Phylogeny, morphology and toxicity of benthic dinoflagellates of the genus Fukuyoa (Goniodomataceae, Dinophyceae) from a subtropical reef ecosystem in the South China Sea Priscilla T.Y. Leung a,b , Meng Yan a,b , Veronica T.T. Lam a , Sam K.F. Yiu a , Chia-Yun Chen a , J. Sam Murray c , D. Tim Harwood c , Lesley L. Rhodes c , Paul K.S. Lam a,b,d, *, Tak-Cheung Wai a,b, * a State Key Laboratory in Marine Pollution, City University of Hong Kong, Hong Kong, China b Research Centre for the Oceans and Human Health, City University of Hong Kong Shenzhen Research Institute, Shenzhen, China c Cawthron Institute, Nelson, New Zealand d Department of Chemistry, City University of Hong Kong, Hong Kong, China A R T I C L E I N F O Article history: Received 28 February 2018 Received in revised form 7 March 2018 Accepted 8 March 2018 Available online 17 April 2018 Keywords: Ciguatera Gambierdiscus Coral and rocky reefs Toxic epiphytic algae CTX and MTX A B S T R A C T Species of Fukuyoa, recently revised from the globular Gambierdiscus, are toxic benthic dinoflagellates associated with ciguatera. In this study, a total of ten strains of Fukuyoa collected from Hong Kong waters were characterized using morphological and phylogenetic analyses. Results from both analyses showed that one of the strains is a putative new species, namely Fukuyoa sp. HK Type 1 (plate formula Po, 3 0 , 7 00 , 6c, 7s, 5 000 ,1p and 2 0000 with a distinctive small and narrow cell shape, narrow Po plate, high Po pore density, large and broad Plate 1 0 but small and round Po pore size, small and narrow Plate 2 0 , long and narrow Plates 2 0000 and 1p), and the others were F. ruetzleri. This is the first report of these two species of Fukuyoa in the South China Sea and Asia-Pacific region. Phylogenies on 18S, 28S D1/D3 and D8/D10 ribosomal DNA sequences strongly support that Fukuyoa sp. HK Type 1 is currently the most divergent species in the genus Fukuyoa. The diagrammatic plots on the p-distance matrices of 18S, 28S D1/D3 and D8/D10 and ITS regions resolved that the species of Fukuyoa were separated into three main groups, i.e., Fukuyoa sp. HK Type 1, F. paulensis and a group consisting of F. ruetzleri, F. yasumotoi and F. cf. yasumotoi, while Fukuyoa sp. HK Type 1 was always the most distant from the other two groups. Additionally, the pairwise p-distance values calculated based on the ITS region have always been the highest for pairs between Fukuyoa sp. HK Type 1 and other Fukuyoa species, ranging from 0.142 to 0.150. Our molecular results suggested that Fukuyoa sp. HK Type 1 is a putative new species. Both morphological and molecular data of more strains from different localities should be, however, collected to address its intraspecific variability and further evaluate its taxonomic status. A bioassay analysis demonstrated that algal lysates extracted from F. ruetzleri and Fukuyoa sp. HK Type 1 were lethal to brine shrimp larvae, indicating that both species were toxic. Bulk cultures were tested for Pacific ciguatoxins (P-CTXs) and maitotoxins (MTXs) by liquid chromatography-tandem mass spectrometry (LC–MS/MS). All isolates of Fukuyoa produced neither P-CTXs nor MTX-1, but isolates of F. ruetzleri produced a compound putatively assigned as MTX-3. This study has updated the current biodiversity and distribution of the toxic benthic dinoflagellates Fukuyoa, and thus contributes to the understanding of their emerging threats to the sub-tropical reef systems locally and regionally. © 2018 Elsevier B.V. All rights reserved. 1. Introduction Species of Gambierdiscus are marine benthic dinoflagellates which have been receiving global attention because they are known as the main producers of the ciguatoxins (CTXs), a group of potent neurotoxins that are associated with ciguatera fish poisoning (CFP) in humans through consumption of CTX-contami- nated fish (Fleming et al., 1998; Lehane and Lewis, 2000; Chinain * Corresponding authors at: State Key Laboratory in Marine Pollution, City University of Hong Kong, Hong Kong, China. E-mail addresses: bhpksl@cityu.edu.hk (P.K.S. Lam), waitakcheung@hotmail.com (T.-C. Wai). https://doi.org/10.1016/j.hal.2018.03.003 1568-9883/© 2018 Elsevier B.V. All rights reserved. Harmful Algae 74 (2018) 78–97 Contents lists available at ScienceDirect Harmful Algae journal home page : www.elsevier.com/locat e/hal