Video: This time-lapse video reveals the “sneeze behavior” of an Indo-Pacific sponge. © Current Biology/Kornder et al.
“Hatschi”: When we sneeze, we clean our respiratory system by bursting out droplets of mucus. A similar process is also used by one of the simplest and oldest animals, according to a study: time-lapse recordings show that sponges release slime laden with dirt particles into the surrounding water through periodic surface contractions. This concept is thus possibly one of the oldest methods used by organisms to get rid of unwanted substances.
They have existed since primeval times and to this day thousands of species inhabit many different aquatic habitats on earth: The sponges are considered to be one of the simplest and most primitive forms of multicellular creatures with specialized tissues. Through their literally spongy bodies, they filter organic particles from the water, which they use as food. To do this, they suck the liquid through small pores (ostia) into an internal canal system in which specialized cells absorb food particles and create a flow by beating small flagella. The water then leaves the sponge body again through the so-called oscula. The sponge also gets rid of waste products such as leftover food via these outflow openings and the water flow.
Sponge behavior in time lapse
Until now it has been assumed that disposal via the outflow openings is also supported by fine contractions which have been observed in sponges. This behavior has already been referred to as a “sneeze”. However, the current study now shows that the contractions are even more similar to a sneeze than previously thought. Apparently, the sponges use mucus to rid themselves of useless dirt particles that could clog their filter system. This emerges from studies carried out by the team led by Jasper de Goeij from the University of Amsterdam on sponges in aquariums and in reefs. Their cameras focused on specimens of the Caribbean sponge species Aplysina archeri and an Indo-Pacific species from the genus Chelonaplysilla.
As the team reports, the time lapse in the video recordings makes it clear: slime, which is obviously laden with dirt particles, emerges from the seawater entry pores (ostia) against the flow direction. This substance is then transported away and accumulates in certain places on the sponge’s surface in the form of crumbs. These are then released into the surrounding water by the periodic contractions previously described as “sneezing”. In other words, it looks like the sponges are constantly ejecting slimy particles to get rid of dirt-substances.
“Our results suggest that this is an adaptation that sponges have evolved to keep themselves clean,” says de Goeij. When comparing it to its human counterpart, however, one aspect needs to be emphasized: sponges don’t really sneeze suddenly: “The process takes about half an hour. But both the sneezing of sponges and the sneezing of people are used for purification,” says the marine biologist.
Sponges sneeze food for fish and co
The researchers assume that the sneezing behavior is typical of sponges in general. “I’ve seen slime accumulating on different sponges while diving and in pictures taken by other scientists for other purposes,” says lead author Niklas Kornder from the University of Amsterdam. However, one aspect of the “sneezing” of the sponges remains particularly mysterious, say the researchers. “In the videos, you can see that the slime moves along specific paths on the surface of the sponge before it accumulates,” says Kornder. According to him, it is not yet clear how this promotion mechanism works. “Further analysis is needed to uncover this,” says Kornder.
Finally, the scientists draw attention to another interesting aspect: Apparently, the sponges provide food by sneezing in the sea: “We have observed that fish and other animals ingest the sponge mucus as food,” says Kornder. “Some organic matter is present in the water surrounding the coral reef, but most of it is not concentrated enough for other animals to ingest. Sponges apparently turn this material into edible slime,” says the researcher.
Source: Cell press, technical article: Current Biology, doi: 10.1016/j.cub.2022.07.017