Quarterdeck 3.2
Responses to sublethal contaminant exposure
by Mahlon C. Kennicutt
You have heard of catastrophic environmental damage caused
by oil spills. What happens to the marine environment when an oil platform
becomes a long-term component of the local ecology? GOOMEX intends to find
out.
Many uncertainties surround the importance of environmental
disturbances caused by offshore oil and gas development and production.
The most significant unanswered questions involve chronic, low-level stresses
on ecosystems which result from discharges, spills, and leaks associated
with the long-term development of energy resources on the continental shelf.
A multidisciplinary team of researchers at Texas A&M University (TAMU) and
other institutions is conducting a three-phase program, called the Gulf
of Mexico Offshore Operations Monitoring Experiment (GOOMEX), to test and
evaluate a range of biological, biochemical, and chemical methods that may
indicate whether or not the local ecology around platforms is responding
to chronic, sublethal exposure to discharged pollutants.
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Kristie Willett, a graduate student in Veterinary Physiology and Pharmacology
at Texas A&M University, conducts experiments to determine how fish have
responded to exposure to organic contaminants associated with oil and gas
platforms in the Gulf of Mexico.
Offshore petroleum platforms are known to discharge a range
of materials over their lifetimes. These discharges can be associated with
activities such as drilling, ship operations, accidental spills, run-off
from the platform, discharge of produced waters, sand blasting, painting,
welding, and other practices. As a structure, a platform can also act as
a reef and produce a flux of materials to the seabed from biological organisms
attached to the platform and inhabiting the surrounding waters. As a result
of these various inputs our team of investigators expected that the presence
of a platform over a number of years would lead to a significant alteration
of the underlying seafloor and the organisms that live there. We also expected
that this change would directly or indirectly alter the local ecology.
Conditions around platforms result from the cumulative
long-term interaction between the platform structure, materials discharged
from the structure, and local oceanographic conditions. In the simplest
sense, the three-year Phase I of GOOMEX aimed to develop a detailed understanding
of whether or not conditions measured near a platform are significantly
different from those away from the platform, and whether or not these differences
could be attributed to the discharge of pollutants from the structure. Specifically,
the program was designed to test for toxic responses to contaminants, but
it also assessed alteration of seafloor sediment characteristics around
platforms. Disposal of coarse materials onto the surrounding sediments sets
the stage for a shift in marine-organism populations. Thus, aside from toxicity
caused by contaminants, we expected alteration of the seafloor (i.e., a
change in sediment grain size) and organic enrichment derived from marine
organisms living on the platform to exert significant additional controls
over biological patterns.
Changes in variables related to distance from the platform
can only be fully understood within the concepts of cause and effect and
biological significance. Any two places on the continental shelf can be
determined to be different if analyzed in sufficient detail. The GOOMEX
program is designed to provide circumstantial evidence of cause and effect
at several levels of biological organization as well as provide a foundation
for future studies of the processes through which the changes take place.
To increase confidence in our interpretations, we compared
the indications of ecological impact across several independent lines of
evidence and evaluated how well they agreed with one another. We also used
the concept of biological significance as a guiding principle. The goal
of monitoring is to detect resource degradation or environmental damage
and then provide guidance for prevention or reversal of undesirable impacts.
The relevance of specific effects must interpreted in the broader context
of the insults being sustained by marine resources in general.
The two most likely types of toxic contaminants associated
with platforms are petroleum hydrocarbons and metals (iron, lead, cadmium,
zinc, etc.). The distributions of each contaminant can serve as an indicator
of the potential for toxic effects. To implement Phase I of the program
our team of investigators analyzed metal and hydrocarbon contaminants in
bulk sediments, the water contained in them, and the tissues of marine organisms.
We also examined three different size ranges of bottom-dwelling marine invertebrates
(meio, macro, and megafauna) in terms of their community structure, life
histories and reproductive effort. Finally, we assessed the presence and
intensity of biochemical systems that protect animals from contaminants.
The program involved intensive sampling of the study sites (four sampling
events over 1 1/2 years) and state-of-the-art analytical techniques to produce
a comprehensive data set to test our hypotheses.
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Oceanography,
Texas A&M University
rshatto@ocean.tamu.edu
URL=http://oceanography.tamu.edu/Quarterdeck/QD3.2/Kennicutt/kennicutt.html
Updated September 13, 1995
