Abstract:

The Deepwater Horizon blowout in 2010 released an estimated 4.9 million barrels of crude oil into the Gulf of Mexico in the 83 days between the initial explosion and the capping of the well. Response included extensive use of Corexit® oil dispersant. Although South Florida was spared exposure by currents, this event highlights the need for effective bioassay organisms for coral reefs. Amphistegina spp. are benthic foraminifers that host diatom symbionts in a relationship similar to that of coral and their zooxanthellae. Amphistegina spp. occur abundantly in reef communities nearly worldwide, are easily collected and maintained in culture, and are a key component of the FoRAM Index, a indicator of water and sediment quality in coastal waters. The major goals of this project were to develop protocols to test the acute and chronic responses of A. gibbosa to potentially toxic organic chemicals. Initial objectives were to determine lethal concentrations and effects ranges, as defined by the US Environmental Protection Agency, of two components of the Corexit® dispersants. Preliminary experiments indicated that many specimens exposed to propylene glycol (v/v) at concentrations of 2% or higher appeared to be dead following 48-hour exposure, resulting in apparent LC50 of 3% and an initial effects range of 2-4%. When placed in filtered seawater, after 72-hours the observed LC50 was 6%. All parameters assessed, including sub-lethal chronic effects (differences in growth and visible responses after 40 days), revealed an effects range of 0.5% to 12%, above which there was 100% mortality. For 2-butoxyethanol, the apparent LC50 after 48-hour exposure was 0.2%; after 72-hour recovery the LC50 was 1%. In all experiments, a 72-hour recovery period was sufficient to determine acute effects. A key discovery was the observation of inactivity during exposure to toxic substances, followed by recovery when placed in filtered seawater. This observation indicates the potential for dormancy in adult foraminifers exposed to toxic substances that has not previously been reported.

Suggested Citation:

Ross, Benjamin, and Pamela Hallock-Muller. 2015. Responses to Chemical Exposure by Foraminifera: Distinguishing Dormancy From Mortality. Distributed by: GRIIDC, Harte Research Institute, Texas A&M University–Corpus Christi. doi:10.7266/N78050KD

Purpose:

This dataset was developed to quantify the acute, lethal and sublethal effects of 48-hr exposure to the chemical components of dispersants used in the aftermath of the Deepwater Horizon oil spill on Amphistegina gibbosa¸a common benthic foraminifer on the coral reefs of the Florida Keys. It also serves as a proof of concept for further research utilizing A. gibbosa as a relevant benthic organism for assaying the effects of chemical exposures on coral reefs in the Florida Keys.

Data Parameters and Units:

Data collected was primarily observational. As a result, it consists of: percentage (%) of individuals from each replicate that have died, % that exhibit acute effects, % that exhibit color loss (bleaching) of different levels. From this, acute toxicological measurements were calculated, including LC50, AC50, and NOAEC. Measurements of growth following exposure were made in micrometers.

Methods:

Storage of sediment: -Temperature: 25 + 1°C -Light: Cool white at ~10 μmol photon m-2 s-1 - Photoperiod: 12 hr light- 12 hr dark -Chamber size: 500 ml widemouth jars with screw caps or petri dishes -Control culture medium: Seawater, salinity 35-37 psu, pH 8.2 - Experimental culture medium: NuSalts® Type 1, salinity 35-37 psu, pH 8.2 Specimen size: between 0.5-0.8 mm Experimental treatment: -Propylene glycol: 48-hr exposure to concentrations of: 2%, 4%, 6%, and 8% - 2-butoxyethanol: 48-hr exposure to concentrations of: 0.32%, 0.64%, 0.96%, 1.28%, and 1.44%

Error Analysis:

Statistical tests employed in analyzing data included analysis of variance (ANOVA), analysis of covariance (ANCOVA), Tukey’s Honestly Significant Difference test (HSD), and the Kolmogorov-Smirnov Goodness of Fit test. A significance level of 95% (p < 0.05) was used throughout.

Individual Files: