Effects of depth, habitat, and water motion on the abundance and distribution of ciguatera dinoflagellates at Johnston Atoll, Pacific Ocean

A major impediment to understanding the seemingly random occurrence of ciguatera toxicity is uncertainty regarding the field ecology of benthic dinoflagellates that introduce toxins into the coral reef food web. Although broad generalizations have been made, past studies have often yielded contradictory results, particularly between ecological patterns documented in the Pacific versus the Caribbean. This study employed standardized methodology to investigate the distribution and abundance of toxigenic benthic dinoflagellates from the genera Gambierdiscus, Prorocentrum, Ostreopsis, and Amphidinium at Johnston Atoll, Pacific Ocean, to determine how water motion, depth and habitat type influence patterns of biodiversity. Sampling stations located in lagoon and channel habitats in the atoll supported the highest total dinoflagellate abundance, while dinoflagellate numbers were lower at sampling stations in back reef and reef crest habitats. Total dinoflagellate abundance was primarily determined by the degree of water motion; however, this effect varied among genera. Of the 4 genera surveyed, 3 (Gambierdiscus, Prorocentrum, Amphidinium) were negatively correlated with water motion; conversely, Ostreopsis had a positive correlation. Habitat separation was observed between Ostreopsis and Prorocentrum spp., which were negatively correlated. Gambierdiscus was present at all sampling stations and at all habitats, even though it was rarely the dominant genus. This study provides a characterization of the ciguatera dinoflagellate community across a variety of coral reef habitats, contributing to an accurate and coherent characterization of the population dynamics of this important dinoflagellate community.