Ecology and Epizootiology of Montipora White Syndrome, A Tissue Loss Disease of the Hawaiian Coral, Montipora capitata

Abstract

Coral reefs are among the most productive and biologically diverse ecosystems on Earth. Corals are the keystone species that protect coastal land, provide beach sand, and drive industries such as tourism and fisheries. However, coral reef ecosystems are declining at an alarming rate, primarily due to coral diseases. Diseases in coral, like any other organism, result from a complex interaction between host resistance, pathogen interactions, and environmental cofactors. Montipora White Syndrome (MWS) is a progressive tissue loss disease that primarily affects Montipora capitata, an abundant reef-building coral in Hawaii. Montipora capitata occurs in two color morphs, red and orange, that coexist on reefs. The red color morph is numerically dominant on reefs, yet the orange morph has the highest MWS prevalence. The dichotomy observed among the color morphs of M. capitata presents a unique opportunity to examine the aspects of host physiology that contribute to disease resistance. The main objectives of this dissertation were to investigate the epizootiology of Montipora White Syndrome in terms of differential disease susceptibility, mechanisms of pathogen exposure, and environmental triggers of outbreaks. Red and orange morphs of M. capitata were found to have different mucus-associated bacterial communities, which may be a factor driving differential disease susceptibility. Bacterial pathogens of MWS were detected in multiple biotic and abiotic sources, suggesting that corals are frequently exposed to MWS pathogens. Finally, an acute stressor correlated to past MWS outbreaks (lowered salinity due to heavy rain events) was found to lower the dosage of pathogen needed to cause MWS in a laboratory setting. The information gained from this research will help us understand how corals resist or succumb to disease and will help us determine how this Hawaiian coral disease can be managed in the future.