Effect of Louisiana sweet crude oil on a Pacific coral, Pocillopora damicornis

•Tissue regeneration of a shallow-water, branching coral was significantly reduced after a 96 h exposure to a crude oil HEWAF.•Percent tissue regeneration was negatively correlated with exposure duration during short-term exposures.•Chlorophyll a fluorescence of the algal symbiont decreased following oil exposure.•Polyp behavior (retraction) was the driver for reduced gross health assessments in oil-exposed coral. Recent oil spill responses such as the Deepwater Horizon event have underscored the need for crude oil ecotoxicological threshold data for shallow water corals to assist in natural resource damage assessments. We determined the toxicity of a mechanically agitated oil-seawater mixture (high-energy water-accommodated fraction, HEWAF) of a sweet crude oil on a branched stony coral, Pocillopora damicornis. We report the results of two experiments: a 96 h static renewal exposure experiment and a “pulse-chase” experiment of three short-term exposure durations followed by a recovery period in artificial seawater. Five endpoints were used to determine ecotoxicological values: 1) algal symbiont chlorophyll fluorescence, 2) a tissue regeneration assay and a visual health metric with three endpoints: 3) tissue integrity, 4) tissue color, and 5) polyp behavior. The sum of 50 entrained polycyclic aromatic hydrocarbons (tPAH50) was used as a proxy for oil exposure. For the 96 h exposure dose response experiment, dark-adapted maximum quantum yield (Fv/Fm) of the dinoflagellate symbionts was least affected by crude oil (EC50 = 913 μg/L tPAH50); light-adapted effective quantum yield (EQY) was more sensitive (EC50 = 428 μg/L tPAH50). In the health assessment, polyp behavior (EC50 = 27 μg/L tPAH50) was more sensitive than tissue integrity (EC50 = 806 μg/L tPAH50) or tissue color (EC50 = 926 μg/L tPAH50). Tissue regeneration proved to be a particularly sensitive measurement for toxicity effects (EC50 = 10 μg/L tPAH50). Short duration (6−24 h) exposures using 503 μg/L tPAH50 (average concentration) resulted in negative impacts to P. damicornis and its symbionts. Recovery of chlorophyll a fluorescence levels for 6−24 h oil exposures was observed in a few hours (Fv/Fm) to several days (EQY) following recovery in fresh seawater. The coral health assessments for tissue integrity and tissue color were not affected following short-term oil exposure durations, but the 96 h treatment duration resulted in significant decreases for both. A reduction in polyp behavior (extensi