Sexual processes and life cycle transitions of the tropical Pacific Alexandrium minutum (Dinophyceae)

Abstract

SUMMARY Resting cysts of harmful marine dinoflagellates, including Alexandrium species, play an important role in their bloom dynamics, where massive cyst germination is regarded as the natural phenomenon that initiates blooms. The life cycle of Alexandrium minutum from the temperate region has been intensively studied, however, related studies on its tropical counterparts are scarce. In this study, sexual reproduction of a toxigenic A. minutum (tropical Pacific ribotype) was investigated in a laboratory setting. Gamete expression was observed in both compatible cross‐mating and self‐crossed cultures, but sexual induction was observed only in the compatible cross‐mating cultures, confirming the heterothallic nature of the species. Resting cysts were successfully produced in 41 out of 91 pairwise combinations of cross‐mating strains. The crossing matrix results showed that the mating system of the tropical Pacific A. minutum was complex, with at least four distinct mating groups observed. The resting cysts had a relatively shorter dormancy period (5–8 days). The rapid encystment‐excystment processes and a short cyst dormancy period in this tropical Pacific A. minutum are believed to play crucial roles in governing the bloom and its dynamics in the tropical coastal region.

Co-occurrence of Alexandrium minutum (Dinophyceae) ribotypes from the Chinese and Malaysian coastal waters and their toxin production

“…The cysts were described as small (24-29 µm in diameter), round in apical view and hemispherical in lateral view. Such kind of cysts were later reported in the Mediterranean Sea (ribotype A; Garcés et al, 2004;Bravo et al, 2006), and from Peninsular Malaysia (ribotype B; Liow et al, 2021). Cysts of ribotype C were also detected through HTS metabarcoding in Dongshan Bay, although its morphology has not been revealed by microscopy.…”

Apparent biogeographical trends in Alexandrium blooms for northern Europe: identifying links to climate change and effective adaptive actions

“…Species classified within the genus Alexandrium Halim may be found globally from polar seas to coastal and shelf seas at all latitudes, includingfrom brackish water, and in tropical and subtropical lagoons (Tahvanainen et al, 2012;Van de Waal et al, 2015;Anderson et al, 2021;Liow et al, 2021). The type species A. minutum Halim was described from Alexandria harbor in Egypt (Halim, 1960), where it caused water discoloration ("red tide") but was not linked to harmful events at the time.…”