Harmful dinoflagellate resting cysts in ships' ballast tank sediments: potential for introduction into English and Welsh waters

Abstract Sediment samples taken from ballast tanks of ships in English and Welsh ports were examined for the presence of dinoflagellate resting cysts. Cysts with apparently viable cell contents, identifiable to at least genus level, were found in 69% of samples; 48 species were identified, representing 20 genera. A maximum of 22 cyst types were found in a single sample, but most samples contained less than five. Maximum recorded cyst concentration was 8950 cysts ml−1 wet sediment. The majority of samples contained < 400 cysts ml−1. Potentially harmful cyst types included toxic, bloom-forming, and non-indigenous species. Alexandrium species were recorded in 25% of samples, A. tamarenselcatenella cysts being the most common, occurring in 17% of samples. In addition to the germination of observed cysts, slurry enrichments also produced motile stages of smaller species unrecorded in microscopical surveys. Most cyst types found in this study have been recorded from UK waters, although a number of species previ...