Use of Microplate Respirometry to Measure Respiration of Individual Adult Coral Polyps Exposed to Deepwater Horizon Oil

of a thesis at the University of Miami. Thesis supervised by Professor Andrew Baker. No. of pages in text. (46) The Deepwater Horizon (DWH) blowout of 2010 exposed many coastal and marine ecosystems in the Gulf of Mexico (GoM) to the acute and chronic effects of crude oil. To date, no studies have investigated the toxicity of DWH oil on shallow reef-building corals despite the relative proximity of some reef sites to the DWH (Flower Garden Banks, TX) and the potential for downstream oil transport to other more distant sites (Pulley Ridge and Florida Keys, FL). In this study, we investigated the effect of acute DWH oil exposure on reef corals, both alone and in combination with elevated temperature, to determine whether seasonal warming and/or climate change might interact with toxicity. We used a novel 24-well optical fluorescence oxygen-sensing system (microplate respirometer) to measure respiration rates of individual polyps of the common Caribbean coral, Siderastrea siderea, in response to a 48 h exposure to 4% of a 1g/L HEWAF dilution of surface oil from the DWH blowout at 25C and 30C, and used an Imaging Pulse Amplitude Modulated Fluorometer (I-PAM) to measure photochemical efficiency of algal symbionts (Symbiodinium spp.). Experimental polyps were first acclimated to the experimental chambers for 7 days at 25C until the baseline respiration rates stabilized. Temperatures in the heated treatment were then raised to 30C over a 3-day period and all of the corals (including controls at 25C) were exposed to oil on day 11. After 48 h of oil exposure corals were returned to clean seawater and maintained at 25C or 30C for 48 h of respiration measurements during recovery and an additional two weeks of visual monitoring. Overall, we found that respiration rates only significantly increased in corals exposed to both oil and high temperature, and these corals showed significant morbidity after 48 h of recovery (and high rates of mortality after a further two weeks). Changes in photochemical efficiency followed similar trends as respiration, suggesting oil affected both the coral host and its algal symbionts. These findings suggest that oil exposure may be more damaging to corals during the warmer summer months, but are likely conservative because we did not include the dispersant (Corexit) as a factor in the study, which has also been shown to be toxic to marine organisms (Incardona, 2004; Shafir et al., 2007; Goodbody-Gringley, 2013; Pie, 2015). This is the first study to have investigated the combined effects of DWH oil and elevated temperature on shallow reef-building corals, and is also the first to use a microplate respirometer to measure the respiration of individual coral polyps.