Abstract
Global coastal aquatic ecosystems are negatively impacted by the introduction of harmful aquatic species through the discharge of ships’ ballast water. To reduce discharges of harmful aquatic organisms and pathogens, such as toxic phytoplankton species, ships are now transitioning to the use of ballast water management systems (BWMS) instead of ballast water exchange (BWE). This study examines the abundance and diversity of phytoplankton in ballast water managed by BWMS (or a combination of both BWE + BWMS) in comparison to those in ballast water managed by BWE alone (collected from ships arriving to Canada’s Pacific coast in 2017–2018 and 2008, respectively). The abundance and diversity of phytoplankton species were also examined in relation to key variables such as ballast water salinity and ballast water age. Total abundance of phytoplankton was significantly lower in preserved samples managed by either a BWMS or BWE + BWMS compared to BWE alone. Abundances in preserved samples were higher than observed in fresh (unpreserved) samples at the time of collection, with all samples managed by a BWMS meeting international limits for the number of viable organisms ≥10 and <50 μm in minimum dimension (based on six 1-mL live counts). While there was no apparent influence of factors such as treatment type [e.g., ultraviolet (UV) or chlorine], presence of filtration, ballast water salinity, ballast water age, nor location of last ballast water uptake on phytoplankton abundances in preserved samples, power to detect differences may be limited by sample size. Ballast water managed by BWMS also tended to have lower abundances of harmful phytoplankton species, although the difference was not statistically significant – additional research into the community composition of live cells in fresh samples could be valuable to discriminate the risk associated with phytoplankton surviving ballast water treatment.
Highlights
To serve the demand of globalization, trade by ships has increased steadily in recent decades and will continue to do so, with the number, sizes, and speed of ships increasing (Calatayud et al, 2017; Carney et al, 2017)
The generalized linear model (GLM) analyses run as a function of ballast water salinity or ballast water age showed that the total abundance of phytoplankton was significantly different in samples from ships performing ballast water exchange (BWE) than those using ballast water management systems (BWMS) only (Z-value = −2.79; P-value < 0.001) and BWE + BWMS (Z-value = −2.81; P-value < 0.001)
Samples managed by a BWMS having a filtration step tended to have higher total abundances of phytoplankton in preserved ballast water samples than those without a filtration step, though this is confounded by individual ballast histories
Summary
To serve the demand of globalization, trade by ships has increased steadily in recent decades and will continue to do so, with the number, sizes, and speed of ships increasing (Calatayud et al, 2017; Carney et al, 2017). Using BWMS to Prevent Harmful Algae around the world, including associated living organisms, are frequently discharged far from the source ecosystem. Casas-Monroy et al (2015) estimated that more than 116 million tonnes of ballast water (and associated living organisms) are discharged in Canadian coastal port environments annually. Several phytoplankton species are harmful or toxic, and have been associated with ship-mediated introductions in different countries [e.g., Australia: Hallegraeff and Bolch (1992); Great Britain: Hamer et al (2001)], sometimes with dramatic ecological and economic consequences, for aquaculture farmers (Trottet et al, 2021). The transport and introduction of non-indigenous species and harmful species of phytoplankton by ballast water is a pressing environmental problem worldwide (Bailey, 2015; Casas-Monroy et al, 2015; Bailey et al, 2020)
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