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(Click to enlarge) Oysters C. virginica from Louisiana. (Photo credit: Phil DeVries)
Separate groups of scientists studying the Deepwater Horizon
oil spill impacts on oysters along the Gulf coast recently published
their findings in two journals: the November 2012 issue of Environmental Science and Technology: Assimilation of oil-derived elements by oysters due to the Deepwater Horizon oil spill; and the December 2011 issue of Journal of Shellfish Research: Chemical and physiological measures on oysters Crassostrea virginica from oil-exposed sites in Louisiana.
Drs. Ruth Carmichael and Thomas Soniat led studies using the eastern oyster,
Crassostrea virginica,
as an indicator for potential oil spill effects on local food webs
along Louisiana, Mississippi, and Alabama coasts. Oysters are a species
of choice for ecosystem studies because they are economically and
ecologically valuable to the Gulf region and because their tissue and
shell act like powerful recorders of their environment.
The Soniat team looked for biological responses, such as increased
susceptibility to disease and reduced reproductive capability, to
hydrocarbon contaminants in oyster tissue. Researchers recorded oyster
health, sex, and gonadal condition; analyzed tissue for polycyclic
aromatic hydrocarbons (PAHs); and measured environmental conditions of
temperature, salinity, and oxygen. The Carmichael team looked for
consumption of oil-derived organic material, including six trace
elements most likely to
(Click to enlarge) Oysters collected at one of the sampling sites off the Louisiana coast. (Photo credit: Thomas Soniat)
indicate exposure to oil hydrocarbons, in new shell growth of oysters
as well as in their tissue. Researchers analyzed stable isotopes in
oysters and in suspended particulate matter available as food and
compared them with weathered and fresh oil. Neither study found evidence
of oil-related contamination at levels above prior background or
pre-spill conditions. Soniat’s results found that PAH levels,
environmental conditions and reproductive capacity in oyster samples
were similar in oiled and unoiled areas six months after the capping of
the wellhead. Carmichael’s results found that oil-derived elements did
not have a statistically significant influence on the stable isotope
composition of oyster samples.
Soniat cautioned that his group’s results not be over applied because
of the study’s spatial and temporal limitations. Carmichael suggested
that her group’s findings have alternate possibilities including the
oysters not consuming oil materials during their period of study or
oyster samples consuming too little to detect. Both studies point to
complexities in interpreting and isolating potential effects of the
Deepwater Horizon oil spill.
(Click to enlarge) Oyster sampling sites along the Gulf coast for studies led by Dr. Thomas Soniat and by Dr. Ruth Carmichael.
The study authors are:
Ruth H. Carmichael, Amanda L. Jones, Heather K. Patterson, William C.
Walton, Alberto Perez-Huerta, Edward B. Overton, Meghan Dailey, and
Kristine L. Willett (
Environmental Science & Technology 2012
46 (23), 12787-12795); and Thomas. M. Soniat, Matthew A. Tarr, and Megan A. Thorne (
Journal of Shellfish Research 2011
30, (3) 713-717).
This research was made possible in part by Grants from BP/The Gulf of Mexico Research Initiative (GoMRI) through the
Alabama Marine Environmental Science Consortium and the
Northern Gulf Institute . The
GoMRI
is a 10-year, $500 million independent research program established by
an agreement between BP and the Gulf of Mexico Alliance to study the
effects of the
Deepwater Horizon incident and the potential associated impact of this and similar incidents on the environment and public health.