The potential for transport of non-indigenous marine microalgae via ship's ballast water has been amply demonstrated, and nearly all known harmful algal bloom species have been documented in viable form from ship's ballast water. Ballast water uptake needs to be strongly discouraged during harmful algal bloom events. Efficacy of ballast water exchange in removing harmful microalgal cells is limited, since this nearly always leaves behind a viable inoculum. The precise location of ballast water exchange needs to be carefully chosen, and retention of dinoflagellate cysts and diatom spores in ballast tank sediments is of special concern. The only fully effective ballast water treatment for microalgae is the application of biocides, but heat treatment also offers considerable promise especially in subtropical and tropical waters. To manage harmful algal blooms, other key environmental drivers such as eutrophication and climate change also need to be addressed. Effective monitoring for harmful algal species and their toxins remains the critical tool to protect human health, fisheries, aquaculture and desalination industries. Challenges and opportunities for ballast water management in the Arabian Gulf region are discussed.

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