| Ciguatera is the most frequently reported marine toxin disease in the world; however, the ecological and physiological factors underlying toxicity are not well known. This dissertation describes research in three areas fundamental to understanding the preponderance of ciguatera: the biodiversity of ciguatera dinoflagellates, phylogeography of Gambierdiscus toxicus, and herbivore digestive mechanisms.; The ecology of ciguatera dinoflagellates was examined at Johnston Atoll to determine how habitat, water motion, and depth correlate with biodiversity. Total dinoflagellate abundance was positively correlated with depth and negatively correlated with water motion. Prorocentrum spp. and G. toxicus were dominant in lagoon/channel habitats and Ostreopsis spp. were dominant in reef crest/back reef habitats; furthermore, habitat separation existed between Ostreopsis and Prorocentrum species. These results further demonstrate that patterns of abundance, community composition and species associations documented in the Caribbean also exist in the Pacific.; Genetic and morphological variability in G. toxicus was examined to determine if heterogeneous patterns of toxicity originate from multiple genetic strains. A new method of extracting DNA from single microalgal cells was developed for this research. The large and small-subunit ribosomal DNA phylogenies showed that G. toxicus comprises four distinct lineages, one of which is also morphologically distinct. The remaining clades are morphologically homogeneous and may represent cryptic species. The taxonomic classification of Gambierdiscus spp. based on epithecal features is not supported, suggesting that a taxonomic revision to this genus is appropriate.; Marine herbivorous fishes with different alimentary physiologies were examined to determine if digestive mechanisms contribute to toxicity. The effects of gastric lysis and mechanical disruption were simulated followed by direct examination of G. toxicus cell digestibility using fishes in aquaria. Cell fragmentation was highest in scarids; however, most cells in the gastrointestinal tract of all fishes were intact, regardless of digestive morphology. This study suggests that ingestion rates are more important than digestive morphology in explaining patterns of toxicity in herbivores.; These results are relevant to understanding environmental patterns of toxicity and suggest that localized toxicity originates from both the molecular and ecological composition of the benthic dinoflagellate community and ingestion rates of herbivorous fishes. |
