Biodiversity conservation and management in urban aquatic ecosystems is crucial to human welfare, and environmental DNA (eDNA)-based methods have become popular in biodiversity assessment. Here we ...report a highly overlooked source of significant false positives for eDNA-based biodiversity assessment in urban aquatic ecosystems supplied with treated wastewater - eDNA pollution originating from treated wastewater represents a noteworthy source of false positives. To investigate whether eDNA pollution is specific to a certain treatment or prevalent across methods employed by wastewater treatment plants, we conducted tests on effluent treated using three different secondary processes, both before and after upgrades to tertiary treatment. We metabarcoded eDNA collected from effluent immediately after full treatment and detected diverse native and non-native, commercial and ornamental fishes (48 taxa) across all treatment processes before and after upgrades. Thus, eDNA pollution occurred irrespective of the treatment processes applied. Release of eDNA pollution into natural aquatic ecosystems could translate into false positives for eDNA-based analysis. We discuss and propose technical solutions to minimize these false positives in environmental nucleic acid-based biodiversity assessments and conservation programs.
•We detected eDNA pollution in treated wastewater released into natural waters.•eDNA contamination in treated effluent was common across popular processes.•Numerous commercial and ornamental fish were recovered from treated effluent.•eDNA pollution can lead to false positives in biodiversity assessment.•We proposed technical solutions for eDNA pollution-derived false positives.
The Great Lakes‐St Lawrence River basin is the world's most invaded freshwater system. Ballast water release from transoceanic shipping is deemed responsible for 65% of invasions in the basin since ...the modern St. Lawrence Seaway opened in 1959. Regulations requiring mid‐ocean exchange of ballast water applied in 1993 failed to stem ship‐mediated invasions because the procedure was not mandated for all ships. In 2006 and 2008, Canada and the United States, respectively, mandated that all transoceanic ships should conduct open ocean flushing to ensure that partially filled ballast tanks intended for discharge into the Great Lakes contained water of salinity ≥30 ppt before entering the Seaway. These regulations have been strictly enforced through record inspections and tests of ballast tank salinities of inbound ships. Before‐and‐after comparisons of total organismal abundance and species richness in ballast tanks revealed a substantial reduction in invasion risk from ships that conducted saltwater flushing. Since 2006, the rate of discovery of newly established non‐native species in the Great Lakes declined by 85% to its lowest level in two centuries. While multiple factors could plausibly contribute to this decline, empirical evidence supports the 2006/2008 ballast water regulation as the primary cause, highlighting the benefit of internationally coordinated vector control.
During the past three decades, coastal marine waters have become among the most invaded habitats globally. Ascidians are among the most notorious invaders in these ecosystems. Owing to their rapid ...spread, frequent population outbreaks, and associated negative ecological and economic impacts, invasive ascidians have become a global problem. Thus, the study of ascidian invasions has become a prominent area of invasion biology. Here, we review current knowledge and conclude that ascidians are good models for studying invasion success in the marine realm. Firstly, we summarize the reconstruction of invasion pathways or colonization histories and associated negative impacts of invasive ascidians, and address the urgent need to clarify ambiguous taxonomy of ascidians. Secondly, we discuss factors that underlie or facilitate invasion success of ascidians, including vectors of introduction and spread, environmental changes, biological traits, and possible genetic issues. Finally, we summarize current science-based policies and management solutions that are in place to prevent and control spread of invasive ascidians. We conclude by highlighting key research questions that remain to be answered, and propose future research to investigate mechanisms of invasion success in the marine realm using ascidians as model systems.
Ballast water is recognized as a leading pathway for the introduction of aquatic non‐indigenous species which have caused substantial ecological damage globally.
Following international regulations, ...most international ships will install a ballast water management system (BWMS) by 2024 to limit the concentration of aquatic organisms in ballast water discharges; however, these new technologies may not operate as expected at global ports having variable water quality or may periodically malfunction.
Using simulations informed by empirical data, we investigated the risk of non‐indigenous species establishment associated with BWMS inoperability and evaluated potential mitigation strategies. Scenarios considered included bypassed or inoperable BWMS achieving no reduction in organisms, and partially functioning BWMS with discharged organism concentrations exceeding permissible limits. These scenarios were contrasted to outcomes with fully functioning BWMS and to voyages where ballast water exchange (BWE) was used to mitigate risk.
Partially functioning BWMSs were nonetheless beneficial, reducing organism concentrations in ballast and thus establishment risk. When a BWMS is bypassed or partially functioning, BWE is a useful emergency mitigation measure, reducing establishment risks more than partial BMWS. However, the greatest risk reduction was achieved when partial BWMS and BWE were combined.
Voyage‐specific characteristics such as concentration of organisms at uptake and destination port salinity can affect the optimal management strategy for voyages when the BWMS does not achieve compliant discharges.
Synthesis and applications. The risk of aquatic invasions and their associated ecological damages can be substantially reduced by using a ballast water management system (BWMS) and/or ballast water exchange (BWE). When a BWMS is inoperable, appropriate mitigation measures should be decided on a trip‐by‐trip basis considering voyage route and reason for BWMS inoperability (when known). BWE is a useful strategy for reducing invasion risk, except when uptake concentrations are very low. Combining BWE and partial BWMS always reduced risk compared with BWE alone, but did not greatly reduce risk when uptake concentrations were high.
The risk of aquatic invasions and their associated ecological damages can be substantially reduced by using a ballast water management system (BWMS) and/or ballast water exchange (BWE). When a BWMS is inoperable, appropriate mitigation measures should be decided on a trip‐by‐trip basis considering voyage route and reason for BWMS inoperability (when known). BWE is a useful strategy for reducing invasion risk, except when uptake concentrations are very low. Combining BWE and partial BWMS always reduced risk compared with BWE alone, but did not greatly reduce risk when uptake concentrations were high.
Identification of rare species and mapping their distributions is crucial for understanding natural species distributions and causes and consequences of accelerating species declines. However, ...detection of rare species in both terrestrial and especially aquatic communities typically dominated by numerous microscopic species (i.e. rare biosphere) represents a formidable technical challenge. Rapid advances in high-throughput sequencing (HTS) technologies have revolutionized biodiversity studies in the rare biosphere, and also stimulated associated debates. Here we summarize research progress, discuss debates and problems, and propose possible solutions and future studies to address these issues. In addition, we provide take-home messages for experimental design and data interpretation when utilizing HTS techniques for rare biosphere exploration in ecology and conservation biology.
Cyanobacterial blooms, usually dominated by Microcystis aeruginosa, pose a serious threat to global freshwater ecosystems owing to their production and release of various harmful secondary ...metabolites. Detection of the chemicals in M. aeruginosa exudates using metabolomics technology revealed that phytosphingosine (PHS) was one of the most abundant compounds. However, its specific toxicological mechanism remained unclear. CNE-2 cells were selected to illustrate the cytotoxic mechanism of PHS, and it was determined to cause excessive production of reactive oxygen species and subsequently damage the mitochondrial structure. Mitochondrial membrane rupture led to matrix mitochondrial membrane potential disintegration, which induced Ca2+ overload and interrupted ATP synthesis. Furthermore, rupture of the mitochondrial membrane induced the opening of the permeability transition pore, which caused the release of proapoptotic factors into the cytoplasm and the expression of apoptosis-related proteins Bax, Bcl-2, cytochrome-c and cleaved caspase-3 in CNE-2 cells. These events, in turn, activated the mitochondrially mediated intrinsic apoptotic pathway. A mitochondrial repair mechanism, namely, PINK1/Parkin-mediated mitophagy, was then blocked, which further promoted apoptosis. Our findings suggest that more attention should be paid to the ecotoxicity of PHS, which is already listed as a contaminant of emerging concern.
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The number of released individuals, which is a component of propagule pressure, is considered to be a major driver for the establishment success of non-native species. However, propagule pressure is ...often assumed to result from single or few release events, which does not necessarily apply to the frequent releases of invertebrates or other taxa through global transport. For instance, the high intensity of global shipping may result in frequent releases of large numbers of individuals, and the complexity of shipping dynamics impedes predictions of invasion dynamics. Here, we present a mathematical model for the spread of planktonic organisms by global shipping, using the history of movements by 33 566 ships among 1477 ports to simulate population dynamics for the comb jelly Mnemiopsis leidyi as a case study. The degree of propagule pressure at one site resulted from the coincident arrival of individuals from other sites with native or non-native populations. Key to sequential spread in European waters was a readily available source of propagules and a suitable recipient environment. These propagules were derived from previously introduced 'bridgehead' populations supplemented with those from native sources. Invasion success is therefore determined by the complex interaction of global shipping and local population dynamics. The general findings probably hold true for the spread of species in other complex systems, such as insects or plant seeds exchanged via commercial trade or transport.
Zhan et al. (Biological Invasions, 2015, 17:3073–3080) stressed that China’s South-to-North Water Transfer Project (SNWTP)—the world’s largest constructed water diversion—could create an invasion ...highway by facilitating spread of non-native species, including invasive golden mussel
Limnoperna fortunei
. However, most available literature indicated that golden mussels could not survive the cold winter in Northern China. We proposed that phenotypic plasticity and rapid environmental adaptation, combined with relatively high water temperature derived from wastewater treatment plant effluents and a large potential inoculum continuously transported from southern source populations, could jointly contribute to golden mussel spread into northern locations. We conducted surveillance for the species both before and after the waterway was opened in late 2014 in the diversion destination—Beijing. While all surveys in the whole area were negative between 2014 and 2018, we detected rapid geographical expansions in 2019–2021 across multiple waterbodies based on traditional field surveys and environmental DNA (eDNA)-based methods. Surprisingly, we subsequently observed populations that had successfully survived a cold winter in Beijing. The SNWTP may facilitate further spread of cold-adapted populations, placing high-latitude areas at risk. This case study highlights the need for robust scientific assessment and management to predict and mitigate non-native species’ distributional changes that may accompany large-scale hydraulic projects.
Cyanobacterial blooms, often dominated by Microcystis aeruginosa, are capable of producing estrogenic effects. It is important to identify specific estrogenic compounds produced by cyanobacteria, ...though this can prove challenging owing to the complexity of exudate mixtures. In this study, we used untargeted metabolomics to compare components of exudates from microcystin-producing and non-microcystin-producing M. aeruginosa strains that differed with respect to their ability to produce microcystins, and across two growth phases. We identified 416 chemicals and found that the two strains produced similar components, mainly organoheterocyclic compounds (20.2%), organic acids and derivatives (17.3%), phenylpropanoids and polyketides (12.7%), benzenoids (12.0%), lipids and lipid-like molecules (11.5%), and organic oxygen compounds (10.1%). We then predicted estrogenic compounds from this group using random forest machine learning. Six compounds (daidzin, biochanin A, phenylethylamine, rhein, o-Cresol, and arbutin) belonging to phenylpropanoids and polyketides (3), benzenoids (2), and organic oxygen compound (1) were tested and exhibited estrogenic potency based upon the E-screen assay. This study confirmed that both Microcystis strains produce exudates that contain compounds with estrogenic properties, a growing concern in cyanobacteria management.
Dual stresses of cyanobacterial blooms and environmental estrogens in waterbodies are hot topics in environmental science research. Environmental estrogen, an endocrine disrupting chemical, can significantly influence animals or even humans at a low concentration by mimicking endogenous estrogens. Our study demonstrated production and types of estrogenic compounds by M. aeruginosa, and provides specific evidence of cyanobacteria as a potential environmental source of estrogen. This study broadens understanding of cyanobacterial toxins, especially estrogenic compounds.
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•Metabolomic profiles of Microcystis aeruginosa strains do not differ significantly.•We used machine learning to identify estrogenic compounds contained in algae exudates.•Tests using the E-screen assay confirmed estrogenic potency of six exudate compounds.•Estrogenic activity adds to the known adverse effects of M. aeruginosa exudates.
Large-scale high-throughput sequencing techniques are rapidly becoming popular methods to profile complex communities and have generated deep insights into community biodiversity. However, several ...technical problems, especially sequencing artifacts such as nucleotide calling errors, could artificially inflate biodiversity estimates. Sequence filtering for artifact removal is a conventional method for deleting error-prone sequences from high-throughput sequencing data. As rare species represented by low-abundance sequences in datasets may be sensitive to artifact removal process, the influence of artifact removal on rare species recovery has not been well evaluated in natural complex communities. Here we employed both internal (reliable operational taxonomic units selected from communities themselves) and external (indicator species spiked into communities) references to evaluate the influence of artifact removal on rare species recovery using 454 pyrosequencing of complex plankton communities collected from both freshwater and marine habitats. Multiple analyses revealed three clear patterns: 1) rare species were eliminated during sequence filtering process at all tested filtering stringencies, 2) more rare taxa were eliminated as filtering stringencies increased, and 3) elimination of rare species intensified as biomass of a species in a community was reduced. Our results suggest that cautions be applied when processing high-throughput sequencing data, especially for rare taxa detection for conservation of species at risk and for rapid response programs targeting non-indigenous species. Establishment of both internal and external references proposed here provides a practical strategy to evaluate artifact removal process.
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