Insufficient oxygen delivery to tissues is hypothesised to limit thermal tolerance, but evidence in ectotherms is mixed. We assessed heat tolerance under hypoxia, normoxia and hyperoxia to test ...whether the extent in which oxygen can lower or increase heat tolerance differed with mode of respiration, comparing gill-breathing caenogastropods and lung-breathing pulmonates with or without an accessory gill. Hypoxia lowered heat tolerance in three of the four pulmonates (Physa fontinalis, Physa acuta and Planorbis carinatus) by 1.2–2.1°C. Hyperoxia, however, did not increase the heat tolerance in any of the pulmonate species. Thus, heat tolerance limits of these pulmonates does not appear to be oxygen limited under normoxia, possibly because of their high capacity to regulate oxygen consumption associated with aerial gas exchange. Instead, other processes may become limiting at thermal extremes such as loss of protein function, loss of membrane stability or neuronal dysfunction. The caenogastropod species tested (Potamopyrgus antipodarum, Bithynia tentaculata) closed their operculum during the warming experiments. This behavioural response prevented us from obtaining clear results. Nevertheless, our results suggested hyperoxia may increase heat tolerance in B. tentaculata. This could be related to its lower capacity to regulate oxygen, owing to its fully aquatic gas exchange mechanism.
Alternative Lengthening of Telomeres (ALT) is a telomere maintenance pathway utilised in 15% of cancers. ALT cancers are strongly associated with inactivating mutations in ATRX; yet loss of ATRX ...alone is insufficient to trigger ALT, suggesting that additional cooperating factors are involved. We identify H3.3
and IDH1/2 mutations as two such factors in ATRX-mutated glioblastomas. Both mutations are capable of inactivating histone demethylases, and we identify KDM4B as the key demethylase inactivated in ALT. Mouse embryonic stem cells inactivated for ATRX, TP53, TERT and KDM4B (KDM4B knockout or H3.3
) show characteristic features of ALT. Conversely, KDM4B over-expression in ALT cancer cells abrogates ALT-associated features. In this work, we demonstrate that inactivation of KDM4B, through H3.3
or IDH1/2 mutations, acts in tandem with ATRX mutations to promote ALT in glioblastomas.
Introductions of the invasive zebra mussel (
Dreissena polymorpha
) and quagga mussel (
Dreissena rostriformis bugensis)
into hydrologically isolated water bodies have been attributed to overland ...transport via (recreational) boat hulls. Before a boat becomes a successful vector, mussels must (1) attach to the hull, (2) survive air exposure during overland transport and (3) establish a viable population either after detachment or release of spat during launching or sailing. This study mimics these dispersal barriers and assesses the potential of boat hull-mediated release into a recipient environment for both species. Individuals were allowed to attach to aluminium and fibreglass plates. Hereafter, attached individuals were exposed to air and subsequently submerged again. Zebra mussels had a significantly higher attachment rate than quagga mussels. The percentage of attached dreissenid mussels that detached alive during rewetting ranged between 7.9 and 21.8%. No significant difference was found between species and hull materials. However, alive detachment during rewetting was significantly higher after 24 h compared to 48 h of air exposure. Our data allow modelling introduction pressure of lakes if quantitative data on overland boat movement and the density of attached mussels are available.
Since its appearance in 2006 in a freshwater section of the Rhine–Meuse estuary (Hollandsch Diep, The Netherlands), the non-indigenous quagga mussel has displayed a rapid range expansion in Western ...Europe. However, an overview characterising the spread and impacts of the quagga mussel in this area is currently lacking. A literature study, supplemented with field data, was performed to gather all available data and information relating to quagga mussel dispersal. Dispersal characteristics were analysed for rate and direction and in relation to hydrological connectivity and dispersal vectors. To determine ranges of conditions suitable for quagga mussel colonisation, physico-chemical characteristics of their habitats were analysed. After its initial arrival in the freshwater section of the Rhine-Meuse estuary and River Danube, the quagga mussel demonstrated a rapid and continued range expansion in Western Europe. Quagga mussels have extended their non-native range to the network of major waterways in The Netherlands and in an upstream direction in the River Rhine (Germany), its tributaries (rivers Main and Moselle) and the River Meuse (Belgium and France). The calculated average quagga mussel dispersal rate in Europe was 120 km year
−1
(range 23–383 km year
−1
). Hydrological connectivity is important in determining the speed with which colonisation occurs. Dispersal to water bodies disconnected from the freshwater network requires the presence of a suitable vector e.g. pleasure boats transferred over land. Upstream dispersal is primarily human mediated through the attachment of mussels to watercraft. The relative abundance of quagga mussel to zebra mussel has greatly increased in a number of areas sampled in the major Dutch rivers and lakes and the rivers Main and Rhine and the Rhine–Danube Canal leading to a dominance shift from zebra mussels to quagga mussels. However, evidence for displacement of the zebra mussel is limited due to the lack of temporal trends relating to the overall density of zebra and quagga mussel.
Summary
Laboratory data on desiccation tolerance of native and non‐native mollusc species were used to derive species sensitivity distributions (SSDs), to predict effects of desiccation on mollusc ...assemblages in rivers during low discharge events and to prioritise various environmental stressors (i.e. desiccation, temperature and salinity).
The predicted absence and observed absence of mollusc species by desiccation at a specific site were expressed as potentially not occurring fraction (PNOF) and not occurring fraction (NOF) of their regional species pool in the River Rhine.
Calculations of PNOFs for desiccation explained 57% (LT99) and 65% (LT50) of the NOFs of the mollusc species. Sensitivity to desiccation did not differ between native and non‐native mollusc species pools.
Due to differences in frequency of low river discharge events and water level fluctuations, mollusc species in an impounded reach of the River Meuse were less affected by desiccation than in a free‐flowing distributary of the River Rhine.
Earlier calculations of the PNOFs for combined effects of temperature and salinity in the River Rhine explained 22 and 3% of the NOFs of native and non‐native species, respectively, for the period 1988–2003. Accounting for the effects of desiccation, 62 and 80% of the NOFs of the native and non‐native species pool, respectively, were explained, indicating that desiccation during low discharge events was an important stressor in comparison with water temperature or salinity.
Since a relatively high percentage of the NOFs of native species in the River Rhine still remain unexplained, an effort to assess potential effects of other stressors is recommended (e.g. toxic substances or water turbulence caused by commercial shipping).
Longitudinal training dams (LTDs) in the river Waal are novel river training structures that protect the littoral zone from the adverse effects of navigation providing new habitats for riverine ...macroinvertebrates. In order to inform river management and to better understand their ecological value for native and alien mussel species, it is important to assess the habitat suitability of the protected LTD shore channels. We applied spatial hydroacoustics surveys consisting of side-scan sonar (SSS) and acoustic Doppler current profiler (ADCP) of the substrate type, water depth and flow velocity in three shore channels in combination with species sensitivity distributions (SSDs) to predict habitat suitability for native and alien mussel species. SSDs allowed for the prediction of habitat suitability as a potentially occurring fraction (POF) of a species pool. High substrate type, water depth, and near-bottom flow velocity POFs were found for ≥ 70%, 100%, and 4–51% of the total shore channel area, respectively, suggesting that shore channels provide suitable habitat for both native and alien mussel species. To enhance the shore channels as habitat for native mussel species, we recommend increasing shallow areas dominated by fine (silt/clay) and sand substrate types with low near-bottom flow velocities (near 0 m/s). In contrast, the total area of hard substrate (e.g., boulders) in the shore channels should be reduced as it strongly favored invasive alien mussel species in our study. Future research should include additional abiotic parameters to enhance the habitat suitability predictions and compare the results for different riverine habitats.
Longitudinal training dams (LTDs) are novel hydraulic engineering structures in the river Waal intended to facilitate intensive navigation and safe discharges in the main channel while providing ...sheltered habitats for aquatic biota in shore channels. Monitoring data collected using light detection and ranging, multibeam echosounder and aerial photography for the years during and after the construction of the LTDs were analysed in order to determine patterns of erosion and deposition, the retreat rate of steep eroding banks and shoreline length change through time. The LTD shore channels and two traditional groyne fields (references) were divided into nine mesohabitats based on physical attributes. Net erosion was estimated for eight out of the nine mesohabitats for the 2015–2020 period. Generally, there was a pattern of riverbed aggradation towards the LTDs and degradation or bank erosion towards the littoral zones of the LTD shore channels. This kind of continuous behaviour could be indicative of current or eminent channel and thus habitat stability. The bankline erosion in shore channels had mean retreat rates of 1.4–1.6 m/year. The shorelines were longer in sand‐dominated mesohabitats, which could be key for habitat heterogeneity. The LTD shore channels offered more complex relatively natural continuous littoral zones than the traditional groyne fields while maintaining the multifunctionality of the river. Thus, the development of sandy shorelines in the LTD shore channels should be encouraged through management in order to enhance biodiversity. Geomorphological monitoring of the shore channels should continue in the future in order to detect any long‐term changes in the sedimentary processes and ecological functions.
Longitudinal training dams (LTDs) are novel hydraulic engineering structures in the river Waal intended to facilitate intensive navigation and safe discharges in the main channel while providing sheltered habitats for aquatic biota in shore channels. Net erosion was estimated for eight out of the nine mesohabitats for the 2015‐2020 period. The LTD shore channels offered more complex, relatively natural continuous littoral zones than the traditional groyne fields while maintaining the multifunctionality of the river.
Riverine macroplastic pollution (>0.5 cm) negatively impacts ecosystems and human livelihoods. Monitoring data are crucial for understanding this issue and for the design of effective interventions ...strategies. Macroplastic pollution floating on the river surface and plastic deposited on riverbanks are studied relatively often. Data on riverine plastics in the water column remain scarce. In this study, we utilized trawl nets at different depths to sample plastic pollution in the water column at the entry point of the river Rhine to the Netherlands. We show that plastic concentrations in the water column increased during higher discharge. Moreover, the results indicate that the vertical distribution of macroplastic pollution changes during different flow conditions. Significantly higher concentrations of macroplastic can be seen near the riverbed during low discharge conditions, while no significant differences in concentration are observed between the bottom, middle, and surface samples during high discharge conditions. Taking into account the recurrence time of low discharge conditions the transport of plastic during low discharge conditions is substantial. These findings provide first insights into the key role of hydrology in explaining macroplastic transport in the water column. These insights can be used to improve future monitoring and intervention strategies.
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•Macroplastic (>0.5 cm) pollution in the water column was sampled with a novel method at the entry point of the river Rhine to the Netherlands•Macroplastic concentrations increased with higher discharge levels•Vertical macroplastic distributions changed with higher discharge, likely due to increased vertical mixing
Although studies on plastic concentrations mainly focus on the marine environment, recently, an increasing number of studies point out environmental consequences in freshwater environments around the ...world. However, there still is a paucity of field data on the abundance of riverine plastic items, in particular in the water column. In this study, we provide an overview of macro- and mesoplastic concentrations, categories, ages, and origin over several years in the water column of the river Waal, in the Netherlands. The river water column was passively sampled at two selected locations using a stow net at very low and low discharges (range 537 - 1345 m3.s−1). The most dominant macro- and mesoplastic categories were ‘Miscellaneous plastic waste’, including “Plastic film 2.5 - 50 cm (soft)” and “Plastic film 0 - 2.5 cm (soft)” as main categories. Macro- and mesoplastic categories were found to show limited variability during several years of monitoring. The mean macroplastic concentration (± SD) ranged between 2.2 × 10−3 ± 0.001 and 7.4 × 10−3 ± 0.003 particles.m−3 for October 2020 and November 2018, respectively. In 2020, the plastic concentrations showed a sharp decrease compared to the previous years, most likely as a consequence of the COVID-19 crisis. The origin of the plastics (e.g., countries) also showed little variability during monitoring. The consistency of several characteristics of the collected plastic suggests that the same sources were responsible for the macro- and mesoplastic input into the river Waal during low discharges and over multiple years. We present the first temporal assessment of macro- and mesoplastic concentrations and composition in the water column of the river Waal. The outcome of the current study can be used to support the development of management measures by decision makers.
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•12,832 plastic items were collected during monitoring campaigns.•“Plastic film (soft)” was the most dominant macroplastic and mesoplastic category recorded.•Inland shipping is a relevant source of plastic pollution in the freshwater environment.•Under low flow conditions concentrations and composition showed a limited temporal variability.
Invasive alien species (IAS) are species whose introduction or spread outside their native range threatens biological diversity, ecosystem functioning, economy, and/or public health. The recent ...European Union (EU) regulation on the management of IAS emphasizes the need for a consistent approach to alien species assessment that will underpin international measures for the early identification of newly introduced IAS followed by rapid action aimed at the prevention of introduction, spread, and negative impacts. The goals of the present study were (1) to present the risk classifications of 18 aquatic alien species for The Netherlands using the Invasive Species Environmental Impact Assessment protocol, (2) to compare these with available risk classifications made for countries spanning similar climatic and biogeographical regions to the EU, and (3) to provide explanations for inconsistencies between different risk classifications. Five species were classified as high risk: Carassius gibelio (Prussian carp), Cyprinus carpio (common carp), Sander lucioperca (pike‐perch), Cabomba caroliniana (fanwort), and Dreissena rostriformis bugensis (quagga mussel). Of the 14 species with existing risk classifications for countries spanning similar climatic and biogeographical regions to the EU, all but two of the assessed species (C. gibelio and D. rostriformis bugensis) were classified inconsistently. Reasons for these inconsistencies are the application of different risk assessment schemes, application on a national rather than biogeographical scale, differences in the definition and application of criteria, differences in habitat availability, and uncertainties that are intrinsic to risk assessment methodologies. Approaches that increase transparency by highlighting these methodological aspects, normative choices, and uncertainties are vital to the legitimacy of any risk assessment method and will increase acceptance among decision makers, nature managers, and stakeholders.
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