Marine Sponges ‘Sneeze’ to Expel Waste

A good sneeze can almost be life changing. The relatively violent reaction clears mucus, water, and contaminants with force, often making it easier to breathe.

Researchers have found that sponges also “sneeze” to unclog their internal filter systems of waste. Some of the oldest multicellular organisms in existence, sponges play a key role in moving nutrients around their aquatic ecosystem. Sneezing helps them open up the systems they use to grab nutrients from the water.

Before now, scientists often believed sponges got rid of waste through dedicated openings in their bodies.

“The big question was: Where is sponge waste excreted? Sponges filter a lot of water and produce a lot of wastes,” study author Sally Leys, a biology professor at the University of Alberta, Edmonton, tells Treehugger.

“Normally you'd think that wastes should be expelled out a large single opening (osculum) that the water is expelled from, but when [my co-authors] looked, they couldn't find much waste coming out the osculum.” 

To take a closer look, the researchers made time-lapse videos of the Caribbean tube sponge Aplysina archeri and Indo-Pacific species of the genus Chelonaplysilla. They filled the surface of the sponges in tanks and underwater.

“Then the image sequence could be played back faster so that a very long slow behavior became easy to see,” Leys says. “Particles could be traced on the images to follow where they go, and that showed that particles actually go very slowly and steadily against the normal feeding current, and they do this by being streamed along highways of near-invisible mucus.”

The videos show mucus accumulating on the surface of the sponge. Then, occasionally, the sponge will contract and push the waste-filled mucus off and into the water.

“Our data suggest that sneezing is an adaptation that sponges evolved to keep themselves clean,” says Jasper de Goeij, a marine biologist at the University of Amsterdam and the senior author of the paper, in a statement.

“Let’s be clear: sponges don’t sneeze like humans do. A sponge sneeze takes about half an hour to complete. But both sponge and human sneezes exist as a waste disposal mechanism.”

The findings were published in the journal Current Biology.

Although the expelled mucus is waste for sponges, surrounding fish often dine on the material that is sneezed away.

“We also observed fish and other animals feeding off of the sponge mucus as food,” says Niklas Kornder, the first author of the study and a doctoral researcher. “Some organic matter exists in the water surrounding the coral reef, but most of it is not concentrated enough for other animals to eat. Sponges transform this material into eatable mucus.”

It’s those kinds of abilities that make sponges so interesting for the research team.

“For me, I'm fascinated by how sponges coordinate behavior,” says Leys. “They have a lot of behavior—twitches, cringes, and full contractions—but no nervous system, and not really much of a muscular system either. How do they coordinate the behavior? Jasper's group is fascinated by how massive a role sponges play in redistributing food in the many habitats they live in.”

The study findings highlight sponges and their impact on the ecosystem. The amount of waste they expel is a critical food source for other animals.

“It highlights the importance of sponges in the ecosystem—transporting food (carbon/particles) from the water column to the ocean/lake floor where other animals can eat it,” Leys says.

“It's also wild that sponges a) can produce so much mucus, b) and move it so steadily along such beautiful mucus highways, and c) that the sponge knows when enough particulate waste has accumulated at a single point to then sneeze. And of course ... how does it coordinate that sneeze? Such cool findings and so many more questions.”