Integrated Biological Risk and Cost Model Analysis Supports a Geopolitical Shift in Ballast Water Management

Abstract

This work evaluates efficacies of plausible ballast water management strategies and standards by integrating a global species spread risk assessment with a policy cost-effectiveness analysis. Specifically, we consider species spread risks and costs of port-and vessel-based strategies under both current organism concentration standards and stricter standards proposed by California. For each scenario, we estimate species spread risks and patterns using a higher-order analysis of a global ship-borne species spread model and estimate fleet costs for vessel-and barge-based ballast water treatment systems for each standard. We find that stricter standards may reduce species spread risk by a factor of 17 globally and would greatly simplify the complex network of shipborne species spread. The current policy of IMO standards is most cost-effectively achieved through ship-based treatment, and that any additional risk reduction will be most cost-effectively achieved by port-based (or barge-based) technologies, particularly if these are strategically implemented at the top ports within the largest clusters. Bargebased ballast water management would require a shift in governance, and we suggest that this next level of policymaking could be feasible for special areas designated by the IMO, by State or multistate authorities, or by voluntary port applications.

Global Impacts of a Bilateral Trade Policy on Ballast Water-Mediated Species Spread Risk: A Case Study of Sino-US Trade

“…It should be noted that the Species Flow Higher-Order-Network used in this work is based on several assumptions, as stated in the paper cited . The NIS spread risk assessment results obtained with the model are relative risks, which cannot be used to measure the absolute NIS spread risk to a region.…”

“…p (nonindigenous) ij is 0 if the two origin and destination ports of the ship movement are in the same or neighboring ecoregions, and it is 1 if not. This is based on the same assumption in previous studies ,, because the species in the same or neighboring ecosystems tend to be similar because of the natural dispersal , and the invasion risk quantified here is by ballast water discharge instead of natural dispersal.…”

“…It should be noted that the Species Flow Higher-Order-Network used in this work is based on several assumptions, as stated in the paper cited. 30 The NIS spread risk assessment results obtained with the model are relative risks, which cannot be used to measure the absolute NIS spread risk to a region. In addition, the model does not take into account the phenomenon of secondary spread, or the potential harm of invasions as explained in our past work.…”

“…In addition, the model does not take into account the phenomenon of secondary spread, or the potential harm of invasions as explained in our past work. 30 The SF-HON model in this work is only focused on ballast water-mediated species spread, and it does not include other important vectors, such as biofouling or aquaculture. We admit the limitations of using the ballast water discharge records of National Ballast Information Clearinghouse to estimate the discharge profile for the worldwide ports, since the discharge profiles for other regions might be different from the US ports.…”

Transmission of stony coral tissue loss disease (SCTLD) in simulated ballast water confirms the potential for ship-born spread

“…Additional treatments found commonly in BWMS such as filtration, chlorination, and ozonation (reviewed in 38 ), are likely to be more effective means of reducing the risk of SCTLD spread through ships' ballast water as they have shown to have strong biocidal properties 48 , with a lower potential of bacterial regrowth 49,50 or UV resistance [51][52][53] as has been reported with UV treatment alone. There are, however, logistical and cost limitations associated with the implementation and maintenance of more sophisticated BWMS on ships, including considerations for additional fuel usage and cost-benefit biological risk assessments associated with discharge impacts with untreated versus treated ballast water [54][55][56][57] . Further, chemical treatments require www.nature.com/scientificreports/ neutralization and/or removal of byproducts prior to release 38,58,59 , posing potential challenges for ship-based ballast management, as well as evaluation of treatment effectiveness against SCTLD in lab-scale experimental approaches.…”