Biology Faculty Proceedings, Presentations, Speeches, Lectures

Tissue analysis of the oyster Crassostrea virginica after the Deepwater Horizon oil spill

Event Name/Location

American Geophysical Union (AGU) Fall Meeting, 2013

Presentation Date

1-1-2013

Document Type

Conference Proceeding

Description

The Deepwater Horizon accident (DWH) of April 20th, 2010, in the Gulf of Mexico (GoM) released crude oil into the ocean column for 4 months. An estimated 685,000 tons of crude oil was released, making DWH spill the largest accidental spill in maritime history. The immediate impacts of the spill were evident, including oil slicks, fouled beaches and fouled, often dead wildlife. Longer-term impacts are less understood, and reliance on studies of past spills, e.g. Exxon Valdez, may not be applicable given the substantially greater magnitude of DWH (Valdez spilled 37,000 tons) and different environmental settings (predominantly rocky shorelines vs. saltmarsh-dominated coastlines). Many molluscan species exhibit responses to oil spills or other hydrocarbon contamination. Bivalved molluscs are commonly used as bioindicator organisms in part because they concentrate both metals and organic contaminants in their soft tissues. We used the American oyster Crassostrea virginica to measure exposure to and impact of the spill as the abnormal transformation of soft-tissues, or metaplasia. Metaplasia is the reversible transformation of one cell type into another. Molluscan metaplasia has been associated with exposure to petroleum contamination. While oyster epithelium is normally stratified columnar and ciliated, experimental exposures often result in metaplasia of gill, digestive and renal tissues. The occurrence and frequency of metaplasia may also be an indication of the longevity of a spill's impact. For example, individuals of the mussel Mytilus trossulus in Prince William Sound continued to exhibit metaplasia of the digestive gland more than 5 years after the Exxon Valdez spill, with an occurrence directly related to concentrations of PAHs in the animals. We focused on the hypothesis that DWH spill exposure resulted in metaplasia of gill and digestive epithelial tissues, both during and after the spill. Those transformations are eventually reversible, although on an unknown timescale. Specimens examined included: (1) Six individuals from Dauphin Island, Alabama and 7 from Apalachicola Bay, Florida during and after the spill in 2010; and (2) three individuals collected outside of the GoM, from Chesapeake Bay in 2013. All Chesapeake Bay specimens displayed normal, columnar, ciliated gill and digestive epithelia. Four Dauphin Island specimens displayed unciliated, stratified epithelia and vacuolated, atrophied digestive tracts. All Apalachicola Bay specimens presented similar metaplasia. Given the expectation of ciliated tissues, these results suggest a significant frequency of metaplasia in GoM specimens (Fisher's exact test, p=0.0179). The results are preliminary, however, and are being tested with increased sample sizes of control and exposed specimens, as well as GoM specimens collected in years 2011-2013.

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