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 previously unrecorded were identified. Our findings agree with other studies and demonstrate the frequent occurrence of the resting cysts of potentially harmful dinoflagellate species in ballast tank sediments. The lack of any clear correlation between the dinoflagellate cyst assemblage and the origin of the ballast water was ascribed to the complex nature of ballast water management on modern vessels with dedicated ballast tanks. Based on these findings, we question the scope for predicting the presence of particular harmful dinoflagellate cysts in specified ballast tank sediments for the majority of UK shipping traffic.