AME prepress abstract  -  doi: 10.3354/ame01206

ABSTRACT: The chain-forming dinoflagellate Gymnodinium catenatum is responsible for outbreaks of Paralytic Shellfish Poisoning (PSP), and the relative importance of benthic-planktonic life-cycle transitions in the appearance of blooms of this species is controversial. By coupling field and laboratory experiments, the present study is the first to analyze the dynamics of vegetative cells and sexual stages during a bloom of G. catenatum. In natural samples, the sexual stages of G. catenatum were associated with several different cellular behaviors and morphologies. This confirmed laboratory evidence for the reversibility of G. catenatum’s sexual processes and for the ability of zygotes to either bypass or shorten the route to resting-cyst formation. Moreover, chains of up to four viable cysts with different morphology never reported before for this species were observed. At least two of the cysts had reticulated surfaces; a feature related to sexual reproduction in previous studies, implying the involvement of sexual processes not possible to explain by any route depicted before for this species. The morphological variability and abundance of the sexual stages during the bloom indicated respectively the complexity of G. catenatum sexual cycle and the important role of sexual reproduction in the ecological succession of this species. However, the lack of a dormancy period in the sexual resting stage, evidenced by the large number of germinated cysts recorded in sediments sampled 3 months after the bloom, indicated that incoming of off-shore populations, rather than seed beds, are the main factor explaining G. catenatum blooms in the Galician rías.