Lisa A. Drake

Global spread of microorganisms by ships

Commercial ships have spread many species around the world, but little is known of the extent and potential significance of ship-mediated transfer of microorganisms. Here we show that the global movement of ballast water by ships creates a long-distance dispersal mechanism for human pathogens and may be important in the worldwide distribution of microorganisms, as well as for the epidemiology of waterborne diseases affecting plants and animals.

Potential invasion of microorganisms and pathogens via ‘interior hull fouling’: biofilms inside ballast water tanks

Surfaces submerged in an aquatic milieu are covered to some degree with biofilms – organic matrices that can contain bacteria, microalgae, and protozoans, sometimes including disease-causing forms. One unquantified risk of aquatic biological invasions is the potential for biofilms within ships’ ballast water tanks to harbor pathogens, and, in turn, seed other waters. To begin to evaluate this vector, we collected biofilm samples from tanks’ surfaces and deployed controlled-surface sampling units within tanks. We then measured a variety of microbial metrics within the biofilms to test the hypotheses that pathogens are present in biofilms and that biofilms have higher microbial densities compared to ballast water. Field experiments and sampling of coastwise and oceangoing ships arriving at ports in Chesapeake Bay and the North American Great Lakes showed the presence of abundant microorganisms, including pathogens, in biofilms. These results suggest that ballast-tank biofilms represent an additional risk of microbial invasion, provided they release cells into the water or they are sloughed off during normal ballasting operations.

Stratification of living organisms in ballast tanks: how do organism concentrations vary as ballast water is discharged?

Vertical migrations of living organisms and settling of particle-attached organisms lead to uneven distributions of biota at different depths in the water column. In ballast tanks, heterogeneity could lead to different population estimates depending on the portion of the discharge sampled. For example, concentrations of organisms exceeding a discharge standard may not be detected if sampling occurs during periods of the discharge when concentrations are low. To determine the degree of stratification, water from ballast tanks was sampled at two experimental facilities as the tanks were drained after water was held for 1 or 5 days. Living organisms ≥50 μm were counted in discrete segments of the drain (e.g., the first 20 min of the drain operation, the second 20 min interval, etc.), thus representing different strata in the tank. In 1 and 5 day trials at both facilities, concentrations of organisms varied among drain segments, and the patterns of stratification varied among replicate trials. From numerical simulations, the optimal sampling strategy for stratified tanks is to collect multiple time-integrated samples spaced relatively evenly throughout the discharge event.

Review of “Global maritime transport and ballast water management” by M. David and S. Gollasch, eds.

Given the volume of ballast water transported annually in the global fleet (billions of tonnes, depending on the reference) and the notable ecological and economic effects engendered by some introduced species (e.g., Dressenia polymorpha and Mnemiopsis leidyi), international, national, and state policies have been promulgated. They intend to decrease the transport and delivery of introduced species. Most notably, limits on the discharge of living organisms in ballast water are being enacted by the United Nation’s maritime body, the International Maritime Organization (IMO), and they are reflected in legislation at smaller scales, at the national level (e.g., as promulgated in the US, Australia, and New Zealand), the regional level (e.g., the Regional Organization for the Protection of the Marine Environment [ROPME] in the Persian Gulf and Oman Sea), and the state level (e.g., California). In response to the limits on an estimated 60,000 commercial vessels affected by the discharge standard, a ballast water treatment industry has developed. The approaches tend to be borrowed from existing wastewater treatment, although shipboard treatment is greatly complicated by the difficulties of working in a shipboard environment coupled with space and time restrictions. The industry’s value—once uncertainty with respect to regulations and testing is removed—is projected to be a staggering

Validation trials of a shipboard filter skid (p3SFS) demonstrate its utility for collecting living zooplankton.

30–50 billion USD (Ballast Water Management Summit 2015). This book characterizes the complex—and rapidly changing—array of maritime policies and proposed solutions that has grown up around the issue of introduced species in ballast water. Based on their work in the field of ballast water research and management, the editors of Global Maritime Transport and Ballast Water Management compile a series of papers intended to serve students and scientists in aquatic ecology and maritime-related fields of study (marine transport, naval architecture, and policy making). The book provides a detailed review of the state of ballast water management, with a structure that enables readers to build a comprehensive understanding of the technical, policy, and ecological issues. Following an introductory chapter that includes an overview of how vessels use and discharge ballast water, the discussion shifts to the problems caused by biological invasions of non-native species transported in ballast water. The next two chapters describe the policy and legal framework of the Ballast Water Management Convention adopted by the IMO. In subsequent chapters, currently available ballast water management systems (BWMS) are reviewed, ballast water management and risk assessment (RA) are discussed, and sampling and analytical methods are described. Two chapters devoted to the authors’ L. A. Drake (&) Chemistry Division, Naval Research Laboratory, Code 6136, Key West, FL 33041, USA e-mail: lisa.drake@nrl.navy.mil

3D imaging provides a high-resolution, volumetric approach for analyzing biofouling

Relatively large volumes of water-on the order of cubic meters-must be sampled and analyzed to generate statistically valid estimates of sparsely concentrated organisms, such as in treated ballast water. To this end, a third prototype of a shipboard filter skid (p3SFS) was designed and constructed. It consisted of two housings (each containing a 35 μm mesh filter bag) and its own pump and computer controller. Additionally, the skid had a drip sampler, which collected a small volume (∼ 10 L) of whole (unfiltered) water immediately upstream of the housings. Validation of the p3SFS occurred in two segments: (1) land-based trials, in which the collection of organisms ⩾ 50 μm (nominally zooplankton) by the p3SFS was compared to a plankton net, and (2) shipboard trials, in which ballast water was sampled aboard a ship. In both types of trials, the data collected showed the filter skid to be an appropriate flow-through sampling device.

Potential microbial bioinvasions via ships' ballast water, sediment, and biofilm

A volumetric approach for determining the fouling burden on surfaces is presented, consisting of a 3D camera imaging system with fine (5 μm) resolution. Panels immersed in an estuary on the southwest coast of Florida, USA were imaged and the data were used to quantify seasonal changes in the biofouling community. Test panels, which were submerged in seawater for up to one year, were analyzed before and after gentle scrubbing to quantify the biovolume of the total fouling community (ie soft and hard organisms) and the hard fouling community. Total biofouling ranged from 0.01 to 1.16 cm3 cm−2 throughout the immersion period; soft fouling constituted 22–87% of the total biovolume. In the future, this approach may be used to inform numerical models of fluid–surface interfaces and to evaluate, with high resolution, the morphology of fouling organisms in response to antifouling technologies.