Report of a bloom-forming dinoflagellate takayamaacrotrocha from tropical coastal waters of singapore

Abstract

Four clonal cultures of the unarmored dinoflagellate Takayama acrotrocha (J. Larsen) de Salas, Bolch et Hallegraeff were established from Singapore coastal water on October 20, 2004, and January 1, 2007, for a HAB monitoring project. LM and SEM observations demonstrated that the isolates were not consistent with the other five species within this genus in position of nucleus, shape of the apical groove, and number and shape of chloroplasts. New morphological observations of the Singapore isolates that were not in the type description of T. acrotrocha include a narrow and shallow slit located above the entire anterior edge of the cingulum, a tube-like structure in the sulcus, numerous multilateral plate-like surface vesicles, a sulcal intrusion into the epicone, and possibly a peduncle in between the two emerging points of flagella. The presence of sulcal intrusion into the epicone was not consistent with the type description but is prominent in SEM micrographs. Phylogenetic analysis of the partial LSU rDNA sequences indicated Singapore strains of T. acrotrocha are conspecific with two isolates from Italy, but less homologous to T. helix, T. tasmanica, and T. tuberculata. Laboratory fish bioassays using Asian sea bass (Lates calcarifer) and sheepshead minnows (Cyprinodon variegates) did not indicate fish-killing activity by this species, and to our knowledge, there were no reports of fish-kills occurring during blooms of this species in Singapore and Italy. This is the first report of T. acrotrocha from tropical waters and indicates a likely cosmopolitan distribution of the species. © 2012 Phycological Society of America.