Coral Cover and Algae Growth Along a Water Quality Gradient in Moorea, French Polynesia

Abstract

As climate change and anthropogenic perturbations cause dramatic shifts in coral reef ecosystems, it is of increasing importance to understand corals’ tolerance, response, and adaptation to a combination of stressors. Nutrient enrichment increases the sensitivity of corals, making them more prone to bleaching from thermal stress. In Moorea, French Polynesia, Cook’s Bay is more developed and potentially more impacted by nutrient runoff from sewage and agriculture than its neighbor, Opunohu Bay. To assess the ecological gradient and level of human disturbance along these two central bays in Moorea, this study surveyed coral diversity by genera, percent coral cover, percent bleached coral cover, macroalgae cover, and nutrient-treated coral transplants in five sites surrounding the two bays. The site in between the two bays was the most ecologically diverse and rich, significantly differing from the Cook’s Bay sites as it had a greater average total coral cover. When Pocillopora verrucosa fragments were transplanted to each of the varying environments at the sites, in which some were treated experimentally with a nutrient diffuser at a different field-site prior to this study, treatment transplants experienced more bleaching than the control. This study supports previous research surrounding anthropogenic nutrient enrichment and its effects on coral reef ecosystems, while exploring the complex interactions among the various factors that impact coral resilience in an isolated island barrier reef. Major,