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Aug 11, 2022
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Sponges “sneeze” to get rid of unwanted waste

Sponges "sneeze" to get rid of unwanted waste

Sponges are ancient filter-eating animals that rely on maintaining the flow of water through their body for suspended food and dissolved oxygen. They do not have a nervous, digestive or circulatory system, and they remove waste products by throwing them into the same stream of water. However, a new study that analyzed videos of sponges over long periods of time has revealed a specific technique they use to get rid of waste material inside their bodies.

As one of the oldest multicellular organisms, the sponge spends most of its life stuck to the substrate and is unable to budge when conditions get nasty. Under such conditions, it can absorb unwanted sediment particles along with a constant influx of water. These particles will soon clog the sponge’s filtration system, so they must be removed. And the sponge does this by a long contraction called a “sneeze.”

“Our data suggests that sneezing is an adaptation that sponges have evolved to keep themselves clean,” said Jasper de Gooy, a marine biologist at the University of Amsterdam, who led the study.

Although biologists knew about the behavior of sponges when contracting, the authors of this paper show that when they sneeze, they get rid of materials that sponges cannot use. “Let’s be clear: Sponges don’t sneeze the way humans do. It takes about half an hour to sneeze a sponge. But both a sponge and a person sneeze as a waste disposal mechanism,” de Gooy says.

The researchers used time-lapse videos of sponges to show that these organisms don’t just get rid of waste and unwanted particles in the water that flows out through the excretory pores. They actively secrete mucus, often against the direction of water flow, onto their outer surface. They then expel the unwanted particles through their pores and they coalesce into viscous mucus clumps. From time to time, the sponge experiences a contraction (sneeze), which loosens the mucus strands and accumulated particles, throwing them into the water column.

What is a waste for a sponge is a godsend for a fish. The fish hang around the sponges, waiting for these strands of slime to be shed so they can eat them.

“We also observed how fish and other animals fed on the mucus of sponges,” explained the first author of the study, Niklas Korder. “There is some organic matter in the water surrounding a coral reef, but most of it is not concentrated enough for other animals to feed on. Sponges turn this material into edible slime.”

The researchers noted this “sneezing” behavior in two species of sponges – the Caribbean tubular sponge Aplysina archeri and another Indo-Pacific species from the genus Chelonaplysilla.

“In fact, we believe that most, if not all, sponges sneeze. I have seen mucus build up on various sponges during dives and in photographs taken by other scientists for other purposes,” said Korder.

“Our findings open up possibilities for a better understanding of the cycling of matter in some of the most ancient metazoans,” the authors write.

Many aspects of sponge “sneezing” have yet to be explored. “You can see in the video that the mucus travels in certain paths on the surface of the sponge before it accumulates. I have a few hypotheses, but more analysis is needed to figure out what’s going on,” Korder says.

“Many scientists consider sponges to be very simple organisms, but what we are most often amazed at is the flexibility they exhibit to adapt to their environment,” de Goy said.

The study is published in the journal Current Biology.

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