Oysters exposed to heated water and a common heavy metal are unable to obtain enough oxygen to fuel bodily processes, a new study shows.

Scientists found that when they exposed oysters to high temperatures and to cadmium, half of the oysters died within 20 days.

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Oysters exposed to cadmium at lower temperatures showed a much lower mortality rate, suggesting the combination of the two conditions is more stressful than either temperature or the metal alone.

The results suggest that as temperatures rise due to global warming, and coastal pollution increases, the outlook for oyster survival is grim, the scientists said here this week at a meeting of the American Physiological Society.

Double whammy

The researchers acclimated oysters to one of three water temperatures, all within the range of their natural environment: 68 degrees Fahrenheit, 75 degrees and 82 degrees.

For each group, the researchers exposed half of the oysters to cadmium.

Oysters can't regulate their body temperature as mammals can, so as the ocean temperature increases, the shelled sea creatures heat up.

As expected, the oysters in warmer water ramped up their respiratory and heart rates, similar to what happens when a person exercises.

All three groups exposed to cadmium required more oxygen than those not exposed to the metal.

The cadmium-exposed oysters in the 82-degree water were unable to get sufficient oxygen, but not for lack of trying.

These oysters spent more time with their shells in an open position than any of the other oysters, a measure of time spent "breathing."

When oysters open their shells, they are taking in oxygen from the water; when they close them, oxygen flow is cut off.

"They were gasping," said lead researcher Gisela Lannig of the Alfred Wegener Institute for Polar & Marine Research in Bremerhaven, Germany.

Power outage

The researchers also found mitochondrial damage in the oysters that were exposed to a combination of cadmium and the warmest water.

Mitochondria are an animal cell's power plants, producing energy needed for ventilation and circulation.

The results showed no mitochondrial damage in oysters living in the high-temperature water without cadmium or the lower-temperature water containing cadmium.

So the increased need for oxygen, coupled with cell damage, led to the gasping oysters, the scientists concluded.

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