Epiphytism of dinoflagellates associated with the disease ciguatera: substrate specificity and nutrition

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Abstract
Five dinoflagellate species associated with the disease ciguatera were found in abundance in the Florida Keys on one seagrass and 15 species of macro algae in the divisions Chlorophyta, Phaeophyta and Rhodophyta. One ciguatera dinoflagellate, Gambierdiscus toxicus Adachi & Fukuyo, had maximum mean abundance (2279 ± 200 cells g−1 w/w) on Heterosiphonia gibbesii (Harvey) Falkenberg (Rhodophyceae). The abundance of G. toxicus was positively correlated (r = 0.88, P < 0.01) with macroalgal surface area, of which H. gibbesii had the highest (225 cm2 g−1). Growth rates of axenic cultures of G. toxicus and the concentration of the complete, aqueous extract of H. gibbesii were positively correlated (r = 0.95, P < 0.01), with a growth rate maximum of 0.58 division day−1 at 10% of full sunlight. Growth in media supplemented with separate fractions of the extract indicated that the lipid phase promoted better growth rates than the protein/carbohydrate phase (0.34 division day−1 vs 0.26 division day−1, at 6% ...