Defense Date

8-8-2025

Document Type

Thesis

Degree Type

Master of Science

Degree Name

Marine Science

First Advisor

Dorothy Ellen Renegar

Second Advisor

Rob Holland

Third Advisor

Richard Dodge

Keywords

Keywords: Dispersants, Coral Reefs, Herding Agents, ThickSlick 6535, Corexit 9500a, Acute Toxicity, NOEC, LOEC.

Abstract

Coral reefs are biodiverse coastal ecosystems at risk of exposure to spilled oil; spills reaching shorelines can damage corals, mangroves, and many other species in nearshore shallow-water tropical environments. Efforts to remediate such spills have evolved over the years through the introduction of various chemical response agents that efficiently and effectively control the spread of oil. Chemical herding agents and dispersants, which can contain and control the oil spread, are promising additions to the spill response toolbox as potential alternatives to other response methods. These response agents are designed to be biodegradable and minimize potential harm to aquatic ecosystems. However, the oil spill response community needs data about the aquatic toxicity of these agents to assess their usefulness in sensitive ecosystems such as coral reefs, where other chemical agents, such as dispersants, are not typically authorized for use. To address this need, the acute toxicity of the herder Thickslick 6535 and the dispersant Corexit 9500 to two species of shallow water Atlantic scleractinian corals (Acropora cervicornis and Porites divaricata) was assessed using 96-hour static renewal tests. The 96-hour acute herder exposure thresholds (LC50) were 285.1 mg/L for Acropora cervicornis and 329.5 mg/L for Porites divaricate and the acute dispersant exposure thresholds were 9.52 mg/L for Acropora cervicornis and 27.08 mg/L for Porites divaricate. These results provide new data on the effects of herders on shallow-water corals to support spill-response decision-making and inform Net Environmental Benefit Analysis (NEBA)/Spill Impact Mitigation Assessment (SIMA).

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