UC San Diego

In recent years Hawaiian corals have been exposed to the increasing frequency and intensity of annual warming events, nutrient pollution and overfish which has negatively impacted these holobionts through bleaching, microbial infection, and direct competition. This study focuses on reefs at two sites in Maui, Olowalu and Wahikuli. The Wahikuli site experiences elevated nutrient runoff from the nearby Lahaina Wastewater Treatment Plant. Using rRNA gene biomarkers, this study shows that the microbial communities from partially bleached Porites lobata have relatively similar compositions to their healthy counter parts regardless of site or proximity to turf overgrowth. Further analysis of the turf algae assemblages overgrowing the P. lobata colonies reveal a higher abundance of ammonia-oxidizing archaea from the family Nitrosopumilaceae in Wahikuli compared to Olowalu which indicate site-specific differences in the microbial community compositions. Nutrient pollution from land-based activities is a cause for concern because it causes shifts in the coral microbiome, reducing host fitness, while simultaneously stimulating the growth of macroalgal competitors. Combined with the increasing frequency and intensity of warming events, additional nutrient inputs diminish coral competition leading to succession from coral to algae dominated habitats.