The true origin of ciguatera poisoning was elucidated in the mid 1970s and involves a benthic unicellular dinoflagellate, Gambierdiscus spp., whose populations preferentially grow on algal "turf" that cover damaged reef ecosystems. The genus Gambierdiscus is widely spread around the globe. To date, at least 18 species of Gambierdiscus are discribded worldwide: G. australes, G. balechii, G. belizeanus, G. caribaeus, G. carolinianus, G. carpenter, G. cheloniae, G. excentricus, G. holmesii, G. honu, G. jejuensis, G. lewisii, G. lapillus, G. pacificus, G. polynesiensis, G. scabrosus, G. silvae, G. toxicus.

Cells of the benthic dinoflagellate Gambierdiscus spp. (A): Optical microscope view ; B): Scanning electron microscope view.

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Under the influence of environmental factors, generally related to natural events (hurricanes, tsunami…)  or anthropogenic activities (pollution, constructions...), populations of Gambierdiscus, already present in the environment, will proliferate.

For unclear reasons, only some strains of this dinoflagellate have the ability to produce ciguatoxins. In other terms, it is not the presence of high densities of Gambierdiscus that is responsible for ciguatera, but the strains present in the environment.

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The massive colonization of the coral reef ecosystem by Gambierdiscus toxic strains constitutes the starting point of the reef’s food chain contamination. CTXs produced by the dinoflagellate are gradually accumulated in herbivorous fish when they graze on the microalgal turfs covering damaged or dead corals. The transfer of theses toxins to carnivorous fish occurs though predation, when carnivorous fish prey on contaminated herbivorous fish. Note that some invertebrates also bioaccumulate CTXs by filtration or grazing. The bioaccumulation of CTXs is associated to a biotransformation to more toxic compounds that lead to the poisoning in humans, which are at the top of the food chain.In total, about 400 fish species have been implicated in CP events.

Note that a new genus of ciguateric dinoflagellate, called Fukuyoa, has been identified. Do date, 3 species are known: F. yasumutoi, F. paulensis and F. ruetzeli.

 Global distribution of Gambierdiscus and Fukuyoa species.