Showing papers in "Hydrobiologia in 2015"
TL;DR: In this article, the authors discuss how changes in water level and salinity related to climate change and water abstraction affect the ecosystem structure, function, biodiversity and ecological state of lakes and reservoirs.
Abstract: According to the Intergovernmental Panel on Climate Change report released in September 2014, unprecedented changes in temperature and precipitation patterns have been recorded globally in recent decades and further change is predicted to occur in the near future, mainly as the result of human activity. In particular, projections show that the Mediterranean climate zone will be markedly affected with significant implications for lake water levels and salinity. This may be exacerbated by increased demands for irrigation water. Based on long-term data from seven lakes and reservoirs covering a geographical gradient of 52° of latitudes and a literature review, we discuss how changes in water level and salinity related to climate change and water abstraction affect the ecosystem structure, function, biodiversity and ecological state of lakes and reservoirs. We discuss mitigation measures to counteract the negative effects on ecological status that are likely to result from changes in climate and water abstraction practices. Finally, we highlight research required to improve knowledge of the impacts of anthropogenically induced changes on lake water level and consequent changes in salinity.
359 citations
TL;DR: Impacts of AIS, factors limiting their dispersal, and the role that humans play in transporting AIS are described, including those that pave the way for invasions by other species (“invasional meltdown”).
Abstract: Humans have effectively transported thousands of species around the globe and, with accelerated trade; the rate of introductions has increased over time. Aquatic ecosystems seem at particular risk from invasive species because of threats to biodiversity and human needs for water resources. Here, we review some known aspects of aquatic invasive species (AIS) and explore several new questions. We describe impacts of AIS, factors limiting their dispersal, and the role that humans play in transporting AIS. We also review the characteristics of species that should be the greatest threat for future invasions, including those that pave the way for invasions by other species (“invasional meltdown”). Susceptible aquatic communities, such as reservoirs, may serve as stepping stones for invasions of new landscapes. Some microbes disperse long distance, infect new hosts and grow in the external aquatic medium, a process that has consequences for human health. We also discuss the interaction between species invasions and other human impacts (climate change, landscape conversion), as well as the possible connection of invasions with regime shifts in lakes. Since many invaders become permanent features of the environment, we discuss how humans live with invasive species, and conclude with questions for future research.
339 citations
TL;DR: Because quagga mussels are found in all regions of a lake, and form larger populations, they may filter larger volumes of water and may have greater system-wide effects, especially in deep lakes, than zebra mussels, which are restricted to shallower portions of lakes.
Abstract: Dreissena polymorpha (zebra mussel) and D. rostriformis bugensis (quagga mussel) continue to spread in Europe and in North America, and have large ecological and economic impacts where they invade. Today many more waterbodies are invaded by zebra mussels, and therefore the extent of their impact is greater than that of quagga mussels. Both species provide additional space and food for invertebrates in the littoral zone, increasing their diversity and density. In contrast, in the profundal zone, quagga mussels may compete for space and food resources with benthic invertebrates, decreasing their diversity and density. The system-wide effect of dreissenids depends on water mixing rates, lake morphology, and turnover rates. Because quagga mussels are found in all regions of a lake, and form larger populations, they may filter larger volumes of water and may have greater system-wide effects, especially in deep lakes, than zebra mussels, which are restricted to shallower portions of lakes. Shortly after initial invasion, as populations increase, both dreissenids will have their largest effects on communities, and most of them will be direct effects. After the initial stage of invasion, impacts are less predictable, and more likely to be caused by indirect effects through changes in the ecosystem.
184 citations
TL;DR: The existence of a sharp decoupling between “dispersal potential” and “actual establishment rates” is stressed, thus urging a definitive overcome of the so-called “Everything is Everywhere” hypothesis in order to gain a proper understanding of the biogeography and ecology of inland water organisms.
Abstract: Lakes and ponds are scattered on Earth’s surface as islands in the ocean. The organisms inhabiting these ecosystems have thus developed strategies to pass the barrier represented by the surrounding land, to disperse and to colonize new environments. The evidences of a high potential for passive long-range dispersal of organisms producing resting stages inspired the idea that there were no real barriers to their actual dispersal, and that their distribution was only limited by the ecological characteristics of the available habitats. The development of genetic techniques allowed to criticize this view and revealed the existence of a more complex and diverse biological scenario governed by an assortment of historical and ecological factors. In this paper, we review the literature related to the passive dispersal of organisms producing resting stages among inland lentic ecosystems, with special emphasis to temporary ponds, which represent “isolated” ecosystems both in space and in time, and are characterized by high levels of biological diversity. The existence of a sharp decoupling between “dispersal potential” and “actual establishment rates” is stressed, thus urging a definitive overcome of the so-called “Everything is Everywhere” hypothesis in order to gain a proper understanding of the biogeography and ecology of inland water organisms.
184 citations
TL;DR: The macrobenthic fouling community that developed on the concrete foundations of the first wind turbines built in Belgian marine waters is investigated, with a clear vertical zonation, and NIS were found to use the foundations to expand their range and strengthen their strategic position in the area.
Abstract: In recent years, offshore wind energy in the shelf seas of the southern North Sea is experiencing a strong growth. Foundations are introduced in mainly sandy sediments, and the resulting artificial reef effect is considered one of the main impacts on the marine environment. We investigated the macrobenthic fouling community that developed on the concrete foundations of the first wind turbines built in Belgian marine waters. We observed a clear vertical zonation, with a distinction between a Telmatogeton
japonicus dominated splash zone, a high intertidal zone characterised by Semibalanus balanoides, followed by a mussel belt in the low intertidal–shallow subtidal. In the deep subtidal, the species turnover was initially very high, but the community was soon dominated by few species (Jassa herdmani, Actiniaria spp. and Tubularia spp.), and only seasonal dynamics within this species assemblage were observed after 1–1½ years. Ten non-indigenous species (NIS) were found. In the intertidal, eight out of the seventeen typical intertidal species observed were NIS, while only two out of a species pool of 80 species were NIS in the deep subtidal. NIS were found to use the foundations to expand their range and strengthen their strategic position in the area.
113 citations
TL;DR: In this article, the authors tested the hypothesis that floods decrease environmental and biological variability using data from a near-pristine floodplain in Central Amazon (Brazil) and found that environmental variability and zooplankton beta diversity were significantly decreased by the flood, and they postulate that floods act as "rubber erasers", reducing the environmental and ecological idiosyncrasies created during low water periods.
Abstract: Floods are major determinants of ecological patterns and processes in river-floodplain systems. Although some general predictions of the effects of water level changes on ecological attributes have been identified, specific tests using the flood pulse concept are scarce, mainly in tropical areas, where large river-floodplain systems abound. We tested the hypothesis that floods decrease environmental and biological variability using data from a near-pristine floodplain in Central Amazon (Brazil). We recorded nine limnological variables and the zooplankton community structure at eleven sites during one low and one high water period. During the low water period, when the levels of hydrological connectivity were low, asynchronous processes (e.g., sediment disturbance by biota, decomposition, and predation) likely determined the large environmental and biological heterogeneity in the floodplain. On the other hand, environmental variability and zooplankton beta diversity were significantly decreased by the flood. We postulate that floods act as “rubber erasers”, reducing the environmental and ecological idiosyncrasies created during low water periods. Also, we suggest that dilution effects and enhanced connectivity during the high water period, along with species sorting during the low water period, may determine zooplankton beta diversity patterns in river-floodplain systems.
113 citations
TL;DR: This article found that stormwater management can occur alongside biodiversity enhancement in urban areas, but correlations between urban land use, water chemistry, and the structure of biological communities suggests that run-off from urban areas is likely a major factor in structuring biological communities in built-up regions.
Abstract: Urban freshwaters provide a range of ecosystem services, including stormwater management, water treatment, biodiversity, and aesthetics. Management of freshwaters should aim to maximise as many of these services as possible, but managers are often focused on individual services. To test for the biodiversity value of stormwater management ponds (SMPs) in Ottawa, Canada, 20 SMPs were surveyed for macroinvertebrates using standardised sampling techniques. These were compared against 10 wetlands that were not managed for stormwater control (a combination of ornamental lakes, natural lakes, and nature reserves) in and around the same urban area (a total of 30 ponds). Natural wetlands and SMPs were very different in their water chemistry, which was correlated with the proportion of urban land use within 1 km of the site, with higher conductivity in SMPs with increasing urban land cover (P = 0.046). Despite this, natural wetlands and the richest SMPs contained similar levels of biodiversity and similar macroinvertebrate community structure. This study highlights that stormwater management can occur alongside biodiversity enhancement in urban areas, but correlations between urban land use, water chemistry, and the structure of biological communities suggests that run-off from urban areas is likely a major factor in structuring biological communities in built-up regions.
106 citations
TL;DR: Limnoperna fortunei was introduced in South America around 1990 and has been shown to enhance light penetration and stimulate growth of periphyton and macrophytes as discussed by the authors.
Abstract: We summarize current knowledge on the effects of the invasive Asian bivalve Limnoperna fortunei (introduced in South America around 1990) on local biota. Limnoperna modifies nutrient concentrations and decreases concentrations of particulate organic matter in the water column (including phytoplankton and zooplankton), thus enhancing light penetration and stimulating growth of periphyton and macrophytes. Selective grazing and modification of the N:P ratio are responsible for strong enhancements of toxic cyanobacterial blooms. Limnoperna beds significantly enhance the numbers, biomass, and diversity of practically all accompanying invertebrates. The mussel’s planktonic larvae represent an important food item for the larvae of 18 fish species, while juveniles and adults are consumed by at least 50 fish species. Limnoperna is the first and only abundant benthic filter-feeding animal in South American continental waters. The fact that it intercepts and retains in the freshwater lotic domain particulate organic matter that would otherwise be swept into the sea must represent an important energetic subsidy, but the ecosystem-wide consequences of this trophic shift have not yet been addressed. Comparison with the impacts of the zebra mussel in Europe and North America suggests important differences.
106 citations
TL;DR: Temporal comparisons of the fishes support the hypothesis that biotic homogenization occurred at the interbasin scale, whereas the biotic differentiation was observed at the intrabasin scale, and decrease in species richness serves as the variable that best explained changes in biological diversity.
Abstract: Non-native species introduced into reservoirs cause major changes in biodiversity, resulting in spatial and temporal biotic homogenization and/or differentiation. We used a sampling standardized temporally and spatially in reservoirs of basins located in the Neotropics, the Coastal, Iguacu, and Upper Parana basins. Our analyses were conducted at the interbasin and intrabasin scales, aimed at: (i) identifying the non-native species and their major vectors of introductions, (ii) assessing temporal and spatial changes in the fish assemblages, and (iii) evaluating temporal changes in the beta diversity of the basins/reservoirs. The spatial occupation of non-native species was variable, with Tilapia
rendalli, Cyprinus carpio and Oreochromis niloticus the most frequently introduced species. This highlights aquaculture as the main vector of invasives on a large spatial scale. The percentage of non-native species at the interbasin and intrabasin scales increased over time. Temporal comparisons of the fishes support the hypothesis that biotic homogenization occurred at the interbasin scale, whereas the biotic differentiation was observed at the intrabasin scale. Beta diversity decreased over time at the interbasin and intrabasin scales, with decrease in species richness serving as the variable that best explained changes in biological diversity. There was no relation between beta diversity and time for the Iguacu.
91 citations
TL;DR: In this article, the authors examined mechanisms that contribute to macrophyte invasion through a literature review, including competition, enemy release, evolution of increased competitive ability, mutualisms, invasional meltdown, novel weapons, allelopathy, phenotypic plasticity, naturalization of related species, empty niche, fluctuating resources, opportunity windows and propagule pressure.
Abstract: Aquatic plants (macrophytes) are important components of freshwater ecosystems and serve numerous purposes that structure aquatic communities. Although macrophytes represent an essential component of stable aquatic communities, invasive macrophytes negatively alter ecosystem properties. Non-native, invasive species have been identified as a major cause of biodiversity loss and the increasing prevalence of invasive species has prompted studies to help understand their impacts and to conserve biodiversity. Studying mechanisms of invasion also give insight into how communities are structured and assembled. This paper examined mechanisms that contribute to macrophyte invasion through a literature review. Mechanisms identified with this review included competition, enemy release, evolution of increased competitive ability, mutualisms, invasional meltdown, novel weapons, allelopathy, phenotypic plasticity, naturalization of related species, empty niche, fluctuating resources, opportunity windows, and propagule pressure; and were then placed within the context of the invasion process. Results of this review indicated that many invasion mechanisms have been tested with fully aquatic macrophytes with varied levels of support (i.e., some mechanisms are not supported by evidence in the context of macrophyte invasions). Future research should continue the search for evidence of invasion mechanisms that allow introduced species to establish. It is likely that general principles governing these invasions do not exist, at least among comparisons across ecosystem types. However, ecologists should continue to search for general patterns within definable ecosystem units to increase understanding about factors contributing to invasibility.
88 citations
TL;DR: The matrix of the number of fish species per vectors explained the greatest proportion of the composition of non-native assemblages, whereas the geographic distance and age of the reservoir explained few of these variations.
Abstract: Several human activities may result in or facilitate species introductions. In aquatic environments, species introductions are often associated with the construction of dams. In this study, we use reservoirs of the Neotropical region as a model to determine the main causes of fish species introductions. We compiled information on non-native fish species present in reservoir ichthyofauna surveys in the past 14 years and classified these species based on their probable reason for introduction (vector). Fish farming activities introduced approximately 7.6-fold more species in reservoirs than the other vectors identified. The matrix of the number of fish species per vectors explained the greatest proportion of the composition of non-native assemblages, whereas the geographic distance and age of the reservoir explained few of these variations. The non-native ichthyofauna composition varied among Neotropical basins and can be explained by the different sets of species introduced by the companies managing the reservoirs. Although power companies have banned stocking with non-natives, fish farming in the Neotropical region continues to use non-native species, and these species are occupying water bodies, especially reservoirs.
TL;DR: This special issue of Hydrobiologia includes 31 papers on aquatic invasive species and the factors that influence their dispersal and success, along with their impacts.
Abstract: Invasion rates are increasing worldwide and most are due to the actions of humans. Deliberate introductions, escapes, and hitchhiking with global commerce transport species to other continents. While most species fail to thrive or have minor impacts on their new ecosystems, the large number of introductions has led to numerous problems. Aquatic invasive species are particularly pervasive and may cause food web disruption, biodiversity loss, and economic harm. Biological invasions appear in an increasing number of publications in the aquatic and general ecology literature. This special issue of Hydrobiologia includes 31 papers on aquatic invasive species and the factors that influence their dispersal and success, along with their impacts. Ecosystems include freshwater ponds, lakes and reservoirs, small streams and large rivers, and coastal marine systems. Study regions occur in temperate, as well as less-studied tropical and sub-tropical regions of four different continents. We discuss the dynamics of invasive species research in the current literature and provide a brief overview of the contributions to this issue.
TL;DR: A brief and selective review of invasive alien aquatic plant species can be found in this paper, where the authors focus on a set of 21 alien aquatic plants (notably the 21 listed by the European and Mediterranean Plant Protection Organisation), including five A2 species, 11 invasive, 2 in the Observation List, 1 in the Alert List, 2 noteworthy).
Abstract: The present brief and selective review focuses on a set of invasive alien aquatic plant species (notably the 21 listed by the European and Mediterranean Plant Protection Organisation, i.e., five A2 species, 11 invasive, 2 in the Observation List, 1 in the Alert List, 2 noteworthy), on definitions in use, on introduction pathways, and ecological effects, although the social and economic effects of freshwater invaders can be diverse and substantial. Legislation, literature, and scientific research dealing with plant invasions in inland waters often merge different types of invasive plant species and invaded habitats, as there are some overlappings between the concepts of macrophyte, aquatic plants, inland waters, wetlands, and riparian habitats. Freshwater ecosystems may well be the most endangered ecosystems in the world. Countless aquatic plants have been introduced in Europe and in the Mediterranean region, either deliberately because they were thought to be ornamental or otherwise desirable, or accidentally as releases from aquaria, dumping from water gardens, or contaminants. The escape of alien plants from managed environments is also frequent. Aquatic invaders have strong negative impacts on native biodiversity and many different impacts are reported in the literature for Europe and worldwide. Plant invasions in inland waters may be considered as one of a syndrome of factors that characterize degraded aquatic ecosystems. There are a number of risk analysis, impact assessment, ranking systems, decision trees, and prioritization methods available throughout Europe and the EPPO region, but the lack of a common framework for assessing the risks posed by invasive alien aquatic species is seen as a key gap. Successful management should include prevention, habitat restoration, dedicated risk assessment, prioritization, awareness raising, dedicated legislation, collaboration between different stakeholders, development of codes of conduct with the horticultural sector, and prohibiting the sale, purchase, and intentional release of some species in the wild. Actions to protect the European and Mediterranean inland waters from plants invasions are urgently needed and could provide overarching benefits.
TL;DR: In this paper, the authors provided a synthesis of the climate, geology, and hydrological network of the Central Plains of Argentina and focused on Pampean shallow lakes from a global perspective, comparing the limnological variables: total phosphorus concentration, total nitrogen concentration (TN), chlorophyll a (Chl a) concentrations, and Secchi disk reading (SD) from a compiled database.
Abstract: The Central Plains of Argentina is a heterogeneous environment, but the lakes there share some fundamental features: they are all shallow and polymictic as being well exposed to wind. First, we provide a synthesis of the climate, geology, and hydrological network. We also discussed shallow lakes origin and their limnological and biological salient features. Second, we focus on Pampean shallow lakes from a global perspective, comparing the limnological variables: total phosphorus concentration (TP), total nitrogen concentration (TN), chlorophyll a (Chl a) concentrations, and Secchi disk reading (SD) from a compiled database. No significant differences in the Chl a vs. TP relationship were found between Pampean and other shallow lakes. Otherwise, the chlorophyll yield per unit of phosphorus of Pampean lakes is similar to the world shallow lakes average. Moreover, the relationship SD vs. Chl a differed significantly between Pampean and the remaining world lakes, about 50–60%. When confronted against other lakes worldwide, Pampean shallow lakes depart from most of them as having higher TP, TN, and Chl a concentrations and much lower SD transparency, and therefore they stand as extremes of the trophic-state continuum. Despite their highly turbid state, these lakes provide valuable ecosystem services that are highly appreciated and mobilize important economic resources.
TL;DR: Emmphasis on contrasts between Neotropical and Afrotropical lineages improves characterization of patterns at a broader level of organization and indicates that the genetic basis, functional capacity, and ecological opportunity for many traits may be conserved across lineages.
Abstract: Cichlid fishes are hypothesized to encompass several independent adaptive radiations that display increased diversification rates and impressive ecological heterogeneity. Here, I review major ecological patterns associated with the evolutionary history of cichlids, with particular focus on comparison of Afrotropical and Neotropical lineages. Specifically, I present major patterns of ecological diversification, potential mechanisms that may promote ecological diversification, and possible consequences of ecological diversification. Evolutionary convergence and specialization of ecological (e.g., diet), behavioral (e.g., benthic sifting), and morphological traits (e.g., oral dentition) characterize adaptive patterns that transcend continents. Craniofacial mechanics, the pharyngeal jaw apparatus, phenotypic plasticity, and hybridization may have facilitated diversification of cichlid fishes by generating functional, morphological, and/or genetic diversity. The benthic–pelagic axis has been an important source of divergence during adaptive radiation. Additionally, there are several discrepancies between Afrotropical and Neotropical lineages, such as the relative frequency of herbivorous species, the importance of hybridization in generating diversity, the relative frequency of dentition types, and relationships between dental organization and ecological function. Emphasis on contrasts between Neotropical and Afrotropical lineages improves characterization of patterns at a broader level of organization and indicates that the genetic basis, functional capacity, and ecological opportunity for many traits may be conserved across lineages.
TL;DR: Combined observations on impact strength, information type and confidence level suggest that the two benthic invertebrates, the polychaete Marenzelleria spp.
Abstract: Invasion of non-indigenous species (NIS) is acknowledged as one of the most important external drivers affecting structure and functions of marine ecosystems globally. This paper offers literature-based analysis on the effects of the widespread (occurring in at least 50% of countries) and currently established NIS on ecosystem features in the Baltic Sea. It appears that out of the 18 NIS taxa studied, there are no published records on 28% of NIS for any of the seven impact categories investigated. When ecological impacts are known, laboratory experimental evidence dominates over field studies. Combined observations on impact strength, information type and confidence level suggest that the two benthic invertebrates, the polychaete Marenzelleria spp. and the zebra mussel Dreissena polymorpha (Pallas 1771) exert the highest ecosystem impact. Despite continuously accumulating information on the NIS effects, however, the confidence of findings is still low. Thus, we still understand very little on both the direction and magnitude of the effects of even the most widespread NIS on the structure and dynamics of the Baltic Sea ecosystems. In order to increase reliability of such assessments, future research should be targeted towards spatially-explicit field surveys and experimenting of multitrophic systems, together with modelling of ecosystem impact.
TL;DR: In this paper, the abundance of 18 O isotope in stem water was used to assess the extent of fresh water utilization by Avicennia marina (Forssk.) Vierh across hydrological settings; and whether growth, measured as increments in stem circumference, is sensitive to variation in rainfall availability.
Abstract: Mangroves are distributed along tropical and subtropical riverine and coastal shores. Although mangroves are highly adapted to saline environments, maintaining water uptake under saline conditions is energetically expensive. Therefore, salinity is a lim- iting factor for mangrove growth and productivity, and access to fresh water sources, such as rainwater and groundwater, which reduce water salinity, increase mangrove ecosystem productivity. Here, we investi- gated the extent of fresh water utilization by man- groves to better predict current and future mangrove productivity. We used the abundance of 18 O isotope in stem water to assess: (1) the extent of fresh water utilization by Avicennia marina (Forssk.) Vierh across hydrological settings; and (2) whether growth, mea- sured as increments in stem circumference, is sensitive to variation in rainfall availability. The d 18 O isotopic composition of stem water indicated mangroves use both fresh and saline water sources for metabolic processes. However, our results suggest that the proportion of fresh water used by mangroves increases with the availability of fresh water. Growth of the main stems of trees was correlated with rainfall (r 2 = 0.34 and r 2 = 0.37, P = 0.001). Our results
TL;DR: In this article, the authors proposed that P would not be the limiting nutrient for phytoplankton growth in Grahamstown Dam, a shallow, mesotrophic reservoir, across different seasons and on different experimental time scales.
Abstract: Phosphorus (P) limitation has been regarded as the rule in freshwater systems and the basis for phytoplankton growth management. We hypothesised that P would be the limiting nutrient for phytoplankton growth in Grahamstown Dam, a shallow, mesotrophic reservoir, across different seasons and on different experimental time scales. Seven fully factorial microcosm assays with additions of nitrogen (N) and P were conducted in situ during different seasons. The influence of longer experimental duration was examined in two 18-day mesocosm assays. Additions of N and P in combination evoked significantly higher phytoplankton biomass and biovolumes of individual algal genera compared with controls and other treatments in both types of experiment. There were some significant responses to P additions in the microcosm assays in winter. Some genera first responded to combined P and N addition and then to P only addition during the mesocoms assays. Our results show that P was not the limiting nutrient across all seasons but that phytoplankton was mostly co-limited by N and P. A longer experimental time scale did not change this outcome at the biomass level. This implies that input of N as well as of P should be considered in the management of phytoplankton growth.
TL;DR: The extensive published and unpublished literature on the biology and ecology of Antarctic toothfish in the Ross Sea region including distribution, stock structure, reproduction, age and growth, and trophic ecology in a single document for the first time is summarised.
Abstract: The Antarctic toothfish (Dissostichus mawsoni, Norman) is a large notothenioid fish that supports valuable fisheries around the Antarctic continent. The Ross Sea fishery, which started in 1997, is managed by the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR). Whilst a large amount of research into the biology of this species has been carried out over the past decade, much of this work has been presented in CCAMLR working group papers and has not been published in the primary literature. In this paper, we bring together and summarise the extensive published and unpublished literature on the biology and ecology of Antarctic toothfish in the Ross Sea region including distribution, stock structure, reproduction, age and growth, and trophic ecology in a single document for the first time. We also review and further develop testable hypotheses surrounding its life cycle and identify gaps in our knowledge including spawning behaviour and early life history which need to be addressed.
TL;DR: The development of a multimetric index using benthic macroinvertebrates (BMI) to assess the ecological health of highland rivers in Ethiopia showed that the index is stable along different hydrological conditions and sensitive to the current range of anthropogenic disturbances in Ethiopian high land rivers.
Abstract: This study presents the development of a multimetric index using benthic macroinvertebrates (BMI) to assess the ecological health of highland rivers in Ethiopia. BMI were collected from 22 reference and 82 impaired sites determined based on hydro-morphological, land use, and physical and chemical criteria. Of 75 potential metrics tested to integrate the multimetric index, only nine core metrics were selected based on their abilities to distinguish reference and impaired sites, strength of correlation with pertinent environmental parameters, and their independence from other metrics. The metrics retained in the multimetric index were total number of taxa, EPT-BH > 1sp (Ephemeroptera, Plecoptera, and Trichoptera taxa where Baetidae and Hydropsychidae taxa are considered if they consist more than one taxon), % Oligochaeta and Red Chironomidae, % COPTE (Coleoptera, Odonata, Plecoptera, Trichoptera, and Ephemeroptera), % EPT-BCH (EPT without Baetidae, Caenidae, and Hydropsychidae), ASPT-SASS (Average South African Scoring System Per Taxa), FBI (Family Biotic Index), % shredders, and % collector gathering. The final index derived from these metrics was divided into five river quality class (high, good, moderate, poor, and bad). A validation procedure showed that the index is stable along different hydrological conditions and sensitive to the current range of anthropogenic disturbances in Ethiopian highland rivers.
TL;DR: The Yela River and Sapwalap River, Federated States of Micronesia, contain a natural soil resource gradient defined by total phosphorus (P) density ranging from 0.05 to 0.42 in different hydrogeomorphic settings as mentioned in this paper.
Abstract: Belowground biomass is thought to account for much of the total biomass in mangrove forests and may be related to soil fertility. The Yela River and the Sapwalap River, Federated States of Micronesia, contain a natural soil resource gradient defined by total phosphorus (P) density ranging from 0.05 to 0.42 mg cm−3 in different hydrogeomorphic settings. We used this fertility gradient to test the hypothesis that edaphic conditions constrain mangrove productivity through differential allocation of biomass to belowground roots. We removed sequential cores and implanted root ingrowth bags to measure in situ biomass and productivity, respectively. Belowground root biomass values ranged among sites from 0.448 ± 0.096 to 2.641 ± 0.534 kg m−2. Root productivity (roots ≤20 mm) did not vary significantly along the gradient (P = 0.3355) or with P fertilization after 6 months (P = 0.2968). Fine root productivity (roots ≤2 mm), however, did vary significantly among sites (P = 0.0363) and ranged from 45.88 ± 21.37 to 118.66 ± 38.05 g m−2 year−1. The distribution of total standing root biomass and fine root productivity followed patterns of N:P ratios as hypothesized, with larger root mass generally associated with lower relative P concentrations. Many of the processes of nutrient acquisition reported from nutrient-limited mangrove forests may also occur in forests of greater biomass and productivity when growing along soil nutrient gradients.
TL;DR: In this article, the authors examined the effects of fine sediment (FS) on the movement of Gammarus pulex Linnaeus (Crustacea: Amphipoda) into subsurface sediments in response to surface water loss.
Abstract: Surface and subsurface sediments in river ecosystems are recognized as refuges that may promote invertebrate survival during disturbances such as floods and streambed drying. Refuge use is spatiotemporally variable, with environmental factors including substrate composition, in particular the proportion of fine sediment (FS), affecting the ability of organisms to move through interstitial spaces. We conducted a laboratory experiment to examine the effects of FS on the movement of Gammarus pulex Linnaeus (Crustacea: Amphipoda) into subsurface sediments in response to surface water loss. We hypothesized that increasing volumes of FS would impede and ultimately prevent individuals from migrating into the sediments. To test this hypothesis, the proportion of FS (1–2 mm diameter) present within an open gravel matrix (4–16 mm diameter) was varied from 10 to 20% by volume in 2.5% increments. Under control conditions (0% FS), 93% of individuals moved into subsurface sediments as the water level was reduced. The proportion of individuals moving into the subsurface decreased to 74% at 10% FS, and at 20% FS no individuals entered the sediments, supporting our hypothesis. These results demonstrate the importance of reducing FS inputs into river ecosystems and restoring FS-clogged riverbeds, to promote refuge use during increasingly common instream disturbances.
TL;DR: The results indicate that waterbird assemblage composition within Amazonian floodplains does result from links in processes operating at both spatial scales as predicted by neutral theory or influenced by local ecological factors as expected by niche theory.
Abstract: The main hypothesis is that waterbird richness in Amazonian lakes differs between white- and black-waters, and has gradients in species com- position relating to lake-to-lake differences in shape, depth, water transparency, habitat richness, and pro- ductivity. I tested a complementary hypothesis that bird assemblages respond to variations in lake char- acteristics over a regional scale, and to neighboring aquatic components, called water body richness, including rivers, channels, and ponds. Bird surveys were conducted by circumnavigating 70 lakes along 1,000 km of Amazon River floodplains. To test these hypotheses, a non-metric multiple-dimensional scal- ing ordination complemented by multiple linear models was used to determine relationships between bird richness and assemblage composition, and biotic and abiotic lake characteristics. At a local scale, lake shape, water transparency, and trophic status influence bird assemblages. At a regional scale, differences among sites in water body richness, produced by Amazon River tributaries, and the two water types, are determinants of variation in composition of waterbird assemblages. The results indicate that waterbird assemblage composition within Amazonian flood- plains does result from links in processes operating at both spatial scales as predicted by neutral theory or influenced by local ecological factors as predicted by niche theory.
TL;DR: In this article, the authors test the hypothesis that damming water courses exerts a negative effect on the zooplankton community by decreasing the alpha diversity, which is positively related to total phosphorus.
Abstract: Reservoirs are intermediate ecosystems between rivers and lakes. These ecosystems break up the landscape by forming artificial lakes connected by rivers and change important ecological processes of lotic ecosystems (e.g. organic matter production and nutrient cycling) and thus have direct effects on aquatic biodiversity. We test the hypothesis that damming water courses exerts a negative effect on the zooplankton community by decreasing the alpha diversity. Samplings were conducted in 30 reservoirs and 29 natural lakes in the Neotropics, during two hydrological periods (dry and rainy) in 2001. The study analysed differences in alpha diversity, the number of rare, accessory and constant species, and species composition between the types of lakes. Alpha diversity was significantly higher in natural lakes and species composition differed between natural lakes and reservoirs. Zooplankton alpha diversity was positively related to total phosphorus (best model), indicating that productive environments (natural lakes) gather more species. Our results suggest that reservoirs have negative effect on community structure, whereas natural lakes have an important ecological function for biodiversity conservation because they are refuges for biodiversity.
TL;DR: In this article, the authors evaluate the viability of the aluminum dosing hypothesis for six Danish lakes that received Al in a molar ratio of 2-3 years and conclude that if external Ploading is sufficiently low, lasting improvement of water quality can be obtained if Al is dosed 10:1 or higher relative to the size of the mobile P pool.
Abstract: If dosed sufficiently relative to the pool of excess phosphorus (P) in the lake sediment and lake water, aluminum (Al) is hypothesized to block sediment P release and thereby improve water clarity in eutrophic lakes. Aluminum has been used in >200 lakes worldwide, but in some 30% of the known cases water clarity did not improve beyond the first year, likely because of underdosing or continued high external P loading. We evaluate the viability of the aluminum dosing hypothesis for six Danish lakes that received Al in a molar ratio of 2–3 years) improvement of water clarity was only observed in two lakes. Sediment P release rates, which were measured in four lakes, declined significantly but then increased gradually again in the two lakes receiving the lowest doses. We conclude that if external P-loading is sufficiently low, lasting improvement of water quality can be obtained if Al is dosed 10:1 or higher relative to the size of the mobile P pool.
TL;DR: The differences in distribution patterns between species indicate that they are differently affected by the topographic barrier between the North Atlantic and the Nordic Seas, indicative of biogeographic provinces relevant to cold-water corals and their habitat requirements.
Abstract: The distribution of nine cold-water corals in the cold temperate North Atlantic is described based on existing records. The species studied are Lophelia pertusa, Madrepora oculata, Paragorgia arborea, Primnoa resedaeformis, Paramuricea placomus, Acanella arbuscula, Isidella lofotensis, Radicipes gracilis and Acanthogorgia armata. The compiled number of records were 5,854, of which 4,875 were obtained from databases and 979 from publications. Distribution maps were produced and temperature, broad-scale topography and current patterns were considered to understand the distribution patterns and conditions at which the species thrive. Currents connecting shelves and slopes above 500 m can explain the wide spatial distribution of L. pertusa, P. arborea and P. resedaeformis. However, L. pertusa is scarce on the western side of the North Atlantic, P. arborea has only few records off Iceland and A. arbuscula and A. armata are not found on the Norwegian shelf. The differences in distribution patterns between species indicate that they are differently affected by the topographic barrier between the North Atlantic and the Nordic Seas. Present knowledge of dispersal ability of cold-water corals does not allow a firm causal explanation to the observed distribution patterns. These, however, are indicative of biogeographic provinces relevant to cold-water corals and their habitat requirements.
TL;DR: It is suggested that future indices should consider including new metrics of functional and phylogenetic diversity to properly monitor multiple dimensions of biodiversity.
Abstract: The idea behind multimetric indices is to integrate information from several metrics to provide a general classification of water bodies without losing the particularities of each individual metric. Historically, multimetric indices use information on richness, taxon sensitivity, and taxonomic diversity. Recently, functional and phylogenetic diversity proved to capture different dimensions of biodiversity. Here we asked if these new metrics provide complementary information to classical metrics and should be included in multimetric indices. We used an index construction protocol based on statistical filters to test candidate metrics for range, sensitivity, and redundancy. We used macroinvertebrate data from streams located in a Savanna region of Brazil, encompassing a gradient of impact, to test our ideas. Of 41 candidate metrics, functional dispersion of functional diversity, mean nearest neighbor distance of phylogenetic diversity, and four classical metrics passed the filter selection composing the final multimetric index. Our results indicated that functional and phylogenetic diversity metrics indeed responded to environmental impact and complemented the information provided by classical metrics. We suggest that future indices should consider including new metrics of functional and phylogenetic diversity to properly monitor multiple dimensions of biodiversity.
TL;DR: The findings are consistent with the long-term presence of Bdelloidea in Antarctica, with their considerable isolation facilitating intraregional radiation, providing further evidence that does not support the microbial global ubiquity hypothesis that “everything is everywhere.”
Abstract: Antarctica is an isolated continent whose conditions challenge the survival of living organisms. High levels of endemism are now known in many Antarctic organisms, including algae, tardigrades, nematodes and microarthropods. Bdelloid rotifers are a key, widespread and abundant group of Antarctic microscopic invertebrates. However, their diversity, regional distribution and endemism have received little attention until recently. We provide the first authoritative review on Antarctic Bdelloidea, based on published data and new collections. Our analysis reveals the extreme levels of bdelloid endemism in Antarctica. Sixty-six bdelloid morphospecies are now confirmed from the continent, and 83–91 putative species are identified using molecular approaches (depending on the delimitation method used). Twelve previously unknown species are described based on both morphology and molecular analyses. Molecular analyses indicate that only two putative species found in Antarctica proved to be truly cosmopolitan. The level of endemism based on the available data set (95%) is higher than that in any other continent, with many bdelloid species occurring only in maritime or continental Antarctica. These findings are consistent with the long-term presence of Bdelloidea in Antarctica, with their considerable isolation facilitating intraregional radiation, providing further evidence that does not support the microbial global ubiquity hypothesis that “everything is everywhere.”
TL;DR: The hypothesis that the body size of cladocerans, calanoids, and cyclopoids declines with increasing water temperature is tested, and perhaps calanoid body size is not metabolically constrained by temperature or is differently affected by changes in fish predation occurring with increasing temperature.
Abstract: The body size of zooplankton has many substantive effects on the function of aquatic food webs. A variety of factors may affect size, and earlier studies indicate that water temperature may be a particularly important variable. Here we tested the hypothesis that the body size of cladocerans, calanoids, and cyclopoids declines with increasing water temperature, a response documented in an earlier study that considered only cladoceran zooplankton. We tested the hypothesis by comparing body size data that were available from prior studies of lakes ranging from 6 to 74o latitude and encompassing a temperature range of 2–30°C. Cladoceran body size declined with temperature, in a marginally significant manner (P = 0.10). For cyclopoids, the decline was more significant (P = 0.05). In both cases, there was considerably more variation around the regression lines than previously observed; suggesting that other variables such as fish predation played a role in affecting size. Calanoid body size was unrelated to temperature. In contrast with cladocerans and cyclopoids, perhaps calanoid body size is not metabolically constrained by temperature or is differently affected by changes in fish predation occurring with increasing temperature. The unexpected result for calanoids requires further investigation.
TL;DR: The trophic and spatial intra- and spatial inter-specific relationships established among native and salmonid species in a deep lake of Patagonia are analyzed to determine niche partitioning patterns as well as supporting the idea that native and non-native fishes could be avoiding negative interactions (e.g., competition) through trophics and spatial resource partitioning.
Abstract: Species introductions force sympatry between species that did not coevolve. Introduced salmonids have coexisted with native fish since the early 20th century in Patagonian water bodies, thus generating questions about the mechanisms that facilitate their coexistence. We analyzed the trophic and spatial intra- and inter-specific relationships established among native and salmonid species in a deep oligotrophic lake of Patagonia in order to determine niche partitioning patterns as strategies for their coexistence. Salmonids were more generalist feeders, while native species had narrower trophic niches. Native fish and introduced salmonids partitioned food, mainly through the consumption of the crayfish Samastacus sp. and the native galaxiid Galaxias maculatus, respectively. The diet of most species changed with body size, shifting from insects/amphipods to the larger G. maculatus and crayfish. Trophic interactions varied with season, in association with prey seasonality. In general, fishes feeding on the same prey were captured in the same depth strata, indicating common use of food and space. Our results provide new evidence on the trophic ecology of a mixed fish community (exotic-native), supporting the idea that native and non-native fishes could be avoiding negative interactions (e.g., competition) through trophic and spatial resource partitioning.