EMBARGOED FOR RELEASE UNTIL OCTOBER 11, 2006
Contact:
Christine Guilfoy
Office: (301) 634-7253
cguilfoy@the-aps.org
Rising Ocean Temperatures Have Oysters In
Hot Water
Temperature, pollutants attack oyster’s cellular power supply
Virginia Beach,
VA (October 11, 2006) – Oysters exposed to high water temperatures
and a common heavy metal are unable to obtain sufficient oxygen and convert
it to cellular energy, according to a new study presented at The American
Physiological Society conference, Comparative Physiology 2006.
The study showed how cadmium, a heavy metal, reduces
the oyster’s tolerance of warmer water temperatures and makes it more
vulnerable during the summer when water temperatures rise. Half of the
oysters exposed to the pollutant in 28° C (82° F) water died within 20 days,
said lead researcher Gisela Lannig. Oysters exposed to cadmium at lower
temperatures showed much lower mortality rate, suggesting that the
combination of high temperature and cadmium is more stressful than each of
these conditions alone, she said.
The study “Temperature tolerance in the oyster,
Crassostrea virginica, is affected by cadmium,” was carried out by
Lannig, of the Alfred Wegener Institute for Polar & Marine Research,
Bremerhaven, Germany, and Jason Flores and Inna Sokolova, of the University
of North Carolina at Charlotte. The work was done in North Carolina. The
researchers presented the study October 10 during a poster session at
Comparative Biology 2006: Integrating Diversity in Virginia Beach.
Oysters decimated
Oysters once thrived in the coastal regions of much of
the eastern United States, but over-fishing, global warming, rising ocean
water temperatures and increased pollution have combined to reduce the
oyster population to 5% of what it was 200 years ago, Sokolova said. The
loss of oysters has far-reaching environmental implications.
“We can’t even imagine the expanse of oyster reefs
100-200 years ago and their impact on the ecosystem,” Sokolova said. For
example, a century ago, the oyster population could completely filter the
water in the Chesapeake Bay in three days. Today, with the oyster population
continuing to decline from poor water quality and disease, it would take a
year to filter the same amount of water, she said. In addition to filtering
water, oysters create a kind of reef that other marine life depends upon.
“Studies have shown that there are more than 300
species reliant on oyster reefs, including at least 12 species important for
their commercial or recreational value, such as blue crabs, sheepshead,
croaker and stone crab,” Sokolova said. “Some of these species, such as blue
crabs, use oyster beds and reefs as nursery areas and as feeding grounds.”
The oyster beds are also important to a variety of marine life that serves
as food for larger fish. It was within this context that the North Carolina
team did their study.
Warm water increases
energy demand
The researchers divided oysters into three groups. One
group was acclimated to water that was 20˚ C (68˚F), one to 24˚C (75˚F) and
a final group to 28˚C (82˚F). All three temperatures are within the range
that oysters are exposed to in their natural environment, Lannig said. In
fact, this summer, which was unusually hot, water temperatures reached 32˚C,
she said. Each temperature group was subdivided into two subgroups, oysters
that were exposed to cadmium and those that were not.
The 20-day study found that oysters, as expected,
consumed more oxygen as the water temperature rose. Warmer temperatures
raise the oyster’s metabolic rate, which raises its oxygen and energy
requirements, Lannig explained.
In addition, oysters exposed to cadmium at 20˚C and
24˚C needed more oxygen than the oysters in their groups not exposed to
cadmium. That makes sense, because the pollutant places stress on the
oyster, which increases metabolism and oxygen demand.
Temperature plus cadmium =
power disruption
However, there was no difference in oxygen consumption
between the two groups acclimated to 28˚C. The researchers concluded that
the cadmium-exposed oysters in this group needed more oxygen than the
unexposed group, but were either unable to obtain enough oxygen, convert the
oxygen they obtained to energy, or both. The researchers drew this
conclusion, Lannig said, based on measurements of respiratory activity, the
animal’s blood oxygen content and mitochondrial function.
The 28˚C cadmium-exposed group spent more time in
respiratory activity, trying to take in oxygen. Their shells were open
significantly longer than any of the other groups, a measure of the amount
of time they spend “breathing.” (When oysters open their shells, they are
taking in oxygen. Oxygen flow stops when they close the shell.)
The researchers also examined the effect of cadmium and
temperature on the mitochondria of the oyster’s cells. The mitochondria are
the cell’s power plant, producing energy for the oyster, including for
ventilation and circulation.
“We found that mitochondria are very sensitive to
cadmium at high temperatures,” Lannig noted, suggesting that the higher
temperature and cadmium exposure negatively affect the mitochondria’s
ability to produce energy.
Blood oxygen falls
In a second experiment, the researchers acclimated two
groups of oysters to 20˚C water. One group was exposed to cadmium. Both
groups were then subjected to an acute temperature increase of 4˚C overnight
(to 24˚C).
“Here we saw that the cadmium-exposed oysters showed a
decrease in blood oxygen content with the higher temperature, but not the
control group that was not exposed to cadmium,” Lannig said. Once again,
this shows that the combination of temperature and pollution combine to
intensify the stress placed on the oyster’s physiological system.
In future experiments, the researchers will try to
determine whether the combination of temperature and pollution is preventing
oysters from obtaining enough oxygen or whether it is interfering with the
animal’s ability to use the oxygen it obtains, Lannig said. These
experiments on oyster physiology could be important to save what is left of
this ecologically important population.
* * *
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