CLOWN FISH NEED MORE ENERGY TO LIVE IN A BLEACHED HOME

If you’ve seen “Finding Nemo,” you’re familiar with the special relationship between clown fish and anemones, the stinging spaghetti rugs of the reef that Nemo calls home.

Normally, algae inside the anemone convert sunlight into energy to feed the anemone, which provides protection for the fish and its eggs. That’s why the clown fish chooses to live in the anemone.

But when warming temperatures or another environmental disturbance cause coral and anemones to bleach, the situation changes. Algae die. Anemones shrink. And clown fish, most of which remain in their bleached home, don’t reproduce like they used to.

Although a bleached anemone is deprived of algae, it’s still alive and may one day recover, said Tommy Norin, an ecological physiologist at the University of Glasgow in Scotland. There’s no reason the fish, which doesn’t even eat the algae, should be suffering. But it does.

To try to get a handle on this mystery, Norin and a team of collaborators looked at physiological indicators of stress in clown fish living around bleached anemones. Their work, published recently in Proceedings of the Royal Society B, suggests the higher cost of living in a stressful environment may partly explain these clown fish struggles.

Researchers collected 16 fish from a healthy coral reef near French Polynesia in the Pacific Ocean and took them back to the lab. They put half in tanks with healthy anemones, and half in tanks with anemones that had been bleached with hot water. The anemones were still living and had not yet shrunk, but their algal companions were gone.

After two weeks, the researchers moved the clown fish into tanks pumping out oxygen every few minutes and measured how much oxygen the fish consumed during their most sedentary times.

This gave them an idea of the fish’s basal metabolic rate — that is, how much energy the animals needed to sit around and do nothing.

The researchers found that the clown fish living with the bleached anemones had a higher basal metabolic rate than the fish living around healthy anemones. That is, the fish needed more energy to just stay alive around bleached anemones.

Suzanne C. Mills / New York Times Clown fish swim inside chambers used to measure their metabolic rate in the presence of bleached anemones. When warmer oceans bleach anemones, the clown fish that rely on them for shelter become very stressed out, scientists report.