UC San Diego

Coral reefs have been affected in the past few decades by a number of anthropogenic environmental stresses, and have suffered unprecedented declines in areal extent, live coral cover, and individual colony health. One primary factor affecting reefs has been increased thermal stress from higher water temperatures. Thermal stress is a principal environmental trigger, and increases the severity and extent of coral bleaching, a physiological response where the symbiotic zoozanthellae in the corals are expelled. Coral bleaching is stressful to corals, and can result in rapid total or partial coral colony mortality. Furthermore, long-term impacts from these stress events are possible even after colony recovery. Post-disturbance recovery trajectories are not well defined for different scleractinian species, and are difficult to determine, given the extremely slow growth rates for scleractinian corals. Differential recovery trajectories following thermal disturbance could result in a severely altered coral community makeup over decadal time scales, affecting ecosystem sustainability and decreasing the economic services rendered by these systems. In 2005 much of the Caribbean Basin was subjected to a very intense coral bleaching event. Aspects of this bleaching event and the effects on the coral community in Bocas del Toro, Panama are investigated in this dissertation. Specifically I investigate the hydrographic and oceanographic structure leading to the thermal event, the long-term impact on coral survivorship and growth as determined through analysis of changes in the planar area of live coral tissue for individual colonies, and the effect of the disturbance event on the intracellular diversity of clades of the dinoflagellate of the genus Symbiodinium, which are obligate coral symbionts. This thesis provides an integrated long-term perspective of the oceanographic, organismal, and molecular realms as they relate to the community of hard corals in this location and provides an indication of how these reef communities might respond to forecasted future global increases in the severity and occurrence of thermal stress events