Microorganisms in ballast water: Disinfection, community dynamics, and implications for management

Highlights: • Special focus has been placed on bacteria and consequences for ecosystem processes. • Disinfection involves an increase in biological availability of organic matter. • In most cases, after a successful disinfection, subsequent recolonization takes place. • Recolonization after disinfection induces a change of bacterial communities. • Invasive potential might be affected by natural and anthropogenic changes in recipient waters. -- Abstract: Increasing concerns have accelerated the development of international regulations and methods for ballast water management to limit the introduction of non-indigenous species. The transport of microorganisms with ballast water has received scientific attention in recent years. However, few studies have focused on the importance of organisms smaller than 10 μm in diameter. In this work, we review the effects of ballast water transport, disinfection, and the release of microorganisms on ecosystem processes with a special focus on heterotrophic bacteria. It is important to evaluate both direct and indirect effects of ballast water treatment systems, such as the generation of easily degradable substrates and the subsequent regrowth of heterotrophic microorganisms in ballast tanks. Disinfection of water can alter the composition of bacterial communities through selective recolonization in the ballast water or the recipient water, and thereby affects bacterial driven functions that are important for the marine food web. Dissolved organic matter quality and quantity and the ecosystem status of the treated water can also be affected by the disinfection method used. These side effects of disinfection should be further investigated in a broader context and in different scales (laboratory studies, large-scale facilities, and on the ships).