Relative invasion risk for plankton across marine and freshwater systems: examining efficacy of proposed international ballast water discharge standards

The global social-economic dimension of biological invasions by plankton: Grossly underestimated costs but a rising concern for water quality benefits?

Planktonic invasive species cause adverse effects on aquatic biodiversity and ecosystem services. However, these impacts are often underestimated because of unresolved taxonomic issues and limited biogeographic knowledge. Thus, it is pivotal to start a rigorous quantification of impacts undertaken by planktonic invasive species on global economies. We used the InvaCost database, the most up-to-date database of economic cost estimates of biological invasions worldwide, to produce the first critical assessment of the economic dimension of biological invasions caused by planktonic taxa. We found that in period spanning from 1960 to 2021, the cumulative global cost of plankton invasions was US$ 5.8 billion for permanent plankton (holoplankton) of which viruses encompassed nearly 93%. Apart from viruses, we found more costs related to zooplankton (US$ 297 million) than to the other groups summed, including myco- (US$ 73 million), phyto- (43 million), and bacterioplankton (US$ 0.7 million). Strikingly, harmful and potentially toxic cyanobacteria and dinoflagellates are completely absent from the database. Furthermore, the data base showed a decrease in costs over time, which is probably an artifact as a sharp rise of novel planktonic alien species has gained international attention. Also, assessments of the costs of larval meroplanktonic stages of littoral and benthic invasive invertebrates are lacking whereas cumulative global cost of their adults stages is high up to US$ 98 billion billion and increasing. Considering the challenges and perspectives of increasing but unnoticed or neglected impacts by plankton invasions, the assessment of their ecological and economic impacts should be of high priority.

Prediction of Alexandrium and Dinophysis algal blooms and shellfish contamination in French Mediterranean Lagoons using decision trees and linear regression: a result of 10 years of sanitary monitoring

French Mediterranean lagoons are frequently subject to shellfish contamination by Diarrheic Shellfish Toxins (DSTs) and Paralytic Shellfish Toxins (PSTs). To predict the effect of various environmental factors (temperature, salinity and turbidity) on the abundance of the major toxins producing genera, Dinophysis and Alexandrium, and the link with shellfish contamination, we analysed a 10-year dataset collected from 2010 to 2019 in two major shellfish farming lagoons, Thau and Leucate, using two methods: decision trees and Zero Inflated Negative Binomial (ZINB) linear regression models. Analysis of these decision trees revealed that the highest risk of Dinophysis bloom events occurred at temperature <16.3°C and salinity <27.8, and of Alexandrium at temperature ranging from 10.4 to 21.5°C and salinity >39.2. The highest risk of shellfish contaminations by DSTs and PSTs occurred during the set of conditions associated with high risk of bloom events. Linear regression prediction enables us to understand whether temperature and salinity influence the presence of Alexandrium and affect its abundance. However, Dinophysis linear regression could not be validated due to overdispersion issues. This work demonstrates the tools which could help sanitary management of shellfish rearing areas.

Risk assessment of marine invasive species in Chinese ports introduced by the global shipping network

The discharge of ballast water from ocean-going ships is a major pathway by which invasive species are introduced into coastal waters. As a global factory and trade power with extensive shipping networks, China has paid a huge ecological price for its progress. However, current endeavors to protect the nation's biodiversity are largely focused on terrestrial ecosystems. Therefore, for the first time, we conducted a comprehensive risk assessment of ballast water-induced biological invasion in Chinese ports. The results showed that the ports in the Yangtze River Delta, Pearl River Delta, and Southern Taiwan Province face significantly high invasion risks, and the number of donor ports, connected ships, and arriving vessels showed a positive correlation with the invasion risk. Further, we observed that even a low efficacy disinfection of ballast water can still significantly decrease the level of invasion risk.

Plankton classification with high-throughput submersible holographic microscopy and transfer learning

BACKGROUND

Plankton are foundational to marine food webs and an important feature for characterizing ocean health. Recent developments in quantitative imaging devices provide in-flow high-throughput sampling from bulk volumes-opening new ecological challenges exploring microbial eukaryotic variation and diversity, alongside technical hurdles to automate classification from large datasets. However, a limited number of deployable imaging instruments have been coupled with the most prominent classification algorithms-effectively limiting the extraction of curated observations from field deployments. Holography offers relatively simple coherent microscopy designs with non-intrusive 3-D image information, and rapid frame rates that support data-driven plankton imaging tasks. Classification benchmarks across different domains have been set with transfer learning approaches, focused on repurposing pre-trained, state-of-the-art deep learning models as classifiers to learn new image features without protracted model training times. Combining the data production of holography, digital image processing, and computer vision could improve in-situ monitoring of plankton communities and contribute to sampling the diversity of microbial eukaryotes.

RESULTS

Here we use a light and portable digital in-line holographic microscope (The HoloSea) with maximum optical resolution of 1.5 μm, intensity-based object detection through a volume, and four different pre-trained convolutional neural networks to classify > 3800 micro-mesoplankton (> 20 μm) images across 19 classes. The maximum classifier performance was quickly achieved for each convolutional neural network during training and reached F1-scores > 89%. Taking classification further, we show that off-the-shelf classifiers perform strongly across every decision threshold for ranking a majority of the plankton classes.

CONCLUSION

These results show compelling baselines for classifying holographic plankton images, both rare and plentiful, including several dinoflagellate and diatom groups. These results also support a broader potential for deployable holographic microscopes to sample diverse microbial eukaryotic communities, and its use for high-throughput plankton monitoring.

Abiotic and biological differences in ballast water uptake and discharge samples

During the type approval process of ballast water management systems (BWMS) performance tests need to be conducted according to the BWMS Code (previously Guidelines G8) of the International Maritime Organization (IMO). The shipboard tests previously included a control experiment with untreated ballast water to evaluate the BWMS performance by comparing test results of treated and untreated water. Biological results and abiotic parameters of 97 control water tests conducted during the last >10 years during ballast water uptakes and corresponding discharges were summarized. In general, a strong decline of organisms in ballast tanks was observed, especially during the first few days of the holding time. The IMO validity criteria for uptake water phytoplankton in shipboard control tests were met in 82.5% of all tests. Phytoplankton numbers below the validity criteria occurred predominantly in winter and/or when the water was taken up offshore. For zooplankton the validity criteria were always met. The TSS and POC content in our ballast water uptake samples was frequently much higher than required during IMO BWMS type approval tests so that the current testing requirements do not represent a challenge to BWMS. With this a risk is taken that type approved BWMS fail in water conditions which occur frequently in the real world.

Ballast Water Exchange Plus Treatment Lowers Species Invasion Rate in Freshwater Ecosystems

The movement of ballast water by commercial shipping is a prominent pathway for aquatic invasions. Ships' ballast water management is now transitioning from open ocean exchange to a ballast water performance standard that will effectively require use of onboard treatment systems. Neither strategy is perfect, therefore, combined use of ballast water exchange plus treatment has been suggested to provide greatest protection of aquatic ecosystems. This study compared the performance of exchange plus treatment against treatment alone by modeling establishment rates of nonindigenous zooplankton introduced by ballast water across different habitat types (fresh, brackish, and marine) in Canada. Treatment was modeled under two efficacy scenarios (100% and 50% of ship trips) to consider the possibility that treatment may not always be successful. The model results indicate that exchange plus treatment will be more effective than treatment alone at reducing establishments when recipient ports are freshwater (58 140 vs 11 338 trips until ≥1 establishment occurs, respectively). Exchange plus treatment also serves as an important backup strategy if treatment systems are partially effective (50% of trips), primarily for freshwater recipient ecosystems (1442 versus 585 trips until ≥1 establishment occurs, respectively).

Shifting trophic control of fishery-ecosystem dynamics following biological invasions

Increasing human population size and mobility have accelerated the translocation of nonnative species globally, which has become a major threat to conservation of biodiversity and ecosystem services. Introduced species can disrupt species interactions of the recipient ecosystem, triggering system-wide events, and amplify or dampen effects of existing pressures. We show how two pervasive intercontinental invasive consumers in North American lakes, dreissenids (filter-feeding mussels) and Bythotrephes (carnivorous zooplankton), nonlinearly modify consumer-resource dynamics and undermine management interventions to rebuild cold-water predatory fish biomass. Synthesizing 30 yr (1986-2015) of lake-wide monitoring data with a dynamic mass-balance food-web model (consisting of 61 species and trophic groups), we reconstructed historical food-web dynamics of Lake Simcoe, a large, temperate lake in Ontario, Canada that has shifted from a turbid to clear-water state. We then analyzed patterns of biomass fluctuations of three recreationally harvested, ecologically connected populations; lake trout (Salvelinus namaycush, a piscivore), lake whitefish (Coregonus clupeaformis, a benthivore), and cisco (C. artedi, a planktivore) before and after the invasions by testing hypotheses on their delayed recoveries under management interventions-predator manipulations (fishery removal and stocking) and nutrient (phosphorus) load reduction. Analyses suggest that fishery harvest primarily regulated early recovery trajectories of the piscivore and planktivore, weakening top-down control prior to the establishment of the invasive consumers. By contrast, the benthivore biomass patterns were shaped, in part, by the invasive mussels (via diet shift), independently of management actions. Although improved water quality (with reduced hypoxia in deeper water) and, in turn, higher macrophyte production are projected to expand the predation refuge for young fish, intensified planktivory (by Bythotrephes) and herbivory (by dreissenids) have triggered shifts in community composition (from pelagic to demersal dominance). These system-wide shifts, in turn, have substantially diminished ecosystem productivity, thereby shrinking fishery yields. Novel consumers can rewire food webs, disrupt energy flows, and suppress predator recoveries, underscoring the need to account for altered ecological reality when sustainably managing fishery resources in invaded ecosystems.

Trends in the detection of aquatic non-indigenous species across global marine, estuarine and freshwater ecosystems: A 50-year perspective

Aim:

The introduction of aquatic non-indigenous species (ANS) has become a major driver for global changes in species biogeography. We examined spatial patterns and temporal trends of ANS detections since 1965 to inform conservation policy and management.

Location:

Global.

Methods:

We assembled an extensive dataset of first records of detection of ANS (1965–2015) across 49 aquatic ecosystems, including the (a) year of first collection, (b) population status and (c) potential pathway(s) of introduction. Data were analysed at global and regional levels to assess patterns of detection rate, richness and transport pathways.

Results:

An annual mean of 43 (±16 SD) primary detections of ANS occurred–one new detection every 8.4 days for 50 years. The global rate of detections was relatively stable during 1965–1995, but increased rapidly after this time, peaking at roughly 66 primary detections per year during 2005–2010 and then declining marginally. Detection rates were variable within and across regions through time. Arthropods, molluscs and fishes were the most frequently reported ANS. Most ANS were likely introduced as stowaways in ships’ ballast water or biofouling, although direct evidence is typically absent.

Main conclusions:

This synthesis highlights the magnitude of recent ANS detections, yet almost certainly represents an underestimate as many ANS go unreported due to limited search effort and diminishing taxonomic expertise. Temporal rates of detection are also confounded by reporting lags, likely contributing to the lower detection rate observed in recent years. There is a critical need to implement standardized, repeated methods across regions and taxa to improve the quality of global-scale comparisons and sustain core measures over longer time-scales. It will be fundamental to fill in knowledge gaps given that invasion data representing broad regions of the world's oceans are not yet readily available and to maintain knowledge pipelines for adaptive management.

Nuisance Algae in Ballast Water Facing International Conventions. Insights from DNA Metabarcoding in Ships Arriving in Bay of Biscay

Ballast water is one of the main vectors of transport of nuisance species among marine ports. Neither treatment nor interchange completely reduces the risk of ballast water containing DNA from harmful species, being a signal of potential threat. However, although there are some efficient treatments, they are not available on all ships and there might be some technological/economical constrains for their active and routine usage. Understanding what routes lead to a higher risk of contamination is important for designing targeted surveillance. We analysed ballast water from seven ships arriving in Gijon port (south Bay of Biscay, Spain). DNA metabarcoding was employed for identification of exotic species and harmful algae. One ship carried DNA of 20 risk species in the ballast water. Three ships contained DNA of only one risk species, and three ships had none. Seventy two algae species were found, 22.2% are exotic to the Bay of Biscay and 11.1% are catalogued as harmful. The results demonstrated the importance of continuous surveillance of ballast water.

Are workers on board vessels involved with chemicals from treated ballast water sufficiently protected? - A decadal perspective and risk assessment

Ballast Water Managements Systems (BWMS) installed on vessels may use Active Substances (AS) to inactivate organisms. This paper provides new insights in the global issue of noxious Disinfection By-Products (DBP) produced with primarily oxidant-based BWMS, and the risk assessment for workers, including port State control officers, while performing tasks on a vessel that involve exposure to treated ballast water. The Joint Group of Experts on the Scientific Aspects of Marine Environmental Protection - Ballast Water Working Group (GESAMP-BWWG) plays a role in the certification process of BWMS that make use of AS evaluating potential negative effects. All BWMS that passed GESAMP-BWWG Final Approval until mid 2019 were analyzed providing an overview of chemicals in the treated ballast water before and after neutralization. The ballast tank cleaning scenario, the sampling scenario, and the ballast tank inspection scenario all showed elevated human health risks using the Derived Minimal Effect Levels approach. The most critical exposure occurs in the ballast tank cleaning scenario through the inhalation of volatile DBP, such as tribromomethane. This substance may cause acute effects such as headache, dizziness and also has carcinogenic properties. The two risk reducing options available in the GESAMP-BWWG Tier 2 calculations were compared, one being mitigation measures such as protective gloves and coveralls, the other option is taking into account a time correction factor. The results showed that the trihalomethanes in air are most problematic, however, there is a possibility that the calculated values may be overestimated as generally worst case assumptions were used.

Is human health sufficiently protected from chemicals discharged with treated ballast water from vessels worldwide? - A decadal perspective and risk assessment

Ballast water managements systems (BWMS) installed on vessels may use active substances to inactivate organisms. This paper provides new insights in the global issue of noxious disinfection by-products (DBP) discharge with ballast water, and the related risk assessment for human health. The GESAMP ballast water working group plays a role in the certification process of BWMS that make use of active substances evaluating potential negative effects. We analyzed all BWMS that passed GESAMP final approval over a decade until 2017 providing an overview of chemicals in the discharged ballast water generated by BWMS. We used these data to calculate the chemical load humans may be exposed to for two different commercial ports (Koper, Slovenia and Hamburg, Germany). None of the chemicals in this study reached levels of concern that would indicate a risk for humans after exposure to chemicals present in the discharged ballast water. Nevertheless, although this exposure only adds to a lesser degree to the overall exposure to disinfection by-products, some chemicals, such as tribromomethane, have carcinogenic properties. In case studies we show which chemicals have the largest contribution to the aggregated exposure of humans. We note that tribromomethane, despite its low bio-concentration factor (BCF), may accumulate in fat, when fish are continuously exposed to DBPs during low-level chlorination. Since this figure would give a higher value for the internal dose for tribromomethane from seafood consumption than the current BCF in the GISIS database, the calculated value may underestimate the contribution of tribromomethane, and possibly also other DBPs.

Ecological risk assessment of predicted marine invasions in the Canadian Arctic

Climate change is impacting environmental conditions, especially with respect to temperature and ice cover in high latitude regions. Predictive models and risk assessment are key tools for understanding potential changes associated with such impacts on coastal regions. In this study relative ecological risk assessment was done for future potential introductions of three species in the Canadian Arctic: periwinkle Littorina littorea, soft shell clam Mya arenaria and red king crab Paralithodes camtschaticus. These species occur in locations connected to Canadian Arctic ports through shipping and have the potential to be introduced via ballast water discharge. The methodology proposed in this study is unique in the sense that it considers not only ballast water origin, but also the distribution of the species being assessed and the sensitivity of the receiving habitat. It combines detailed information (ballast water source of each tank, transit time, time of the year when the water is released, environmental suitability of receiving habitat, impact, and habitat sensitivity) in order to assess ecological risk. Through the use of this approach it is highlighted that domestic discharge events pose a higher relative overall risk on a vessel-specific and cumulative annual bases than international discharges. The main ports of Deception Bay and Churchill were classified as being at moderate to high relative risk for L. littorea and M. arenaria, especially from domestic vessels, while relative overall risk for P. camtschaticus was low for international vessels and null for domestic vessels due to few ships transiting from its range of distribution to Canadian Arctic ports. This work can serve as an approach to help build a list of potential high risk species–a “grey” watch list–for the Canadian Arctic, and provides useful information for consideration in future decision making actions such as the identification of high risk pathways, species and ports.

Where else? Assessing zones of alternate ballast water exchange in the Canadian eastern Arctic

Mid-ocean ballast water exchange (BWE) is recommended for international vessels to minimize the transfer of nonindigenous species (NIS). When this cannot be accomplished due to safety concerns, alternate ballast water exchange zones (ABWEZ) may be used. A coupled-ice-ocean model with meteorological forcing and particle tracking was used to evaluate the relative risks from BWE along primary shipping routes into Canada's eastern Arctic. Relative risk to receiving habitats from BWE was calculated from the product of likelihood of exposure, likelihood of establishment, and habitat sensitivity to potential NIS. Modelling results indicate that existing ABWEZs in and around Lancaster Sound and Hudson Strait are among the areas of highest relative risk for introductions of NIS via ballast water. The deeper offshore regions of Labrador Sea and Baffin Bay should be considered as alternatives. However, further research is recommended to assess the risks of NIS associated with BWE in the Canadian Arctic.

Is the aquatic environment sufficiently protected from chemicals discharged with treated ballast water from vessels worldwide? - A decadal environmental perspective and risk assessment

Ballast water managements systems (BWMS) installed on vessels may use active substances to inactivate or kill organisms in the ballast water. This paper provides new insights in this global issue - discharge of hazardous disinfection by-products with ballast water and related risk assessment for the environment. Considering the possible extent of this issue, the International Maritime Organization (IMO) engaged the Joint Group of Experts on the Scientific Aspects of Marine Environmental Protection (GESAMP)-Ballast Water Working Group (BWWG) to oversee the evaluation process of BWMS that make use of active substances to prevent negative effects. We analysed all BWMS that received IMO final approval over a decade until 2017 and provide an overview of active substances used for ballast water treatment and disinfection by-products in the discharged ballast water. A risk assessment was conducted using the GESAMP-BWWG methodology for two very different commercial ports (Koper, Slovenia and Hamburg, Germany). Some relevant chemicals (chloropicrin, monochloroacetic acid, and dibromoacetonitrile) and other chemicals (isocyanuric acid and sodium thiosulphate) reached levels of concern, indicating a risk for aquatic organisms after discharge of that ballast water. From this analysis, it became clear GESAMP-BWWG worst-case scenario assumptions do not fully account for the potential environmental risks. We provide recommendations how to make this risk assessment more robust, recommend further research, and urge for policy as well as regulatory responses.