Does Eutrophication Play a Role in Ciguatera Fish Poisoning?

Ciguatera fish poisoning (CFP) is a circumtropical seafood poisoning caused by the ingestion of marine fish (especially reef fish) that have accumulated toxins (ciguatoxins) produced by species of the benthic dinoflagellate genus, Gambierdiscus.  Recent estimates suggest that globally, one million people may be affected by CFP annually.  Cases of CFP, however, appear to be increasing, leading some to wonder what role human activities play in ciguatera.  The role played by nutrients in CFP has been understudied and remains unclear.  Gambierdiscus may not respond directly to nutrient enrichment, as they are primarily epiphytic, likely obtaining nutrients from its algal host or co-occurring epiphytes.  The most likely role of eutrophication in CFP is coral reef degradation, which can lead to a greater abundance of macroalgae and therefore more substrate for toxigenic dinoflagellates.  Additionally, an increase in nutrient inputs can alter macrophytic species assemblages (generally coupled with grazing pressures).  If the resultant species assemblage is more favorable to toxic, epiphytic dinoflagellates and more palatable to grazers, the resultant trophic transfer of the toxins into the benthic food web could increase as well.  Therefore, the role of eutrophication in CFP cannot be considered solely; host- and grazing factors must also be considered.