Characterizing the Innate Immunity in the Hawaiian Coral Montipora capitata

Coral reefs are among the most diverse ecosystems in the world; however, they are quickly diminishing due to natural and anthropogenic stressors, including disease. Corals possess innate immune responses that aid in protection against these stressors. In several coral species, immune responses are inducible in response to stress. Montipora capitata is a predominant coral in Kaneohe Bay, Oahu, Hawaii. This coral occurs in two color morphs, orange and red, and is susceptible to the tissue loss disease Montipora white syndrome (MWS). MWS disease prevalence within Kaneohe Bay varies, with lower prevalence in the North than South Bay and with orange colonies more susceptible than red colonies. To begin to characterize the immune system of M. capitata, I measured baseline activity of prophenoloxidase (PPO), superoxide dismutase (SOD), catalase (CAT), and peroxidase (POX), and melanin concentrations, in natural populations of red and orange M. capitata colonies from the North and South Bay. I also assessed immune activity in healthy and natural diseased pairs of orange colonies from Kaneohe Bay. To test inducibility of these immune responses, orange and red colonies from the North and South Bay were exposed to a bacterial pathogen associated with MWS in a laboratory challenge experiment. Overall, constitutive immune activity varied, with corals from the North Bay exhibiting higher levels than the South Bay. In the infection experiments, several orange colonies developed MWS, but red colonies did not. South Bay colonies exposed to the MWS pathogen shominor reductions in immune activity. In the North Bay corals, immune enzyme activity increased in both color morphs exposed to a non-pathogenic bacterium; however, activity was depressed when exposed to the MWS pathogen. Immune activity differences, both constitutive and in challenge experiments, may be due to a diversity of host, pathogen, and environmental factors, including the types of immune responses used, water quality or environmental stress, and pathogen virulence factors. This study adds to our understanding of immune response and disease susceptibility of M. capitata in Kaneohe Bay, but more exploration is needed to further understand innate immunity in this system