Abstract
Ciguatera fish poisoning (CFP) is a global public health concern that is associated with Gambierdiscus, a genus of harmful algae found in coral reef environments that includes species known to produce toxins (ciguatoxins). Outbreaks of CFP have often been linked to elevated abundance of Gambierdiscus cells and disturbance-related degradation of coral reefs. However, the influence of human activities on CFP risk, both directly and indirectly within the broader context of reef health, has yet to be defined for highly exploited patch reefs in the Florida Keys. The objectives of this study were to define spatial and temporal patterns in reef health and Gambierdiscus abundance across the three regions (Upper, Middle, Lower), to determine whether the drivers of those patterns were natural or anthropogenic, and to identify biogeographic indicators of risk. To address these objectives, this study combined field sampling with a “big data” approach to spatial analysis. Six patch reefs (two per each of three regions) were selected as study sites from existing research stations. Datasets from long-term monitoring of benthic cover, fish species abundance, land use, and water quality were compiled and analyzed in ArcGIS to characterize the ecological context of each site. Analysis of samples of host macroalgae collected from all study sites biannually revealed that Gambierdiscus cell densities were consistently highest in the Upper Keys and lowest in the Middle Keys, regardless of season. Conversely, reef health was lowest in the Upper Keys and improved along a gradient to the Lower Keys. Multivariate analysis of site similarity indicated that this regional pattern was driven more strongly by grazing than substrate availability. Additionally, there is evidence that human activities have an indirect influence on CFP risk through reef health, as well as through overfishing, and the destruction of inshore habitats like seagrass and mangroves. Due to a strong positive correlation with cell densities, this study suggests that mangrove cover could be useful as a biogeographic indicator of potential CFP risk. Whereas surgeonfish, with a strong negative correlation with cell densities, could indicate the actual flow of toxins into higher trophic levels. The concordance of high regional risk and high population density necessitates continued monitoring of fish in those areas and the development of more comprehensive predictor of potential CFP outbreaks.