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The human-mediated introduction of species to regions of the world they could never reach by natural means has had great impacts on the environment, the economy, and society. In the ocean, these invasions have long been mediated by the uptake and subsequent release of ballast water in ocean-going vessels. Increasing world trade and a concomitantly growing global shipping fleet composed of larger and faster vessels, combined with a series of prominent ballast-mediated invasions over the past two decades, have prompted active national and international interest in ballast water management. Assessing the Relationship Between Propagule Pressure and Invasion Risk in Ballast Water informs the regulation of ballast water by helping the Environnmental Protection Agency (EPA) and the U.S. Coast Guard (USCG) better understand the relationship between the concentration of living organisms in ballast water discharges and the probability of nonindigenous organisms successfully establishing populations in U.S. waters. The report evaluates the risk-release relationship in the context of differing environmental and ecological conditions,including estuarine and freshwater systems as well as the waters of the three-mile territorial sea. It recommends how various approaches can be used by regulatory agencies to best inform risk management decisions on the allowable concentrations of living organisms in discharged ballast water in order to safeguard against the establishment of new aquatic nonindigenous species, and to protect and preserve existing indigenous populations of fish, shellfish, and wildlife and other beneficial uses of the nation's waters. Assessing the Relationship Between Propagule Pressure and Invasion Risk in Ballast Water provides valuable information that can be used by federal agencies, such as the EPA, policy makers, environmental scientists, and researchers.

Approximately 65% of established non-indigenous species (NIS) identified in the Great Lakes–Saint Lawrence River basin (GLSLR) since 1959 were introduced by ballast water discharges from transoceanic vessels. While the rate of new detections has sharply declined, NIS already present may spread within the system—including upstream—through secondary invasions by domestic ballast water transferred mainly by ‘laker’ vessels. Canada has mandated that all vessels loading or unloading in waters under Canadian jurisdiction in the GLSLR will need to use ballast water management systems (BWMS) by 2030. Here we used simulations informed by empirical data to investigate the expected efficacy of BWMS in reducing zooplankton and phytoplankton introductions on a per-trip basis, and the corresponding probabilities of survival and establishment related to ballast water discharges within the GLSLR. We investigated three ballast water scenarios: no treatment, full treatment, and treatment by a partially-functioning BWMS (owing to malfunctions or challenging water quality). Fully-functioning BWMS reduced community pressure by > 99% and corresponding establishment risk of NIS by 38% and 66% relative to untreated ballast discharges for zooplankton and phytoplankton, respectively. Partial treatment (modelled as a 95% reduction in organism concentrations) resulted in 10–20% reduction in per-trip probability of NIS establishment; results indicate that trips with BWMS inoperability caused by highly turbid uptake conditions may be less risky than trips with BWMS inoperability due to plankton blooms. The implementation of BWMS is expected to reduce risk of secondary spread within the GLSLR system by ballast water, even if the BWMS are subject to periodic malfunction.

Ships’ ballast water and sediments are vectors that contribute to the unintentional spread of aquatic non-native species globally. Ballast water management, as well as commissioning testing of ballast water management systems and compliance monitoring under the regulations of the International Maritime Organization (IMO) aim at minimizing the unwanted spread of organisms. This study compiles data for treated ballast water samples collected and analyzed from 228 ships during 2017–2023. The samples were collected from the ballast discharge line or directly from the ballast tank for enumeration of living organism concentrations in the categories of ≥50µm and <50 to ≥10µm -sized organisms, as well as indicator microbes in comparison to the ballast water performance standard of the IMO (Regulation D-2). In addition, several ship-specific factors were examined to infer potential factors affecting compliance rates. Nearly all ships were compliant with the ballast water performance standard for indicator microbes and <50 to ≥10µm -sized organisms, whereas almost half of all samples exceeded the limit of ten viable organisms m-3 for the ≥50µm -sized organisms. Compliance testing results did not differ significantly between sampling years, indicating that compliance rate did not change through time. The rate of compliance was higher for commissioning testing than compliance testing. Clear ship- or system-specific factors that lead to compliance or non-compliance were not detected, even though type of ballast water management system, filter mesh size associated with the system and source of ballast water affected compliance significantly either for the samples taken from the discharge line, or ballast tank. As compliance did not improve significantly over time, compliance testing of ships’ ballast water should be undertaken to ensure that the systems remain operational after commissioning and ships meet requirements of the D-2 standard. Furthermore, the study outcomes promote further research on the efficiency of filter mesh sizes and different filtration units associated with ballast water management systems, to improve mechanical removal of larger organisms. Finally, as several ships exceeded the compliance limit by hundreds or thousands of living organisms, technological advancements and operational measures may be needed to improve the overall reliability of ballast water management.

We employed a mesoscale experimental system and enriched natural plankton communities to investigate the efficacy of a type of ballast-water management system (BWMS) that uses a combination of filtration and electro-catalysis as the treatment technology. The water samples were collected immediately after treatment and at discharge to measure the biological efficiency of this BWMS. The main hydro chemical parameters, the TRO concentration and the plankton species composition before and after the ballast treatment process, were measured. After treatment, the concentration of TRO remained at a high level of 1.690 ± 0.573 (SD) mg/L. The biological efficacy of ballast water after treatment at holding times of 10 min, 20 min, 30 min, 40 min, and 50 min were measured. Holding time significantly impacted the biological efficacy. The discharged, treated water satisfied the D-2 standard of the International Maritime Organization (IMO) after 50 minutes of holding time.

Effects of ballast water treatment by advanced electro-catalysis oxidation processes (AEOP) on abundance, activity, and diversity of marine bacteria were examined in a full-scale ballast water management system (BWMS) at Yangshan Port, Shanghai, China. Water samples were collected immediately after treatment and at discharge to evaluate the contingency treatment performance of the BWMS for bacteria. After treatment, the total viable count reduced to 0.7 × 104 CFU·mL−1, and both Escherichia coli and enterococci decreased to 10 CFU·100 mL−1, which satisfied the D-2 Standard of the International Maritime Organization. AEOP can be as an effective contingency reception facility. Sequencing of 16S rRNA gene amplicons demonstrated the declining trend in bacterial diversity, and while the treatment did not completely eliminate the risk of bacterial dispersal, potentially pathogenic bacteria survived in treated and discharged samples. Bacterial diversity is of greater concern when evaluating effects of ballast water treatment on microorganisms because the bacteria which can develop adaptive mechanisms to environmental change will have a greater potential for invasion in the new environment.

The spread of harmful algae through ballast water poses serious threats to marine ecosystems, so the development of effective methods to inactivate the algae and to treat the harmful pollution in ballast water was important. Electrocatalysis technology is safe and reliable and has been widely used in water treatment. In this paper, a dimensionally stable anode (DSA) electrocatalysis system was studied to investigate the efficiency of in-site algae inactivation in simulated ballast water. The studies showed that the DSA electrocatalysis system showed good efficiency for algae inactivation in ballast water, and the inactivation rate varied depending on the algae and could be optimized by adjusting hydraulic retention time (HTR), current density, and electrode surface area. Furthermore, the DSA electrocatalysis provided a significantly sustained inactivation effect on algae in the holding time after electrolytic operation. The inactivation rate for Platymonas helgolandica and Heterosigma akashiwo reached 99.27% and 99.09%, respectively, in short treatment time (HRT of 60 s), and the energy consumption was 0.350 kWh/L and 2.654 kWh/L. Besides the direct oxidation and reduction of electric field, the reactive oxides generated in the DSA electrocatalysis process were the primary factors which caused algae inactivation. The total residual oxides (TRO) damaged algae cells and led to algae inactivation. The DSA electrocatalysis led to lipid peroxidation in algal cell membranes, causing structural damage and metabolic failure. The DSA electrocatalysis was an effective and clean technology for the in-site algae removal in ballast water.

Discharge from the ballast tanks of ships is one of the primary vectors of nonindigenous species in marine environments. To mitigate this environmental and economic threat, international, national, and state entities are establishing regulations to limit the concentration of living organisms that may be discharged from the ballast tanks of ships. The proposed discharge standards have ranged from zero detectable organisms to <10 organisms/m3. If standard sampling methods are used, verifying whether ballast discharge complies with these stringent standards will be challenging due to the inherent stochasticity of sampling. Furthermore, at low concentrations, very large volumes of water must be sampled to find enough organisms to accurately estimate concentration. Despite these challenges, adequate sampling protocols comprise a critical aspect of establishing standards because they help define the actual risk level associated with a standard. A standard that appears very stringent may be effectively lax if it is paired with an inadequate sampling protocol. We describe some of the statistical issues associated with sampling at low concentrations to help regulators understand the uncertainties of sampling as well as to inform the development of sampling protocols that ensure discharge standards are adequately implemented.

Several decades of research on invasive marine species have yielded a broad understanding of the nature of species invasion mechanisms and associated threats globally. However, this is not true of the Arctic, a region where ongoing climatic changes may promote species invasion. Here, we evaluated risks associated with non-indigenous propagule loads discharged with ships' ballast water to the high-Arctic archipelago, Svalbard, as a case study for the wider Arctic. We sampled and identified transferred propagules using traditional and DNA barcoding techniques. We then assessed the suitability of the Svalbard coast for non-indigenous species under contemporary and future climate scenarios using ecophysiological models based on critical temperature and salinity reproductive thresholds. Ships discharging ballast water in Svalbard carried high densities of zooplankton (mean 1522 ± 335 SE individuals m−3), predominately comprised of indigenous species. Ballast water exchange did not prevent non-indigenous species introduction. Non-indigenous coastal species were present in all except one of 16 ballast water samples (mean 144 ± 67 SE individuals m−3), despite five of the eight ships exchanging ballast water en route. Of a total of 73 taxa, 36 species including 23 non-indigenous species were identified. Of those 23, sufficient data permitted evaluation of the current and future colonization potential for eight widely known invaders. With the exception of one of these species, modelled suitability indicated that the coast of Svalbard is unsuitable presently; under the 2100 Representative Concentration Pathway (RCP) 8·5 climate scenario, however, modelled suitability will favour colonization for six species. Synthesis and applications. We show that current ballast water management practices do not prevent non-indigenous species from being transferred to the Arctic. Consequences of these shortcomings will be shipping-route dependent, but will likely magnify over time: our models indicate future conditions will favour the colonization of non-indigenous species Arctic-wide. Invasion threats will be greatest where shipping transfers organisms across biogeographic realms, and for these shipping routes ballast water treatment technologies may be required to prevent impacts. Our results also highlight critical gaps in our understanding of ballast water management efficacy and prioritization. Thereby, our study provides an agenda for research and policy development.

Ballast water has been identified as a leading vector for introduction of non‐indigenous species. Recently, the International Maritime Organization implemented management standards—D‐2—where all large, commercial ships trading internationally are required to adopt an approved treatment system using technologies such as ultraviolet radiation or chlorination. However, current management regulations are based only on the total abundance of viable taxa transported (i.e. total propagule pressure), largely ignoring species richness (i.e. colonization pressure). To determine the efficacy of chlorine treatment in reducing invasion risks and changes in transported biological communities inside ballast tanks, we used DNA metabarcoding‐based approaches to estimate colonization pressure (here, the number of species/operational taxonomic units [OTUs] introduced) and relative propagule pressure (relative abundance of each species/OTU) of zooplankton communities in control and chlorine treated tanks during four transatlantic voyages. Our study demonstrated that transport itself did not significantly reduce colonization pressure of zooplankton species, nor did chlorine treatment. Chlorine treatment altered community structure by reducing relative propagule pressure of some taxa such as Mollusca and Rotifera, while increasing relative propagule pressure of some Oligohymenophorea and Copepoda species. Synthesis and applications. Chlorine treatment may not reduce invasion risks as much as previously thought. Reduction in total propagule pressure does not mean reduction in abundance of all species equally. While some taxa might experience drastically reduced abundance, others might not change at all or increase due to hatching from dormant stages initiated by chlorine exposure. Therefore, management strategies should consider changes in total propagule pressure and colonization pressure when forecasting risk of new invasions. We therefore recommend adopting new approaches, such as DNA metabarcoding‐based methods, to assess the whole biodiversity discharged from ballast water. As species responses to chlorine treatment are variable and affected by concentration, we also recommend a combination of different technologies to reduce introduction risks of aquatic organisms. Foriegn Language 中文摘要 压舱水被认为是全球范围内外来生物传播的重要载体。近期, 《国际船舶压载水及沉积物控制与管理公约》中的D‐2标准正式生效, 这意味着所有进行国际贸易的商业船舶均需要安装基于紫外和氯处理等一系列处理技术的船载压舱水处理系统, 以实现压舱水的达标排放。然而, 现有的管理条例仅仅基于压舱水所传播的存活生物的总丰度（即总繁殖体压力 total propagule pressure）, 而极大忽略了物种丰度（即定植压力 colonization pressure）. 为了评估氯处理技术在减少入侵生物风险中的效率及其对压舱水中浮游动物群落结构及多样性变化的影响, 我们运用DNA宏条形码技术, 比较了四条跨大西洋航线中的空白对照和氯处理压舱水间的浮游动物群落的定植压力【即传播的物种数/操作分类单元（OTUs）数】和相对繁殖体压力（物种/OTUs的相对丰度)。 我们的结果表明, 压舱水传播过程本身（即未经过处理的对照）和氯处理均未能显著减少浮游动物的定植压力。氯处理能有效改变浮游动物群落结构, 一些类群的相对繁殖体压力减少, 例如软体动物和轮虫；而另一些类群的相对繁殖体压力增加, 例如寡膜纲和桡足纲的部分物种。 总结与应用: 氯处理在降低入侵风险方面可能低于预期。总繁殖体压力的降低并不代表所有物种丰度也随之相同程度地降低。一些类群的丰度可能急剧降低, 而另一些类群的丰度则并不改变, 甚至由于氯暴露引发的休眠体孵化而导致部分类群的相对丰度增加。因此, 在预测新的入侵风险时, 管理策略应综合考虑总繁殖体压力和定植压力。因此, 我们也建议采纳新的技术方法来综合评估压舱水中的生物多样性, 例如 DNA 宏条形码技术等。鉴于不同生物对氯处理的响应不同, 我们建议采取多种压舱水处理技术相结合的方法以减少外来水生生物的引入与传播。 Current ballast water management regulations are based only on the total propagule pressure, largely ignoring colonization pressure. While “selection model” (Briski et al., 2018) suggests that reduction in total propagule pressure during transport does not mean reduction in abundance of all species equally, our study demonstrated that chlorine treatment altered community structure by reducing relative propagule pressure of some taxa but increasing relative propagule pressure of other taxa. Therefore, management strategies should consider changes in total propagule pressure and colonization pressure when forecasting risks of new invasions.

Ballast water-mediated bioinvasion is a major threat to the health of aquatic ecosystems. Port environments are hotspots for marine bioinvasion due to ballast water uptake and discharge activities. As the first of its kind pilot study in a tropical ecosystem, we investigated short-term changes in the bacterial community at a port during ballast water discharge (BWD). Total bacterial count and total viable bacteria varied significantly in the port, which can be attributed to BWD. While Vibrio alginolyticus numbers increased, V. parahaemolyticus decreased during BWD, whereas total coliforms were reduced over time. Before BWD, Actinobacteria, β- and γ-proteobacteria were dominant at the port. However, Bacteroidetes and γ-proteobacteria were abundant after BWD, which may have been inoculated in the port through ballast water. Such a shift in bacterial diversity can alter the functional characteristics of the port and is a cause for concern. Investigating the long-term changes due to repeated inoculations will help in developing appropriate environmental management practices.