Investigation of Antioxidant Defense Profiles and Stress Responses in Hawaiian Pocillopora damicornis

Abstract

In order to improve development and refinement of molecular biomarkers for the evaluation of sub-lethal levels of stress in corals, this research provides a comprehensive characterization of baseline cycling of oxidative stress defenses in the coral Pocillopora damicornis and their responses to a natural cycle of thermally-induced bleaching. Such antioxidant enzymes are highly valuable as biomarkers for detecting stress under a wide breadth of stressors, and with global degradation of coral reefs occurring due to increasing instances of stressors implicated in oxidative stress, investigation of these biomarkers for specific tailoring towards coral health evaluations is critical. Further, through the investigation of these enzymatic responses to thermal stress, we aim to provide insight into oxidative stress responses of Pocillipora damicornis to thermal stress, which is tied to oxidative stress in corals and has become prominent, causing high levels of global coral bleaching and mortality, within the last decade. This work investigated cycling of antioxidant enzymes during coral reproductive cycles, responses of these enzymes to a thermal stress event resulting in mass coral bleaching, and whether P. damicornis preferentially shifts symbiont clade mutualisms to increase thermal tolerance following thermally-induced bleaching. Resultant from these data, this research suggests that reproduction has a significant effect on the activity of catalase, superoxide dismutase, glutathione peroxidase, and glutathione reductase. Further, enzymatic activity assays demonstrated significant increases in catalase activity with relation to heat-induced coral bleaching, although all other enzymes experienced no significant activity shifts. Finally, findings analyzing the potential for P. damicornis to shift symbiont clade assemblages from pre- to post-bleaching cycles suggests that this coral species favors conserving existing mutualisms. Such conclusions aid the molecular coral biology community through refining existing tools for detecting and characterizing sub-lethal stress levels in corals.