Description of two new species Chattonella tenuiplastida sp. nov. and Chattonella malayana sp. nov. (Raphidophyceae) from South China Sea, with a report of wild fish mortality

Fisheries damage caused by Chattonella red tide has been recorded in Southeast Asia. Molecular studies have clarified the presence of two species, Chattonella marina complex and Chattonella subsalsa in the region, unlike East Asia that had only C. marina complex. To elucidate the phylogeography of Chattonella in Asia, further phylogenetic and morphological examinations were carried out with 33 additional culture strains, including the strains isolated during a bloom of Chattonella sp. (up to 142 cells mL(-1)) that was associated with a wild fish mortality along the northeastern coast of Peninsular Malaysia in 2016, and those from Yellow Sea, where the Chattonella genotypes have not been determined. LSU rDNA and ITS2 trees showed five intrageneric clades in the genus Chattonella, which were clades I and II (C. subsalsa), Glade III (C. marina complex) and two new clades, namely Glade IV from Thailand and Malaysia, and Glade V from Peninsular Malaysia. The positions of the two new clades were different in LSU rDNA and ITS2 trees. LSU rDNA divergences of clades IV and V from the other clades were >= 4.01% and >= 5.70%, while their ITS2 divergences were >= 7.44% and >= 16.43%, respectively. Three and five compensatory base changes (CBCs) were observed in the clades IV and V, respectively, when compared to each of their closest Glade. Cells from clades IV and V showed similar morphology to C. marina complex and C. subsalsa Glade II, including the presence of button-like granules on cell surface and oboe-shaped mucocysts. However, cell size, the number and shape of chloroplasts in Chattonella clades IV and V, and the nonstacked thylakoids penetrated the pyrenoid in C. subsalsa Glade II, were distinctive. Based on the diagnostic chloroplast shape, we proposed the designation of clades IV and V to two new species, Chattonella tenuiplastida sp. nov. and Chattonella malayana sp. nov.