Sponges Feel the Heat From Climate Change

Aug. 28, 2008 -- In the oceans, it's not just corals that feel the heat from climate change.

New research finds that marine sponges suffer at the same elevated water temperatures that cause corals to bleach, suggesting that coral reef ecosystems may experience broad effects in a warming ocean.

Coral bleaching is a well-known phenomenon predicted to occur in warming oceans. It happens when the single-celled algae living within the corals disappear, leaving only the white coral skeleton behind.

Because of the symbiotic relationship between the algae and the coral -- the algae provides up to 90 percent of the coral's food -- the corals die when the algae leave.

But Nicole Webster of the Australian Institute of Marine Science in Townsville noted that corals are not the only marine creatures that rely on a symbiotic relationship with microorganisms to survive.

Microorganisms can make up as much as 40 to 60 percent of the weight of some sea sponges. Meanwhile, clams, nematode worms and even starfish can have bacteria or other microbes living on or in them, although not enough research has been done in many cases to know whether the relationship is truly a "you-scratch-my-back-I'll-scratch-yours" symbiotic association.

Webster tested samples of a common sponge from the Great Barrier Reef, Rhopaloeides odorabile, a brown, velvety sponge that can range from fist-sized to the size of a large beach ball -- and whose name derives from the observation that out of the water it smells like bile. "It's a very stinky sponge," Webster said.

She placed pieces of the sponge in water of different temperatures and observed the effect on the sponge and the microorganisms over about a month.

"The health of the sponge was unaffected at 27, 29 and 31 degrees Celsius [81, 84, and 88 degrees Fahrenheit]," Webster told Discovery News. "But at 33 degrees [91 degrees F], within only three days we saw signs of stress."