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1989. Epiphytism of dinofl agellates associated with the disease ciguatera: substrate specifi city and nutrition. Phycologia 28: 360-368.Five dinofl agellate 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 max imum mean abundance (2279 ± 200 cells g-I 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-I). 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-I 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-I vs 0.26 division day-I, at 6% of full sunlight). The Zn2+ concentration of K medium could be increased to a normally toxic level (2.4 x 10-7 M) without adverse effects as long as extract was present, and growth in the lipid fraction was the least affected. Free nitrate, phosphate and ammonia concentrations in the extract were negligible, indicating that the extract probably functions primarily as a chelator.

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Seventeen clones of the ciguatera‐causing dinoflagellate Gambierdiscus toxicus Adachi and Fukuyo were acclimated to the same environments over several months. Significant variance components were detected between non‐acclimated and acclimated cultures for cell potencies, yields and reproduction rates. The resultant variance in acclimated potencies among clones was statistically significant (P < 0.0001), indicating that potency can be used for genetic comparisons. However, cell potency differences for a clone of G. toxicus in the acclimated vs. non‐acclimated phases can exceed genetic differences between clones. This stresses the need for a rigorous acclimation process. Caribbean isolates of G. toxicus were inherently more toxic than isolates from other areas. One Caribbean clone yielded 55 × 10−4 mu (mouse units)·cell−1 whereas clones Bermuda, the Bahamas, and Florida ranged from only 1.8 × 10−4 mu·cell−1 to a maximum of 19.8 × 10−4 mu·cell−1. Toxicity decreased with increasing latitude (r =–0.819, P < 0.01), indicating that environmental differences probably influenced the potencies. A comparison of acclimated reproduction rates at four light intensities also indicated that genetic differences among clones existed. The resulting reproduction rate/light slopes overlapped, indicating that the clones may be adapted to specific light regimes.

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