Effects of Reduced Light and Elevated Temperature on the Zooxanthellae Concentrations and Diameters, Pigment Concentrations, and Colony Color of Montastrea cavernosa

This study measured certain biological characteristics (zooxanthellae concentrations and diameters, pigment concentrations, and colony color) of Montastrea cavernosa from the outer reef (16.8 - 26.5 m) in Broward County, FL in response to reduced light and elevated temperature stresses. The low light treatment simulated a lowering of light in the summertime (possibly associated with a turbidity increase from an event such as a hurricane, ship grounding, or dredging). The high temperature treatment was set at the maximum expected anomaly (3°C above the average summer maximum) to simulate the effect of warmer than normal seawater. The combination treatment tested for synergistic effects. Zooxanthellae concentrations and cell sizes were measured microscopically. Photosynthetic pigment (chlorophyll a, chlorophyll c, peridinin, diadinoxanthin, and β-carotene) concentrations were measured by high performance liquid chromatography. Significant decreases were found in zooxanthellae and pigment concentrations due to the elevated temperature treatments. No significant changes in zooxanthellae and pigment concentrations were observed due to the low light conditions or due to interactions from the combined stresses. Zooxanthellae cell sizes-did not change significantly, regardless of treatment. Coral color change, bleaching , was measured by a novel RGB color analysis method. Significant decreases were found in coral color due to the elevated temperature treatments. No significant changes were observed due to the low light conditions or due to interactions from the combined stresses. These results agreed with those for zooxanthellae and pigment concentrations, indicating that RGB color analysis was an acceptable, non-destructive method to quantify coral bleaching. RGB color analysis has benefits over qualitative visual observations that include (i) the reproducibility of color values despite differences in color perception and changes in ambient lighting and (ii) comparisons of color change within variable-colored coral species (e.g. Montastrea cavernosa) and between two or more species of different colors (e.g. Acropora cervicornis and Siderastrea radians)