Sub-lethal coral stress: detecting molecular responses of coral populations to environmental conditions over space...

In order for sessile organisms to survive environmental fluctuations and exposures to pollutants, molecular mechanisms (i.e. stress responses) are elicited. Previously, detrimental effects of natural and anthropogenic stressors on coral health could not be ascertained until significant physiological responses resulted in visible signs of stress (e.g. tissue necrosis, bleaching). In this study, a focused anthozoan holobiont microarray was used to detect early and sub-lethal effects of spatial and temporal environmental changes on gene expression patterns in the scleractinian coral, Montastraea cavernosa, on south Florida reefs. Although all colonies appeared healthy (i.e. no visible tissue necrosis or bleaching), corals were differentially physiologically compensating for exposure to stressors that varied over time. Corals near the Port of Miami inlet experienced significant changes in expression of stress responsive and symbiont (zooxanthella)-specific genes after periods of heavy precipitation. In contrast, coral populations did not demonstrate stress responses during periods of increased water temperature (up to 29°C). Specific acute and long-term localized responses to other stressors were also evident. A correlation between stress response genes and symbiont-specific genes was also observed, possibly indicating early processes involved in the maintenance or disruption of the coral-zooxanthella symbiosis. This is the first study to reveal spatially- and temporally-related variation in gene expression in response to different stressors of in situ coral populations, and demonstrates that microarray technology can be used to detect specific sub-lethal physiological responses to specific environmental conditions that are not visually detectable.