make significance tests of small-sized samples possible Branco et al., 2016). Comparing to a traditional parametric method, such as, ANOVA, this approach offers an advantage, given that the null distribution of the statistical test is determined using permutations, thus, not requiring ecologically unrealistic assumption of normally distributed data (Anderson and Robinson, 2001). ...
... Furthermore, future scenarios of climate change show potential alterations, not only in water temperature but also in the magnitude, intensity and frequency of rainfall and consequently in river discharge (Solomon et al., 2007). This, together with the expected water scarcity as a result of the increasing water demand and pollution for industrial, domestic and agricultural supply and their waste water (Pittock and Lankford, 2010;Seckler et al., 1999), as well as river fragmentation (Nilsson et al., 2005), may negatively affect freshwater populations (Almodóvar et al., 2012;Branco et al., 2016;Sánchez-Hernández and Nunn, 2016;Segurado et al., 2016;Van Vliet et al., 2013;Vörösmarty et al., 2000). ...
Thesis
Full-text available
Many fish species need to move between different habitats in order to complete their life cycles. As a result, migration responds to internal and external factors, with environmental variables, such as river flow and thermal regimes, acting as the main stimuli for the onset and maintenance of migratory behavior in freshwater fish. Moreover, river fragmentation and anthropogenic alterations on these variables (e.g. river regulation) may have strong impacts on fish populations, which could be aggravated by future projections of climate change and increasing water demand. Thus, to assess these impacts and define mitigation measures, it is vital to understand fish movement patterns and the environmental variables affecting them. Native Iberian fish fauna presents the greatest European percentage of endemism, characterized by a low number of families, with most species belonging to the Cyprinidae family. The most representative species from this family are barbels and nases, for example, the Iberian barbel and the Northern straight-mouth nase. However, scarce information exists regarding the ecological requirements of these endemic species during their upstream migration. Another important family in the Iberian Peninsula, in terms of recreational fishing and ecological traits, is the Salmonidae, the brown trout being one of the most representative salmonids worldwide. Although this species has been deeply studied, most available research has been focused on anadromous populations, and studies in the south of its natural distribution are still scarce. The present thesis aims to cover some of these research gaps regarding upstream migration patterns of Iberian barbel, Northern straight-mouth nase and brown trout (both potamodromous and anadromous ecotypes), as well as to determine the environmental conditions which trigger these movements. In addition, this information is used to evaluate the effect of human impacts and assess the effect of mitigation measures on these species. In order to achieve this, the long-term movement data of these three species in four different locations of the Iberian Peninsula (Porma River (León), Tormes River (Salamanca), Marín River (Navarra) and Bidasoa River (Navarra)) were gathered, analyzed and discussed. In all the studied cases, data were collected in fishways, since they are mandatory points of passage during upstream migration. Survival analysis techniques were used to study median migration dates and patterns. Subsequently, random forest regression was used to evaluate the influence of environmental variables on the number of captures, develop models that can predict when upstream movements were more likely to occur, evaluate different scenarios of river discharge and water temperature and assess the possible effects of management and restoration actions. The long-term monitoring is an essential tool, not only for identify population changes, migration patterns and cues, but also for the evaluation of the overall effect of changes in the parameters involved in the migration and assessing the effects of mitigation measures. Therefore, continuous monitoring studies are necessary to define adaptive strategies and reliable management plans to ensure the conservation of Iberian freshwater fish.
... But, less tolerant species may suffer effects at lower salinity concentrations, since they could be exposed to less selective pressures in a natural setting, which would be relevant to understand when researching salinization impacts on other species from other locations (Kültz, 2015;Uliano et al., 2010). Despite Mediterranean fish populations surviving more adverse physical and chemical pressures, human disturbances will continue to increase along with the effects of climate changes (Branco et al., 2016a;Domenici and Seebacher, 2020;Hayes et al., 2019). Moreover, in a natural setting, multiple stressors will likely occur in addition to increasing salinity, and sequential stressful events may have additive, synergistic or antagonistic cumulative effects, intensifying, or not, the effects of salinity in isolation (Branco et al., 2016b;Gunderson et al., 2012;Piggott et al., 2015). ...
Article
Rivers are experiencing increasing anthropogenic pressures and salinity has shown to affect freshwater fish behaviour, potentially disrupting ecological processes. In this study, the aim was to determine the sub-lethal effects of salinization on freshwater fish behaviour, using a widespread native cyprinid species, the Iberian barbel (Luciobarbus bocagei) as the model species. Behavioural trials in a mesocosms setting were performed to assess the effects of three levels of a salinity gradient – control (no salt added to the water, 0.8 mS/cm), low (9 mS/cm), and high concentration (18 mS/cm) – on fish routine activity, shoal cohesion and boldness. Upon increasing the salinity levels in the flume-channels, fish showed a significant reduction on their i) swimming activity (76% of searching behaviour in the control vs. 57% in high salinity), and ii) shoal cohesion (0.95 shoal cohesion ratio in the control vs. 0.76 in high salinity), while iii) an increase of bolder individuals, measured by a higher number of attempts to escape the altered environment (106 total jumps in the control vs. 262 in high salinity), was simultaneously observed. Behavioural changes in fish can reflect shifts in ecological condition. Thus, the behavioural responses of fish caused by salinization stress should be further researched, in addition to the interaction with other environmental stressors, in order to understand the true scope of the consequences of salinization for fish species.
... For migratory fish species, which shift from different habitats (spawning, feeding, refuge) during their life cycle, this habitat loss is particularly worrisome, particularly in the presence of barriers to fish movement, making it essential to assess how habitat may change in the advent of future flow regimes [16]. However, quantifying the impact of climate change in natural populations is challenging, as different effects are expected depending on the climate model trajectories that are assumed [72], the temporal range (mid or late century) and the effect of climate change on the multiple stressors already acting [73]. ...
Article
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Climate change represents a major challenge for the management of native fish communities in Mediterranean rivers, as reductions in discharge may lead to a decrease in passability through small barriers such as weirs, both in temporary and perennial rivers. Through hydraulic modelling, we investigated how discharges from a large hydropower plant in the Tagus River are expected to affect the passability of native freshwater fish species through a rock weir (Pego, Portugal), equipped with a nature-like fish ramp. We considered not only mean daily discharge values retrieved from nearby gauging stations (1991–2005) for our flow datasets, but also predicted discharge values based on climatic projections (RCP) until the end of the century (2071–2100) for the Tagus River. Results showed that a minimum flow of 3 m3 s−1 may be required to ensure the passability of all species through the ramp and that passability was significantly lower in the RCP scenarios than in the historical scenario. This study suggests that climate change may reduce the passability of native fish species in weirs, meaning that the construction of small barriers in rivers should consider the decreases in discharge predicted from global change scenarios for the suitable management of fish populations.
Article
River fragmentation due to artificial barriers directly impacts fish communities by limiting migratory movements. This work aims to understand how small barriers affect the movements of a potamodromous cyprinid species – the Iberian barbel (Luciobarbus bocagei (Steindachner, 1864)) – in a 5.6 km upstream segment of a stream impacted only by the presence of physical barriers. Fish were marked with Visible Implant Elastomer tags (VIE), and barriers were seasonally characterized. A total of 683 fish were tagged, with 104 recaptures, during five sampling seasons (spring 2012 – early summer 2013). Eleven of the recaptured fish moved past a barrier, without any preference in terms of direction of movement. There were no differences in length, either between migrants and residents, or between upstream and downstreammigrants. The results show that although barbel are able to negotiate small barriers, part of the population did not move between fragmented reaches – an indication that under such conditions, fish species populations may adjust their life-history strategy to augment residency as it was hypothesized from the results.
Article
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River fragmentation and alterations in flow and thermal regimes are the main stressors affecting migrating fish, which could be aggravated by climate change and increasing water demand. To assess these impacts and define mitigation measures, it is vital to understand fish movement patterns and the environmental variables affecting them. This study presents a long-term (1995–2019) analysis of upstream migration patterns of anadromous and potamodromous brown trout in the lower River Bidasoa (Spain). For this, captures in a monitoring station were analyzed using Survival Analysis and Random Forest techniques. Results showed that most upstream movements of potamodromous trout occurred in October–December, whereas in June–July for anadromous trout, although with differences regarding sex and size. Both, fish numbers and dates varied over time and were related to the environmental conditions, with different influence on each ecotype. The information provided from comparative studies can be used as a basis to develop adaptive management strategies to ensure freshwater species conservation. Moreover, studies in the southern distribution range can be crucial under climate warming scenarios, where species are expected to shift coldwards.
Article
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Climate models predict an increase in extent, frequency, and duration of marine hypoxia events in the twenty first century. A better understanding of organismal responses to hypoxia in individual species is a crucial step for predicting ecosystem responses. We experimentally subjected a common invertebrate, the bearded fireworm ( Hermodice carunculata ) to two levels of chronic hypoxia and, in a separate experiment, to intermittent hypoxia. We found components of the conserved hypoxia-inducible factor (HIF) pathway and show a modulated response to hypoxia depending on the severity of hypoxic stress: under mild hypoxia, only the HIF-1α subunit is upregulated, while expression of the other subunit, aryl hydrocarbon nuclear translator, only increases significantly at more severe hypoxia levels. The chronic trials revealed down-regulation of genes related to cell adhesion, transport, development and heme-binding, and up-regulation of genes related to glycolysis, oxygen binding, cell differentiation, digestive and reproductive function. The intermittent hypoxia trials revealed an upregulation of heme transporter activity during hypoxia, and our time series analysis characterized nine clusters of genes with similar expression patterns. Our findings suggest that H. carunculata is likely to tolerate, and be resilient to, predicted future hypoxia conditions.
Article
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Fish in stressed conditions will show symptoms of a decreased physiological function. These symptoms include changes in the respiration system (gills, breathing frequency) and blood hemoglobin. Cyprinid fish are active fish that require high oxygen levels. In a minimum oxygen condition, cyprinid fish are easy to get stressed. Despite the extensive literature on cyprinid biology, comparison of declined physiological functions due to oxygen depletion in cyprinid are few and far between. The purpose of this study was to determine the physiological reactions and organ responses of three species of Cyprinidae, common carp (Cyprinus carpio), nilem carp (Osteochilus hasselti), and Torsoro carp (Tor soro) challenged to oxygen depletion. The study was conducted using 18 fishes for each species with an average body weight of 48.11 ± 4.24 g. Oxygen depletion challenge was done by placing the test fish in closed and non-aerated aquaria (40 cm x 20 cm x 20 cm). The dissolved oxygen level in each aquarium was measured every 30 minutes. Fish breathing frequency was calculated by the frequencies of mouth movement every 30 minutes. Histological examination of gills and blood was taken from healthy fish (at the beginning of treatment) and at LC50 (lethal concentration). The results showed that oxygen depletion reduced blood hemoglobin levels down to 5.1 ± 1.4 gram%, 3.3 ± 1.15 gram%, and 1.5 ± 0.71 gram% for goldfish, nilem, and torsoro, respectively. The respiratory rate varied from normal to depleted conditions. When depletion occurred, the respiratory rate increased and decreased again when the fish started to get weak. In normal conditions, the breathing frequency of goldfish was 60 beats/minute, nilem was 108 ± 20.8 beats/minute, and Tor soro was 144 ± 31.7 beats/minute. The highest respiration frequency occurred in tor soro fish in the 150th minute with a value of 216 ± 0.0 beats/minute. The fastest mortality at LC50% occurred in torsoro at 245.00 ± 17.32 minutes.
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RESUMO Os sistemas fluviais são essenciais para a vida e têm sido explorados desde sempre. No entanto, com o aumento da população, aumenta a necessidade de água para vários fins e as pressões exercidas sobre os sistemas aquáticos aumentam de forma continua. As alterações climáticas futuras podem fazer com que o ritmo de aumento destas pressões se torne ainda mais intenso e podem mesmo levar ao incremento do número de stresses a agir em determinado sistema. Estes stresses não agem de forma isolada, agem em combinação com outros stresses. Esta combinação pode ser simplesmente aditiva, ou pode mesmo haver uma interação entre dois ou mais stresses em que um stress afeta o modo com o outro stress se expressa no meio e podem ser de três tipos: antagonísticas, sinergísticas ou opostas. A nível de gestão, a unidade natural é a bacia, uma vez que a estrutura hierárquica e direcional das redes hidrográficas faz com que haja uma dependência do que ocorre na bacia de drenagem primária, mas também do que ocorrer na bacia de drenagem a montante. Sendo assim, o que afeta um segmento tem implicações em todos os segmentos a jusante. De modo a conseguir perceber qual a importância de stresses isolados e em interação, este estudo foca-se na bacia do Sorraia e integra modelos de processos e modelos empíricos de modo a conseguir produzir informação com detalhe suficiente para testar o efeito da interação de stresses em vários indicadores bióticos (Macrófitos, Macroinvertebrados, Fitobentos e Peixes). Escolhemos o SWAT (Soil and Water Assessment Tool) como modelo de processos e modelos baseados em árvores de regressão (Boosted Regression Trees e Random Forests) e em modelos lineares mistos (Linear Mixed Models) como modelos empíricos. Os resultados apontam para uma impossibilidade de aplicar medidas estáticas que tenham um efeito fixo em todo o gradiente do stress, uma vez que o próprio stress pode
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In the present study, two non-linear mathematical modelling approaches, namely, extreme learning machine (ELM) and multilayer perceptron neural network (MLPNN) were developed to predict daily dissolved oxygen (DO) concentrations. Water quality data from four urban rivers in the backwater zone of the Three Gorges Reservoir, China were used. The water quality data selected consisted of daily observed water temperature, pH, permanganate index, ammonia nitrogen, electrical conductivity, chemical oxygen demand, total nitrogen, total phosphorus and DO. The accuracy of the ELM model was compared with the standard MLPNN using several error statistics such as root mean squared error, mean absolute error, the coefficient of correlation and the Willmott index of agreement. Results showed that the ELM and MLPNN models perform well for the Wubu River, acceptably for the Yipin River and moderately for the Huaxi River, while poor model performance was obtained at the Tributary of Huaxi River. Model performance is negatively correlated with pollution level in each river. The MLPNN model slightly outperforms the ELM model in DO prediction. Overall, it can be concluded that MLPNN and ELM models can be applied for DO prediction in low-impacted rivers, while they may not be appropriate for DO modelling for highly polluted rivers. This article has been made Open Access thanks to the kind support of CAWQ/ACQE (https://www.cawq.ca).
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The potential for complex synergistic or antagonistic interactions between multiple stressors presents one of the largest uncertainties when predicting ecological change but, despite common use of the terms in the scientific literature, a consensus on their operational definition is still lacking. The identification of synergism or antagonism is generally straightforward when stressors operate in the same direction, but if individual stressor effects oppose each other, the definition of synergism is paradoxical because what is synergistic to one stressor's effect direction is antagonistic to the others. In their highly cited meta-analysis, Crain et al. (Ecology Letters, 11, 2008: 1304) assumed in situations with opposing individual effects that synergy only occurs when the cumulative effect is more negative than the additive sum of the opposing individual effects. We argue against this and propose a new systematic classification based on an additive effects model that combines the magnitude and response direction of the cumulative effect and the interaction effect. A new class of “mitigating synergism” is identified, where cumulative effects are reversed and enhanced. We applied our directional classification to the dataset compiled by Crain et al. (Ecology Letters, 11, 2008: 1304) to determine the prevalence of synergistic, antagonistic, and additive interactions. Compared to their original analysis, we report differences in the representation of interaction classes by interaction type and we document examples of mitigating synergism, highlighting the importance of incorporating individual stressor effect directions in the determination of synergisms and antagonisms. This is particularly pertinent given a general bias in ecology toward investigating and reporting adverse multiple stressor effects (double negative). We emphasize the need for reconsideration by the ecological community of the interpretation of synergism and antagonism in situations where individual stressor effects oppose each other or where cumulative effects are reversed and enhanced.
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Hypoxia is a common feature in the offshore central basin of Lake Erie. In the late summer of 2012, a strong wind-induced upwelling event transported oxygen depleted water to the nearshore zones of northern Lake Erie. Wind speed, duration and direction relative to the shoreline of individual wind events determined the extent of nearshore zone affected by the hypoxic waters. The upwelling event resulted in adverse water quality along some stretches of the northern shoreline of Lake Erie with persistent anoxia, which was mainly responsible for the mortality of fish.
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Loss of natural river network connectivity is presumed to be one of the more generalized and important human-induced alterations in natural environments and is frequently perceived as one of the main causes of the decline of freshwater fish species.The purpose of the present study was to ascertain the impact of barriers on the distribution of freshwater fish species with distinct life histories. In this study 196 sites in three river basins in Western Iberia were sampled and analyzed for the presence of barriers. Three alternative analytical approaches based on Generalized Linear Models (GLM) were used to test the contribution of connectivity-related variables to species distribution: (1) explore whether connectivity-related variables are included in the best-fitting distribution models; (2) use models calibrated at non-disturbed sites to compute deviations from model predictions made at sites with connectivity-related disturbances; and (3) use a hierarchical partitioning approach, in which the improvement of model fit due to the inclusion of connectivity as a predictor variable is assessed using all possible variable combinations.The results indicate a general lack of influence of barriers on freshwater fish species distributions. The effects of environment and human pressures exceeded the isolated effect of connectivity losses. Further studies based on experimental designs that are more specifically directed at this specific issue are needed in order to fully understand the effects of barriers on species and communities. A more thorough assessment of the effects of connectivity on fish is crucial to the implementation of adequate restoration actions that are in turn needed to achieve the goals of the European Water Framework Directive.
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Fragmentation of freshwater systems is one of the more common human-induced impacts on the environment, and one of the most dramatic because it leads to disconnections among riverine habitats, severely affecting fish populations. To counter this form of ecological abuse, there has been a significant increase of the number of restoration actions. This work approached stream restoration from a holistic point of view, combining habitat modelling with laboratory experimental research. A 2D hydrodynamic model was used to test the increase in weighted usable area (WUA) created by different boulder placement (BP) scenarios in a disturbed site, with a widespread potamodromous cyprinid fish – the Iberian barbel (Luciobarbus bocagei) – as the target species. This was complemented by experimental trials in a full-scale experimental fishway with different bottom substrata arrangements, in order to assess the effects of boulders on barbel movements. Results show that instream BP increases WUA for barbel and facilitates fishway negotiation. The findings reflect the importance of placing instream boulders in fragmented systems in order to enhance suitable habitat area and river connectivity. However, BP must be specifically designed for each case and should always be preceded by a comprehensive study for each site and target fish species.
Article
1.Lower and upper temperature tolerances of 240 goldfish, Carassius auratus, were measured at constant acclimation temperatures of 5, 15, 25 and 35°C via critical thermal methodology.2.Mean critical thermal minima and maxima ranged from 0.3 to12.6°C and 30.8 to 43.6° C, respectively, and were significantly linearly related to acclimation temperature. Acclimation temperature accounted for approximately 90% of the variance in temperature tolerance. Ultimate critical thermal minimum and maximum equaled 0.3 and 43.6°C, respectively.3.Integrating the temperature tolerance polygon yielded an area of temperature tolerance of 1429°C2, which is approximately 17% larger than the polygon measured via the incipient lethal temperature approach. This difference is explained by methodological differences in these two techniques to quantify temperature tolerance.
Article
A previously unrecognized morphological adaptation of fishes to oxygen depletion is described. Natural oxygen depletion was simulated by use of sodium sulfite. It was demonstrated that some fishes are adapted to permit use of an oxygen rich layer of water at the atmosphere-water interface. Representative cypronodontoids (Fundulus notatus, Gambusia affinis, and Poecilia reticulata) exhibited maximum adaptation and the greatest survival ability of the species tested. Notemigonus crysoleucas, Brachydanio rerio, Lepomis macrochirus, and L. cyanellus, representing other suborders, showed less adaptation to these conditions and correspondingly lower survival. Micropterus salmoides seemed unadapted for survival in oxygen depleted waters. Carassius auratus exhibited a physiological adaptation, but used the oxygen rich surface water as a supplement.
Article
Anthropogenic environmental change is exposing animals to changes in a complex array of interacting stressors and is already having important effects on the distribution and abundance of species. However, despite extensive examination of the effects of stressors in isolation, knowledge of the effects of stressors in combination is limited. This lack of information makes predicting the responses of organisms to anthropogenic environmental change challenging. Here, we focus on the effects of temperature and hypoxia as interacting stressors in fishes. A review of the available evidence suggests that temperature and hypoxia act synergistically such that small shifts in one stressor could result in large effects on organismal performance when a fish is exposed to the 2 stressors in combination. Although these stressors pose substantial challenges for fish, there also is substantial intraspecific variation in tolerance to these stressors that could act as the raw material for the evolution of improved tolerance. However, the potential for adaptive change is, in part, dependent on the nature of the correlations among traits associated with tolerance. For example, negative genetic correlations (or trade-offs) between tolerances to temperature and hypoxia could limit the potential for adaptation to the combined stressors, while positive genetic correlations might be of benefit. The limited data currently available suggest that tolerances to hypoxia and to high-temperature may be positively correlated in some species of fish, suggesting the possibility for adaptive evolution in these traits in response to anthropogenic environmental change.
Article
Instream obstacles such as low-head dams and waterfalls are important in fisheries management because they can restrict the movement of fishes. This can have detrimental or beneficial effects on a fish population, depending on whether a particular structure operates as a barrier to migration or as a barrier to invasion. We developed flashboard-type and flume-type adjustable waterfalls in the laboratory to study the effects of waterfall height and plunge pool depth on fish jumping performance. Our ultimate goal was to provide a quantitative method of evaluating pool-and-weir fish passage structures and waterfall barriers that could be applied to field situations. The adjustable waterfalls were successfully tested using adult Rio Grande cutthroat trout Oncorhynchus clarkii virginalis. The flashboard waterfall worked well in experiments where the combined waterfall height and plunge pool depth were less than the depth of the raceway. The flume waterfall worked well for the same conditions, but as designed, its minimum waterfall height was 30 cm. The flume-type waterfall also worked well for tests where the waterfall height exceeded the maximum depth of the raceway. Of the two waterfalls developed, we recommend using the flume-type for future studies because of its greater flexibility, even though it has a higher construction cost and is slightly more difficult to operate.
Article
Laboratory experiments were undertaken to investigate the influences of exposure duration and frequency on the toxicity of short-term pulses of low dissolved oxygen (DO) to fish. For the investigation of exposure duration, rainbow trout (Oncorhynchus mykiss [Walbaum]) and roach (Rutilus rutilus L.) were exposed to a range of DO concentrations in single pulses of 1, 6, or 24 h. For the investigation of exposure frequency, brown trout (Salmo trutta L.) were exposed to 24-h pulses of DO concentrations of 4.0 and 5.5 mg/L at frequencies of once or twice weekly over a period of 75 d. The results suggest that, for a given duration, there is a narrow threshold concentration range above which mortality does not occur and below which mortality rapidly becomes high. This threshold concentration range increases as exposure duration increases. Roach were able to survive lower DO concentrations than trout. Observations on experimental animals following exposure indicated no significant postexposure effects, even at very low DO levels. For the exposure frequencies used here, DO concentration rather than frequency of exposure was the important factor in terms of effect on fish. No significant effects on growth rate were observed but there were significant differences in hemoglobin levels, hematocrit, and organ weights. These results have important implications for the derivation of environmental quality standards aimed at the control of episodic pollution in rivers.
Article
Populations usually persist despite environmental variations. Experimental analysis of responses to stress must include distinction between potential stresses (environmental perturbations that might not cause stress) and actual stress (phenomena that cause a response by the population). This is made difficult by large temporal fluctuations in abundances of many organisms. Monitoring can measure this variability but is insufficient to predict the potential impact of most stresses. Experimental analyses of stresses are also made difficult by differences among populations in their inertia (lack of response to perturbation), resilience (magnitude of stresses from which a population can recover) and stability (rate of recovery following a stress). These attributes of populations cause a range of responses to intermittent, temporary and acute (or ‘pulse’) stresses and to long-term, chronic (‘press’) disturbances. The timing, magnitude and order of stresses can cause different responses by populations. Synergisms between simultaneous or successive stresses can also have unpredictable effects on populations and cause complexity in interpretations of patterns of competition and predation. Experimental manipulations are needed to understand the likely effect of environmental disturbances on populations. The appropriate experiments are those designed to measure the effects of different types, magnitudes and frequencies of simulated stresses. These will be more revealing than the more common experimental analyses used to determine why and how observed changes in abundances of populations are caused by existing stresses.
Article
Key Words flooding, drying, human impact s Abstract Streams in mediterranean-climate regions (areas surrounding the Mediterranean Sea, parts of western North America, parts of west and south Australia, southwestern South Africa and parts of central Chile) are physically, chemically, and biologically shaped by sequential, predictable, seasonal events of flooding and drying over an annual cycle. Correspondingly, aquatic communities undergo a yearly cycle whereby abiotic (environmental) controls that dominate during floods are reduced when the discharge declines, which is also a time when biotic controls (e.g. predation, compe-tition) can become important. As the dry season progresses, habitat conditions become harsher; environmental pressures may again become the more important regulators of stream populations and community structure. In contrast to the synchronous input of autumn litterfall in forested temperate streams, riparian input to mediterranean-type streams is more protracted, with fall and possibly spring peaks occurring in streams in the Northern Hemisphere and a summer peak existing in their Southern Hemisphere counterparts. We present 25 testable hypotheses that relate to the influence of the stream hydrograph on faunal richness, abundance, and diversity; species coexistence; seasonal changes in the relative importance of abiotic and biotic controls on the bi-otic structure; riparian inputs and the relative importance of heterotrophy compared to autotrophy; and the impact of human activities on these seasonally water-stressed streams. Population increases in mediterranean-climate regions (particularly in fer-tile regions) result in an intensification of the competition for water among different users; consequently, water abstraction, flow regulation, increased salinity, and pollu-tion severely limit the ability of the streams to survive as sustainable, self-regulated systems.
Article
Most of the streams in the Mediterranean region are temporary, following predictable seasonal of flooding and drying, with a transition from lotic conditions to shallow lentic conditions. The goal of our study was to assess the nitrogen and phosphorus dynamics in channel-bed processes of temporary streams between floods. Results show that, during winter, temperatures ranged between 9.5 and 11.2 1C and oxygen concentration ranged from 8.0 to 9.5 mg L À1 , whereas, during summer, temperatures varied between 21.2 and 26.8 1C and oxygen between 1.2 and 5.3 mg L À1 , with oxygen depletion in the pools during the night. The nitrate concentrations were far more abundant during winter (February), while ammonium concentration increased after stream fragmentation into pools (especially in July when oxygen depletion conditions favoured ammonification). Results on sediment profiles showed that the most active sediment layers for NH 4 -N are the top 2–3 cm, corresponding to the sediment depositional sites of the stream. Phosphate concentrations had larger variability, yet concentrations decreased from winter to spring and increased again in summer, when the shallow water pools were formed. Sediment profiles at the sediment depositional sites showed that PO 4 -P was more dynamic in the first 6 cm. In Mediterranean temporary streams, nutrient dynamics vary seasonally, as the system transits from lotic conditions to shallow lentic conditions, evidencing the regeneration of nutrients from organic and inorganic matter during the flow cessation period.
Article
Ecosystem resistance to a single stressor relies on tolerant species that can compensate for sensitive competitors and maintain ecosystem processes, such as primary production. We hypothesize that resistance to additional stressors depends increasingly on species tolerances being positively correlated (i.e. positive species co-tolerance). Initial exposure to a stressor combined with positive species co-tolerance should reduce the impacts of other stressors, which we term stress-induced community tolerance. In contrast, negative species co-tolerance is expected to result in additional stressors having pronounced additive or synergistic impacts on biologically impoverished functional groups, which we term stress-induced community sensitivity. Therefore, the sign and strength of the correlation between species sensitivities to multiple stressors must be considered when predicting the impacts of global change on ecosystem functioning as mediated by changes in biodiversity.
Article
This paper explores the relationship between dissolved oxygen concentration and the distribution and electric signal diversity of 64 species of gymnotiforms from the Tefé region of the upper Amazon basin. Seventeen species are able to tolerate protracted periods of anoxia in inundated várzea floodplains or in terra firme swamps. The majority do so by breathing air—either with specialist accessory air-breathing organs or via their gills. An assemblage of 38 species of gymnotiforms which are unable to tolerate hypoxia undertake lateral migrations from well-oxygenated river channels into and out of the várzea floodplain in response to oxygen availability. These have evolved behavioural adaptations to avoid hypoxic water. While there is a mix of tone- and pulse-type electric organ discharges (EODs) in species that live only in permanently well-oxygenated habitats, 16 out of the 17 species that live in anoxic habitats have pulse-type EODs. The tone-type signals may have less flexible and perhaps greater overall energetic demands that impose handicaps in habitats where oxygen is a limiting factor. Many tone-type species also have more active swimming behaviour which could impose further energetic demands.
Article
Several approximate permutation tests have been proposed for tests of partial regression coefficients in a linear model based on sample partial correlations. This paper begins with an explanation and notation for an exact test. It then compares the distributions of the test statistics under the various permutation methods proposed, and shows that the partial correlations under permutation are asymptotically jointly normal with means 0 and variances 1. The method of Freedman & Lane (1983) is found to have asymptotic correlation 1 with the exact test, and the other methods are found to have smaller correlations with this test. Under local alternatives the critical values of all the approximate permutation tests converge to the same constant, so they all have the same asymptotic power. Simulations demonstrate these theoretical results.
Chapter
The European Water Framework Directive offers an unprecedented opportunity for improvement of ecological quality of both freshwater and marine systems. It has implications for every aspect of how catchments are used by human societies and could potentially mean a step change in how waters and catchments are managed. It must be implemented, however, by official bodies, which seem likely to apply ecologically outdated approaches, used in the past simply to manage water quality, to tackle the very different problem of improving ecological quality. Ecological quality can be characterised by parsimony of available nutrients, characteristic physical and biological structure, strong connectivity among systems and mechanisms of resilience to cope with normal, natural change. The implications of these are that high quality systems in a given location do not have unique lists of species and single formulae for how the biodiversity is constituted. They have considerable inherent variability whilst preserving their fundamental functional characteristics. This appears not to have been recognised by official bodies that seek simple taxonomic indices as measures of quality. To some extent this is a function of the way the Directive has been written, but a slavish adherence to this approach may undermine the spirit of the Directive and result in a failure to bring about the fundamental reform that is needed.
Article
Evaluating the success of habitat creation or restoration depends primarily on the selection of appropriate goals, relevant metrics and robust analytic approaches. For intertidal oyster reefs, the goal of restoring ecological function often is as important as the production of harvestable oysters, especially since oysters are the habitat. Assessing differences in resident faunal composition between created and natural reefs is one possible metric for evaluating ecological success. Yearly changes in the resident faunal composition on constructed and natural intertidal oyster reefs at one South Carolina restoration site were analyzed with a variety of statistical approaches to determine the most effective method(s) for documenting possible convergence in the similarity of reef assemblages over time. Two datasets were defined by the level of taxonomic identification, all taxa or a subset of common taxa, and the level of taxa reduction; all taxa, taxa > 1% of total abundance, and taxa significantly contributing to variation. Data were analyzed using “classic” multivariate analysis of variance (MANOVA), null model analysis of co-occurrence (ECOSIM), nonparametric analysis of similarity (ANOSIM), and permutation tests for multivariate analysis of similarity (PERMANOVA). Taxa abundance was used to weight MANOVA and ECOSIM analyses, while the Bray–Curtis dissimilarity index was used to weight ANOSIM and PERMANOVA analyses. Initial constraints on the analytic design and data manipulations resulted in only one test where convergence of the constructed and natural reef assemblages was indicated. Prescribed reductions in the suite of taxa considered did not alter appreciably the results. The analytic approaches varied in suitability and effectiveness at discriminating among changes in compositional similarity, even when initial constraints were relaxed. MANOVA results indicated either no difference or a significant difference in resident faunal composition between reefs, but were compromised by the inability to transform the data sufficiently to test for multivariate homogeneity violations even in analyses with reduced taxa numbers. Interpretation of ECOSIM results suggested fewer taxa in common even on natural reefs and were affected by a lack of design alternatives and the possible inflation of Type I error that weighting by abundance may cause. ANOSIM results identified no significant reef treatment effects and also suffered from design constraints and an inability to generate enough permutations to test for significant differences in datasets with relatively small sample sizes. All test results from PERMANOVA analyses except one indicated unambiguously that resident faunal assemblages on constructed reefs generally were not yet similar to natural reefs even after 7 years. Convergence of constructed and natural reef resident assemblages was suggested by PERMANOVA tests only for the dataset with the fewest taxa. The negligible limitations of PERMANOVA, flexible design options, and ability to generate significance tests for small sample sizes make the approach powerful. The ongoing development of effective statistical approaches for testing the significance of taxonomic compositional changes among habitats makes the determination of whether restoration projects are successful less dependent on the choice of analytic technique. More critical, biological questions including whether convergence of taxa abundance and composition is a valid indicator of similar ecological function remain to be answered.
Article
Hypoxia survival requires a well-coordinated response to either secure more O2 from the depleted environment or to defend against the metabolic consequences of too little O2 at the mitochondria, which limits aerobic ATP production. Inhibition of aerobic ATP production during hypoxia exposure imposes a substrate-limited cap on the duration of survival because O2-independent ATP production (anaerobic) is far less efficient than aerobic ATP production. It has long been held that hypoxia-tolerant animals are able to extend the period of survival under severely hypoxic conditions through a depression of basal metabolic rate, which limits the extent of activation of O2-independent pathways of ATP production. This contention appears to be supported by the available literature; however, more studies measuring metabolic rate during hypoxia exposure are needed before a definitive outcome can be decided. Duration of hypoxia exposure is also an important component to consider when assessing the responses to hypoxia. Long-term hypoxia exposure (> a few hours in some cases) can result in large changes in gene expression, which underlie acclimation/acclimatization and potentially enhance hypoxic survival. Hypoxia-mediated changes in gene expression are likely regulated by the transcription factor, hypoxia inducible factor (HIF), which is well characterized in mammalian systems, but has only recently been examined in fish. Hypoxia inducible factor appears to be regulated in a similar fashion in fish as in mammals, but to date, there does not appear to be a direct link between HIF function and hypoxia tolerance in fish.
Article
The European Water Framework Directive (WFD), which was adopted in 2000, changed water management in all member states of the European Union fundamentally, putting aquatic ecology at the base of management decisions. Here we review the successes and problems encountered with implementation of the WFD over the past 10 years and provide recommendations to further improve the implementation process. We particularly address three fields: (i) the development of assessment methods (including reference conditions, typologies and intercalibration); (ii) the implementation of assessment systems in monitoring programmes; and (iii) the consequences for river basin management plans (such as the design, monitoring and success of restoration measures).