Project Overview

Summary:

     Dr. Abigail Renegar at Nova Southeastern University’s Halmos College of Natural Sciences and Oceanography, was awarded an RFP-VI grant at $449,619 to conduct the RFP-VI project titled, “Coral-Tox: A Species-Sensitivity Assessment of Petroleum Hydrocarbon Toxicity to Scleractinian Corals”. The project consisted of 1 principal investigator (Renegar), 1 co-PIs (Dr. Jose Lopez), 1 PhD student (Nicholas Turner); 3 Masters students (Dawn Bickham, Edward Young, Eileen Whitemiller); and several research staff, data and outreach team members.

     Coral reefs are iconic ecosystems throughout the planet’s tropical belt, including Florida, the Gulf of Mexico, and the Caribbean Sea. They are valuable for their intrinsic beauty, economic and tourist value, as incubators for fisheries, and for the physical protection they provide the land against the oceans. Coral reefs are also one of the world’s most threatened resources due to a variety of environmental stressors. From the perspective of Oil Spill Preparedness and Response (OSPR), coral reefs, with particular focus on the impacts on the coral animal itself, represent one of the highest valued natural resources for protection in Net Environmental Benefit Analysis (NEBA) of response methods and environmental damage. Previous research evaluating hydrocarbon toxicity to corals and coral reefs had generally focused on community-level effects (relatively little is known at the individual and cellular level) and results were often not comparable between studies due to variability in hydrocarbon exposure characterization and evaluation of coral health/mortality during exposure. Overall, this represented an important knowledge gap in oil spill preparedness and response as it relates to the potential impact of oil spills on coral reefs.

This research was developed with input from research partners in government and the response community in order to design study outputs that would integrate with existing toxicity models and emerging 3D plume models to better inform response decision-makers on the potential impacts of hydrocarbons, and various response options, in coral reef environments. Specifically, the availability of reproducible toxicity endpoints for multiple species of scleractinian corals would support modeling of the potential effects of transported concentrations of oil or dispersed oil plumes at various distances from coral communities. The approach focused on development and application of a standardized toxicity testing protocol using single hydrocarbons, which considered coral response at multiple levels of resolution and was applicable to many coral species and test scenarios. This allowed  determination of a critical body burden (CBB) using the target lipid model, which was then used to compare species sensitivity, predict the toxicity of other hydrocarbons, and guided subsequent experimentation utilizing oil water accommodated fraction (WAF), and chemically enhanced water accommodated fractions (CEWAF). The target species were five ecologically relevant Atlantic shallow-water corals: Acropora cervicornis, Solenastrea bournoni, Stephanocoenia intersepta, Siderastrea siderea, and Porites astreoides.

The central goal of these experiments was to address the lack of knowledge which existed regarding environmental effects of the petroleum/dispersant system on scleractinian corals, which are key coastal organisms (Theme 3). This new information would then allow determination of thresholds of acceptable/unacceptable impact, and prediction of impact severity and choice of treatment based on expected impact. The sum of experimental results, when integrated into existing/emerging response support tools, would provide input to managers for the visualization, prediction, and understanding of oil impacts on key organisms and specific habitats, significantly improving response. This applied science approach to a practical issue improves decision-frameworks for reaction, response and mitigation should an oil spill potentially impact coral reefs (Theme 4).

Research Highlights

     Dr. Renegar’s research, which included 28 outreach products and activity, with 6 pending publications, 5 scientific conference presentations, and 18 datasets submitted to the GoMRI Information and Data Cooperative (GRIIDC), which are available to the public.  Significant outcomes of their research (all related to GoMRI Research Theme 3 and 4) are highlighted below.

Experiments with toluene, 1-methylnaphthalene, and phenanthrene found a variable range of species-specific physical responses to petroleum hydrocarbon exposure, with greater impacts observed in branching corals compared to massive corals. Overall, all five tested scleractinian coral species were relatively resilient to petroleum hydrocarbon exposure compared to other coastal marine organisms. Subsequent experiments with the two species identified as the most sensitive, A. cervicornis and P astreoides, indicated that both were minimally impacted by exposure to oil WAF, which was consistent with species sensitivity comparisons based on the single hydrocarbon results. Exposure to oil  CEWAF resulted in more severe effects (including mortality) due to the higher hydrocarbon concentrations in the water caused by the use of dispersant, however the toxicity of oil and dispersed oil was comparable at oil loadings below 125.5 mg/L.

 A key part of this project was the use of multiple metrics to evaluate coral response to petroleum hydrocarbon exposure. Corals exhibited a range of physical responses; when exposed to low hydrocarbon concentrations (or high concentrations over short time scales) polyp retraction, elevated mucus production, and tissue swelling was frequently observed. At higher concentrations, responses included tightly retracted polyps and bleaching; highly stressed corals had severe polyp retraction, tissue loss and mortality. Significant reductions in photosynthetic efficiency of the corals’ symbiotic zooxanthellae was also a frequent effect of hydrocarbon exposure.

Assessment of sublethal effects from low levels of exposure can be more important for determining the impacts of petroleum spills in the environment, particularly for organisms such as corals that that may already be affected by other stressors. The earliest and most sensitive biomarkers for physiological responses to stress are likely in the transcriptome, where physiological effects of contaminants may be expressed prior to the onset of physical changes. For A. cervicornis, the hydrocarbon concentrations which resulted in a significant change in gene expression were nearly an order of magnitude lower than the hydrocarbon concentrations which resulted in significant sublethal physical changes. While the reason for the relative resilience of corals has not been conclusively identified, it may be related to coral's large tissue lipid reserves and ability to secret mucus. This is supported by the gene expression analysis, which indicated upregulation of cellular machinery associated with detoxification and depuration.

The scientifically defensible toxicity thresholds determined by the Coral-Tox project have meaningfully expanded our knowledge on the effects of petroleum hydrocarbons on scleractinian corals, and provided needed validation of the results of complementary research, such as the TROPICS field study. Importantly, this new information on the effects of oil and dispersed oil exposure on shallow-water corals has already been utilized in NEBA assessments and oil spill preparedness exercises. The next step forward in improving spill response decision-making is to broaden our understanding of how coral resilience to oil exposure is altered by the impacts of a changing environment on increasingly vulnerable coral reef ecosystems.

 Proposal Abstract - RFP-VI PI Abigail Renegar