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Sponges Feel the Heat From Climate Change

Jessica Marshall, Discovery News

"The tissue got necrotic and the skeleton could be seen coming out of the tissue," she added.

Moreover, one of the symbiotic microbes Webster monitored totally disappeared from the sponge within the first 34 hours at 33 degrees. When Webster analyzed the microbial population overall, she found no change until 33 degrees, at which point the normal microbes were lost, while populations of pathogenic bacteria associated with coral bleaching and coral disease increased.

"We aren't really sure whether the sponge stress was causing the symbiont [the microbes] to disappear or whether the sponge was losing the symbiont and that was causing the stress," she added. "At this point we don't really have a handle on which came first."

Thirty-three degrees Celsius is a temperature that is occasionally reached today in isolated pockets of the Great Barrier Reef. "With the temperature increases that are predicted, we will see it more frequently," Webster noted.

Intriguingly, 33 degrees is the same temperature threshold at which coral bleaching is observed.

"I guess the implications of that are, as we see temperature elevations, we're going to start seeing some breakdowns in microbial relationships with marine organisms," she said. "Microbes are a relatively unstudied group, yet they have a really important role for the function of many marine systems."

Russell Hill, a marine microbiologist at the University of Maryland Biotechnology Institute in Baltimore, agrees. His recent results suggest that microorganisms associated with sponges may help to convert nitrogen into a form that sponges and other organisms can use.

It's still highly speculative, Hill said, but the combined findings suggest that if the microbes experience stress at elevated temperatures, "that could affect the entire nitrogen cycle of the reef ecosystem."

"The big take-home message is how important it is to do more research on the microorganisms in the whole reef ecosystem," he added. "Probably the key to good functioning of these reef ecosystems lies in the microbes."

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