Juergen Geist

• Prof. Dr. rer. nat.
• Chair at Technical University of Munich

In one of the largest floodplain forests in Germany along the straightened and dammed river Danube between Neuburg and Ingolstadt, restoration actions were completed in 2010. They consisted of 1) a new 8 km long floodplain stream with dynamic water diversion, 2) ecological flooding and 3) groundwater draw down at low water in the Danube. The MONDAU...

Background Antibiotics and antiparasitics are essential tools in controlling infectious disease outbreaks in commercial aquaculture. While the negative effects of antimicrobials on the gut microbiome of various farmed fish species are well documented, the influence of underlying host factors, such as age, on microbiome responses remains poorly unde...

Plastic pollution by lost, abandoned and discarded commercial fishing gear is well characterized for marine systems, whereas the environmental impact of lost recreational fishing gear in freshwater systems remains unclear. Especially soft plastic lures are increasingly used, potentially contributing to the pollution of waterbodies by the release of...

The Portuguese oyster, Crassostrea angulata, is an important aquaculture bivalve species in Asia, where it is native. This study was carried out to estimate genetic parameters for shell growth and survival over six generations of selection based on harvest whole weight. The phenotypic measurements including shell height and length, and survival rat...

This study investigated the predatory behavior of northern pike in response to trolling with natural and artificial baits using underwater cameras. Predator types of 32 captured pike were identified based on their coping style under altered environmental conditions by measuring latency to forage in individual novel net enclosures. Fast-attacking pi...

Rivers and their fish populations are under threat, prompting diverse conservation efforts. Effective freshwater conservation requires collaborative projects involving multiple stakeholders, including scientists, practitioners, and government agencies. Knowledge produced in these projects can be used to guide the application of evidence‐based conse...

Adaptive divergence and increased genetic differentiation among populations can lead to reproductive isolation. In Lake Constance, Germany, a population of invasive three-spined stickleback (Gasterosteus aculeatus) is currently diverging into littoral and pelagic ecotypes, which both nest in the littoral zone. We hypothesized that assortative matin...

Animal growth is a fundamental component of population dynamics, which is closely tied to mortality, fecundity, and maturation. As a result, estimating growth often serves as the basis of population assessments. In fish, analysing growth typically involves fitting a growth model to age‐at‐length data derived from counting growth rings in calcified...

The return of beavers to the strongly structurally altered Central European stream systems results in a variety of conflicts, potentials and opportunities. Among monetary compensation issues for landowners, target species conflicts with fish conservation remain unresolved. This work investigated the impact of beaver structures of the Eurasian beave...

The restoration of rivers and their floodplains is complex, requires substantial financial efforts, intensive stakeholder involvement and long recovery times, making the identification of appropriate ecological indicators for restoration success a key challenge. Herein, one of the largest floodplain restorations along the European Danube was repeat...

Freshwater organisms are among the most vulnerable species being impaired by global climate change. Freshwater Pearl Mussel (Margaritifera margaritifera) is a keystone species that facilitates a number of important ecosystem functions in cold water oligotrophic streams, while is currently facing habitat alteration and degradation due to human activ...

The two highly endangered European mussel species Margaritifera margaritifera and Unio crassus are target species of conservation. Based on a recently completed systematic statewide monitoring of each 22 M. margaritifera and 22 U. crassus streams in Bavaria, Germany, we present an update on population trends, conservation status, habitat quality an...

Originating from the Black and Caspian seas, the Round Goby (Neogobius melanostomus) has become one of the most successful invaders of freshwater ecosystems. In this study, we provide a characterization of the reproductive strategy of an established population of Round Gobies in the Upper Danube river including sex ratio, fluctuations of gonadosoma...

Zusammenfassung In der vorliegenden Studie wurden über einen Zeitraum von 10 Jahren neun Wasserkraftanlagen mit unterschiedlichen innovativen und konventionellen Kraftwerkstechnologien hinsichtlich ihrer direkten Auswirkungen auf passierende Fische (z. B. Mortalität und Verletzungen) und ihrer Auswirkungen auf den Lebensraum und die Zusammensetzung...

The increase in the frequency and intensity of droughts and heatwaves caused by climate change poses a major threat to biodiversity. In aquatic systems, sedentary species such as freshwater mussels are generally considered more vulnerable to changes in habitat conditions than mobile species such as fish. As mussels provide important ecosystem servi...

Connectivity between terrestrial and aquatic systems is a prerequisite of effective blue-green infrastructure (BGI). Anthropocentric human activities including the transportation network are the main reasons behind BGI fragmentation. Yet, identifying and mitigating this fragmentation is possible. In this study we aim to assess the current situation...

The waterfront connects aquatic and terrestrial habitats, and its landscape quality is an indicator of the status of blue-green infrastructure. Especially in urban areas, the consequences of direct human interventions on the waterfront are evident, yet there is a need for more comprehensive and easy approaches to quantify the dynamics of the waterf...

This study elucidates to generate a linkage map for Portuguese oysters, Crassostrea angulata, and recognise potential markers linked to economical traits in C. angulata. Genome-wide association studies (GWAS) using 19,475 single nucleotide polymorphisms (SNPs) generated by a genotyping-by-sequencing approach consisting of 647 individuals in two sel...

The European catfish (Silurus glanis) is a large apex predator native to Eastern Europe. Increasing populations within and outside the species’ native range in recent years, and its popularity with recreational anglers are fueling discussions about appropriate management. To understand the motivations of anglers and their views on different managem...

Background Freshwater mussels are important keystone and indicator species of aquatic ecosystems. Recent advances in sensor technology facilitate applications to individually track mussels and to record and monitor their behavior and physiology. These approaches require the attachment of sensor devices as “backpacks” to the outer shell surface. The...

In the original publication [...]

Floods, droughts, and heatwaves are increasing globally. This is typically attributed to CO2-driven climate change. However, at the global scale, CO2-driven climate change neither reduces precipitation nor adequately explains droughts despite the modest increase in evapotranspiration due to temperature rise. Past land-use changes, particularly soil...

The Longfin Smelt (LFS, Spirinchus thaleichthys) population within the San Francisco Estuary, California, has experienced a substantial reduction, diminishing to <1% of their historical abundance. This decline has culminated in their classification as a threatened species under the purview of the California Endangered Species Act. Understanding the...

The inheritance of historic human-induced disruption and the fierceness of its impact change aquatic ecosystems. This work reviews some of the main stressors on freshwater ecosystems , focusing on their effects, threats, risks, protection, conservation, and management elements. An overview is provided on the water protection linked to freshwater st...

The inheritance of historic human-induced disruption and the fierceness of its impact change aquatic ecosystems. This work reviews some of the main stressors on freshwater ecosystems, focusing on their effects, threats, risks, protection, conservation, and management elements. An overview is provided on the water protection linked to freshwater str...

Micro- and nano-plastics are pervasive pollutants in global ecosystems, yet their interactions with aquatic wildlife and abiotic factors are poorly understood. These particles are recognized to cause subtle detrimental effects, underscoring the necessity for sensitive endpoints in ecotoxicological exposure studies. We investigated the effects of pa...

Water surface roughness (SR) is a highly relevant parameter governing data reliability in remote sensing applications, yet lacking appropriate methodology in riverine habitats. In order to assess thermal accuracy linked to SR of thermal imaging derived from an unmanned aerial vehicle (UAV), we developed the SR Measurement Device (SRMD). The SRMD us...

Across many ecosystems in North America and Europe, native freshwater bivalves (Order Unionida) are threatened by fouling and competition for food by the invasive zebra mussel Dreissena polymorpha. In light of climate change, knowledge on the influence of water temperature on these competitive effects is important, yet poorly understood. This study...

Preventing fish entrainment during their downstream passage at hydropower plants remains a major challenge in reducing the ecological impacts of hydropower production. We investigated fish behavior at the world's first innovative shaft hydropower plant with its novel screen concept, aiming at reducing fish entrainment due to the fully horizontal ar...

Ecosystem services (ES) are essential to sustainable development at multiple spatial scales. Monitoring ES potential (ESP) at the metropolitan level is imperative to sustainable cities. We developed a procedure for long-term monitoring of metropolitan ESP dynamics, utilizing open-source land use land cover (LULC) data and the expert matrix method....

Science education often aims to increase learners’ acquisition of fundamental principles, such as learning the basic steps of scientific methods. Worked examples (WE) have proven particularly useful for supporting the development of such cognitive schemas and successive actions in order to avoid using up more cognitive resources than are necessary....

The interface between groundwater and surface water is a critical zone influencing ecohydrological and biogeochemical cycles within surface water ecosystems. It is characterized by complex redox gradients, with groundwater-mediated inflow of reduced substances affecting the oxygen budget of stream water. In this study, we have experimentally simula...

The global decline of freshwater mussels and their crucial ecological services highlight the need to understand their phylogeny, phylogeography and patterns of genetic diversity to guide conservation efforts. Such knowledge is urgently needed for Unio crassus, a highly imperilled species originally widespread throughout Europe and southwest Asia. R...

This study investigates the effect of large woody debris (LWD) on the abundance of juvenile Atlantic salmon (Salmo salar, L.) and anadromous brown trout (Salmo trutta, L.) in semi-alluvial side channels of the river Aurlandselva (Norway) using point electrofishing and microhabitat mapping. Not the presence of LWD, but stream bed shelter availabilit...

Ecological assessments of the effects of hydropower plants (HPPs) are often limited to aspects of entrainment, mortality, injuries, and passage of fish, whereas the effects on riverine habitats and biological communities in proximity to these structures are hardly documented. In this study, aquatic communities comprising fish, macroinvertebrates, m...

Longer durations of warmer weather, altered precipitation, and modified streamflow patterns driven by climate change are expected to impair ecosystem resilience, exposing freshwater ecosystems and their biota to a severe threat worldwide. Understanding the spatio-temporal temperature variations and the processes governing thermal heterogeneity with...

Successful aquatic biological invasions are often dependent on human vectors. The Chinese pond mussel Sinanodonta woodiana is a fast-growing , high-filtering, and highly fecund unionid bivalve that has expanded rapidly throughout Europe in the last several decades. Human-mediated vectors such as fish aquaculture and pet shop trade are believed to b...

Im Rahmen des durch Deutschland erstellten Aktionsplans der Verordnung (EU) Nr. 1143/2014 sind Maßnahmen für 14 prioritäre Pfade festgelegt worden, die die nicht vorsätzliche Einbringung und Ausbreitung invasiver gebietsfremder Arten verhindern sollen. In der vorliegenden Machbarkeitsstudie wurden auf Basis einer umfassenden Literaturrecherche und...

Although scientific research has identified the causes of undesirable ecological changes in fresh waters, translating the results of research into practical conservation and management, and raising awareness of the need for action, is often inadequate. This Viewpoint considers the present coverage of conservation‐related freshwater research, the ap...

Fatty acids, and especially long‐chain polyunsaturated fatty acids, are biologically important components in the metabolism of vertebrates, including fish. Essential fatty acids (EFA) are those that in a given animal cannot be synthesized or modified from precursors and must therefore be acquired via the diet. Because EFAs are often unevenly distri...

Aquaculture mollusc production is predominantly from Asia, with more than 80% of the total biomass produced in China. Vietnam’s annual mollusc production is growing rapidly but is comparatively small given its coastal resources. A significant challenge for future mollusc production, and oysters in particular, is the supply of high-quality spat. Mos...

In the context of the European Union (EU) Drinking Water Directive, freshwater mussels (Order Unionoida: Bivalvia) can help us face the challenges of safe drinking water provisions for all citizens in the EU. Specifically, the implementation of high frequency noninvasive (HFNI) valvometers allows the early detection of eventual pollution events in...

The hyporheic zone (HZ) is of major importance for carbon and nutrient cycling as well as for the ecological health of stream ecosystems, but it is also a hot spot of greenhouse gas production. Biogeochemical observations in this ecotone are complicated by a very high spatial heterogeneity and temporal dynamics. It is especially difficult to monito...

Predictions of stream water temperature are an important tool for assessing potential impacts of climate warming on aquatic ecosystems and for prioritizing targeted adaptation and mitigation measures. Since predictions require reliable baseline data, we assessed whether open‐access data can serve as a suitable resource for accurate and reliable wat...

This study investigated how northern pike with two behavioral strategies in the context of predation interact with natural and artificial baits in simulated angling experiments. Predator types were assessed in three behavioral trials over 15 days by measuring foraging latency under altered conditions (abruptly increased light intensity). Latency re...

1. Freshwater mussels are declining throughout their range. Their important ecological functions along with insufficient levels of natural recruitment have prompted captive breeding for population augmentation and questions about the usefulness and applicability of such measures. 2. This article reviews the current state of captive breeding and r...

Efforts to increase the share of renewable energies and to reduce the negative ecological impacts of hydropower use are driving the development of novel hydropower technologies. Innovative hydropower concepts and turbine types should cause less fish damage and be more 'eco-friendly' than conventional hydropower plants. In this study, extensive ecol...

Freshwater fish populations are in steep decline, prompting conservation measures and a need for their evaluation. Fish are increasingly monitored with passive integrated transponders (PIT), although the suitability of this tagging technique has not yet been validated for most European target species of conservation. Consequently, this study tested...

The African Niger Delta is among the world's most important wetlands in which the ecological effects of intensive oil exploitation and global change are not well documented. We characterized the seasonal dynamics and pollution with total-petroleum-hydrocarbons (TPHs), heavy-metals (HMs) and nutrient-loads in relation to climate-driven variables. Hi...

The African Niger Delta is among the world's most important wetlands in which the ecological effects of intensive oil exploitation and global change are not well documented. We characterized the seasonal dynamics and pollution with total-petroleum-hydrocarbons (TPHs), heavy-metals (HMs) and nutrient-loads in relation to climate-driven variables. Hi...

Cyanobacteria are favored by climate change and global warming; however, to date, most research and monitoring programs have focused on planktic cyanobacteria. Benthic cyanobacteria blooms also increase and pose a risk to animal and human health; however, there is limited knowledge of their occurrence, distribution and the toxins involved, especial...

Functional and oxygenated stream beds provide crucial habitat for multiple endangered stream taxa, including endangered freshwater mussels, fishes, and insect larvae. Stream bed restoration measures such as substrate raking are often applied to mitigate excess fine sediment introductions and stream bed colmation, yet such measures are controversial...

Connectivity among blue-green infrastructure (BGI) is a vital condition for enhanced ecosystem services provision in metropolitan regions where the social-ecological systems are interwoven. In this study, we conduct a comparative spatial assessment of transversal connectivity of natural surfaces to freshwater sources for the metropolitan areas of B...

Climate change threatens freshwater fish species due to predicted changes in thermal, sedimentary and hydrological properties of stream ecosystems. Gravel-spawning fish are particularly sensitive to such alterations as warming, higher inputs of fine sediment and low-flow all have potentially negative effects on the functionality of their reproducti...

The hyporheic zone (HZ) is of major importance for carbon and nutrient cycling as well as for the ecological health of stream ecosystems. However, biogeochemical observations in this ecotone are complicated by a very high spatial heterogeneity and temporal dynamics. Especially the latter are difficult to observe without disturbing the system. In th...

The main goal of TransConnECT is to prove the indispensability of transversal connectivity for an enhanced multi-functional blue-green infrastructure (BGI) in metropolitan areas. Thus, the freshwater surfaces become not only vital urban biodiversity hubs but also components of nature-based flood management systems. TransConnECT aims to achieve an E...

Invasive “game-changer” species cause severe ecological impacts such as “phase shifts” in recipient ecosystems all over the world. Since the early 1990s, the ongoing global spread of the small but highly invasive Ponto-Caspian round goby Neogobius melanostomus into diverse freshwater and marine ecosystems has been observed. We postulate that this s...

Introduction: Hydropower plants are frequently equipped with physical and behavioral fish protection barriers to prevent downstream moving fish from harmful turbine passage and to guide them to alternative bypasses. As not only diadromous but also potamodromous fish species migrate and inevitably have to pass hydropower plants, knowledge on corrido...

Originally, the Danube salmon (Hucho hucho) occurred in Bavaria and Austria in more than 250 rivers occupying more than 7,400 km of rivers. Nowadays, populations in »very good« and »good« status exist in only 0.7 % and 7.1 % of the original distribution. Therefore, the Danube salmon is classified as an endangered species. Due to ongoing stock decli...

Local environments such as soils and waterways, but also landscape-scale environments such as agricultural areas, are often classified as oxic based on the dominant conditions in such systems. Still, anoxic conditions do occur within these "oxic" landscapes, their upland and lowland soils, sediments and creeks at a wide range of spatiotemporal scal...

Groundwater-influenced ditches, so called hinterland drainage systems (HDS), accompany many heavily modified water bodies (HMWBs). Herein, we evaluate the usefulness of including HDS as functional habitats in river restoration approaches by assessing their role as salmonid recruitment areas in HMWBs. We tested the functionality of spawning grounds...

Groundwater-influenced ditches, so called hinterland drainage systems (HDS), accompany many heavily modified water bodies (HMWBs). Herein, we evaluate the usefulness of including HDS as functional habitats in river restoration approaches by assessing their role as salmonid recruitment areas in HMWBs. We tested the functionality of spawning grounds...

Freshwater bivalves are key faunal elements of aquatic ecosystems. Native species declines are paralleled by increasing distribution and abundances of non-native species. Appropriate management of both groups depends on knowledge of their interactions, which remains limited. Herein, we systematically review the current knowledge status of native an...

Mitigating the adverse ecological impacts on stream ecosystems caused by hydropower expansion is a major challenge. To prevent fish from turbine entrainment and to reduce injury and mortality risk, physical barriers such as fine screens with horizontally or vertically oriented bars are frequently installed at turbine inlets. In this study, the spec...

This study analysed diversity patterns of sedimentary, littoral and planktic diatoms in 43 mountain lakes in the northern European Alps and identified processes that contribute to these patterns. Linear regression models showed a significant increase of sedimentary α -diversity with lake area and conductivity and a negative trend with increasing el...

We identified 14 emerging and poorly understood threats and opportunities for addressing the global conservation of freshwater mussels over the next decade. A panel of 17 researchers and stakeholders from six continents submitted a total of 56 topics that were ranked and prioritized using a consensus-building Delphi technique. Our 14 priority topic...

Environmental pollution by lost fishing tackle is hardly considered in freshwater management. We collected and classified lost angling tackle during the dewatering of Lake Eixendorf, Germany. Based on the results, 1 item per 100 m² lake area was found, resulting in 5442 items, with an overall weight of more than 65 kg. This included more than 5 km...

Europe has a long history of human pressure on freshwater ecosystems. As pressure continues to grow and new threats emerge, there is an urgent need for conservation of freshwater biodiversity and its ecosystem services. However, whilst some taxonomic groups, mainly vertebrates, have received a disproportionate amount of attention and funds, other g...

Aquaculture supplies 90% of demand for farmed fish, where 60% are freshwater fish. Here in Europe brown trout (Salmo trutta) plays a major role. To a significant extent, aquaculture depends on sustainable management, adequate water quality and prevention of diseases. As a consequence often veterinary drugs including antibitotics are often applied i...

Conservation of endangered, cold-stenothermic species, such as the freshwater pearl mussel (FPM) and its salmonid host fish, are particularly challenging in headwater streams as their last refuge areas. Understanding the impact of anthropogenic catchment features such as fish ponds on the hydrology and the temperature regime of such streams is, the...

The freshwater biodiversity decline affects all trophic levels, prompting restoration efforts. While habitat restoration for fish is well‐studied, habitat restoration to benefit other sensitive taxa such as Ephemeroptera, Plecoptera, and Trichoptera (EPT) remains poor. Consequently, this study investigated the habitat function of a man‐made nature‐...

Supportive breeding programmes are becoming increasingly crucial for the conservation of many declining freshwater fishes such as the European common nase, Chondrostoma nasus . However, small relict populations are genetically highly vulnerable, and supportive breeding can have a detrimental impact on the genetic composition of the cultured offspri...

Population recruitment of endangered rheophilic fish species strongly depends on the survival of critical egg and larvae life stages. However, the transportation and fate of eggs after spawning is not well understood. This study analyzed the egg transport and settling patterns of the endangered European nase (Chondrostoma nasus L.), testing the tra...

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...

Although the costs of fish-related mitigation measures can play an important role in the adoption of mitigation measures, there is relatively little information about this aspect. This chapter presents an overview of the range of costs for different mitigation measures and compares their magnitudes. As many mitigation measures are adopted in combin...

This chapter very briefly outlines site and constellation specific direct and indirect impacts of a hydropower scheme primarily on fishes. It describes potential effects of single elements of a hydropower scheme, such as available migration routes up- and downstream, impoundment, hydraulic head, turbine type and mode of operation. It summarises the...

Resolving the controversy about hydropower is only possible based on reliable data on its ecological effects, particularly fish welfare. Herein, we propose a comprehensive assessment of conventional and innovative hydropower using a dataset of 52,250 fish. The effects of hydropower on fish were most harmful at sites with Kaplan turbines, showing ≤8...

In context of transitioning towards renewable energy, hydroelectricity has gained global relevance. However, hydropower plants have severe impacts on aquatic habitat and biota: Dams disrupt migration routes of diad-romous and potamodromous fish species, degrade the hydro-morphology of streams and turbines cause high mortalities in fishes. To suppor...

The Chinese pond mussel, Sinanodonta woodiana, is non-native to European freshwater systems. Originating from Asia, it was brought to Europe in the 1970s and is now spreading across many countries. Management of the species is currently limited by a lack of information on the actual distribution and population characterisation of S. woodiana as wel...

The abundance and persistence of plastic nanoparticles in aquatic habitats are considered a threat to marine and freshwater biota. However, the risk assessment of plastic particles is complicated due to various factors that need to be considered, including composition, size and environmental abundance. This study investigated the behavioural respon...

The effects of microplastics on plants and animals have not yet been fully described. Microplastics have different properties that determine whether and how they are taken up by living organisms and the extent to which they are harmful to them. Compared to other pollutants in the environment, microplastics may therefore have a more complex effect o...

Incidents with toxic benthic cyanobacteria blooms have been increasing recently. In 2019, several dogs were poisoned in the river Lech (Germany) by the benthic anatoxin-a-producing genus Tychonema. To characterize spatial and temporal distribution of potentially toxic Tychonema in this river, a systematic monitoring was carried out in 2020, focusin...