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.
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.
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.
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.
Aim: Introduced alien species are frequently implicated in ecosystem disruption and biodiversity loss, but some ecologists have recently argued that efforts to manage ecosystems should be refocused ...on known problematic species without regard to whether such species are native or alien. This argument rests on the premise that native and alien species in general do not differ in their impacts. Although there are numerous cases that suggest alien predators and herbivores can sometimes cause severe declines or even local extinctions of native species, very few studies have compared the impacts of native and alien consumers on native populations. Location: World-wide. Methods: We have conducted a meta-analysis on a global dataset to compare the effects of native and alien predators and herbivores on native populations occupying a broad range of terrestrial and aquatic environments. Results: The distribution of positive, negative and neutral effects on native prey abundance differed significantly by consumer origin, with alien consumers associated with more negative and fewer positive effects than expected, opposite the finding for native consumers. The effect size of alien consumers was 2.4 times greater than that of native consumers and did not differ between predators and herbivores. The impact of alien consumers did not differ significantly in aquatic (lakes, rivers, oceans) versus terrestrial (continental, island) habitats. Similarly, there was no significant interaction between consumer origin and location, as consumers had similar effects in insular (freshwater, island) and open (continental, marine) systems — contrary to the notion that alien species impacts are mainly problematic for island biota. Main conclusions: We hypothesize that the ecological naïveté of native biota facilitates their enhanced suppression by alien predators and herbivores relative to native enemies. Our results counter the assertion that the biogeographical origin of species has no bearing on their ecological impact.
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.
Determining the degree of population connectivity and investigating factors driving genetic exchange at various geographical scales are essential to understanding population dynamics and spread ...potential of invasive species. Here, we explore these issues in the highly invasive vase tunicate, Ciona intestinalis, a species whose invasion history has been obscured by its poorly understood taxonomy and population genetics. Recent phylogenetic and comparative genomic studies suggest that C. intestinalis is a cryptic species complex consisting of at least three species. We reconstructed phylogenies based on both mitochondrial (cytochrome c oxidase subunit 3—NADH dehydrogenase subunit 1 region and NADH dehydrogenase subunit 4 gene) and nuclear (internal transcribed spacer 1) sequences, results of which support four major phylogroups corresponding to the previously reported spA, spB and Ciona spp. (spC) as well as an undescribed cryptic species (spD). While spC and spD remain restricted to their native ranges in the Mediterranean Sea and Black Sea, respectively, the highly invasive species (spA and spB) have disjunct global distributions. Despite extensive interspecific divergences, we identified low phylogeographical structure within these two invasive species. Haplotype network analyses revealed comparatively limited mutation steps among haplotypes within each species. Population genetic analyses based on two mtDNA fragments and eight unlinked microsatellites illustrated relatively low population differentiation and high population connectivity at both regional and continental scales in the two invasive species. Human‐mediated dispersal coupled with a high potential for natural dispersal is probably responsible for the observed genetic homogeneity.
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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AIM: The urgent need for large‐scale spatio‐temporal assessments of biodiversity in the face of rapid environmental change prompts technological advancements in species identification and ...biomonitoring such as metabarcoding. The high‐throughput DNA sequencing of bulk samples offers many advantages over traditional morphological identification for describing community composition. Our objective was to evaluate the applicability of metabarcoding to identify species in taxonomically complex samples, evaluate biodiversity trends across broad geographical and temporal scales and facilitate cross‐study comparisons. LOCATION: Marine and freshwater ports along Canadian coastlines (Pacific, Arctic and Atlantic) and the Great Lakes. METHODS: We used metabarcoding of bulk zooplankton samples to identify species and profile biodiversity across habitats and seasons in busy commercial ports. A taxonomic assignment approach circumventing sequence clustering was implemented to provide increased resolution and accuracy compared to pre‐clustering. RESULTS: Taxonomic classification of over seven million sequences identified organisms spanning around 400 metazoan families and complements previous surveys based on morphological identification. Metabarcoding revealed over 30 orders that were previously not reported, while certain taxonomic groups were underrepresented because of depauperate reference databases. Despite the limitations of assigning metabarcoding data to the species level, zooplankton communities were distinct among coastlines and significantly divergent among marine, freshwater and estuarine habitats even at the family level. Furthermore, biodiversity varied substantially across two seasons reaching a beta diversity of 0.9 in a sub‐Arctic port exposed to high vessel traffic. MAIN CONCLUSIONS: Metabarcoding offers a powerful and sensitive approach to conduct large‐scale biodiversity surveys and allows comparability across studies when rooted in taxonomy. We highlight ways of overcoming current limitations of metabarcoding for identifying species and assessing biodiversity, which has important implications for detecting organisms at low abundance such as endangered species and early invaders. Our study conveys pertinent and timely considerations for future large‐scale monitoring surveys in relationship to environmental change.
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.
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