Corals in crisis: How temperature and nutrient fluctuations affect physiological responses of corals and their microbiome in K?ne‘ohe Bay, Hawai‘i

Coral reefs are the foundation of the social, cultural, and economic life in Hawai?i; however, these reefs have not escaped the conditions that have ravaged coral reefs in other areas. Along the east coast of O?ahu lies K?ne?ohe Bay, which serves as a living laboratory with distinct differences in environmental gradients due to variations in circulation and residency times. This provides a unique opportunity to explore the impact of water quality and ongoing ocean warming on coral health, susceptibility, and tolerance. Pairs of historically bleached/non-bleached corals were collected at two sites within K?ne?ohe Bay and subjected to experimental treatments varying in temperature and nutrient levels for one month at the Hawai?i Institute of Marine Biology. Biological response variables were measured, and subsamples were taken from the coral fragments at the beginning and end of the experiment for bacterial community analysis. Results demonstrate that coral decline and bleaching susceptibility were least prevalent in the Control and Elevated Nutrient treatments but most prevalent in the Elevated Nutrient + Elevated Temperature treatment, indicating that low-level nutrients may benefit the corals. Still, the combined stressors may have a synergistic, negative effect. Microbial clustering analyses reveal a shift in relative abundances of bacteria before vs. after exposure to stress. These findings may support that coral bleaching susceptibility is manifested throughout the coral holobiont and that physiological response to interactive stressors can be better understood and potentially mitigated.