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Oysters under siege: Heat and pollution

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11:12am, April 27, 2005
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Many aquatic species become stressed when water temperature rises. Such species are even more vulnerable to thermal stress when their environment is polluted, a pair of ecotoxicologists finds.

Gisela Lannig and Inna Sokolova of the University of North Carolina in Charlotte incubated coastal oysters for 40 days at one of three temperatures: 20°C (68°F), a warm but tolerable temperature for the creatures, at 24°C, or at 28°C. The rate of oxygen use, which can be an indicator of physical stress, was three times as high in oysters kept at the warmest temperature as it was in those kept at the coolest.

Adding 20 micrograms per liter of the toxic heavy metal cadmium to the oysters' water made matters worse, with oxygen consumption jumping 66 percent and 200 percent in oysters at 20°C and 24°C. For oysters in 28°C water, the cadmium didn't increase oxygen use, which Lannig initially found perplexing.

Further probing indicated that the animals in the warmest water were already running full tilt and couldn't take in any more oxygen. Within 3 weeks of beginning cadmium exposure, half of these oysters were dead, compared with just 6 percent of those at 24°C and none in the 20°C water, Lannig reported at the Experimental Biology meeting in San Diego in early April.

Cadmium thwarts an enzyme required for energy production by the mitochondria within cells, Lannig found. So, in warmer cadmium-polluted environments, "the animals needed more energy but their mitochondria were increasingly unable to produce it," she says.

This suggests, says Lannig, "that with global warming, some areas that are polluted might become a kind of graveyard for these animals."

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