Endangered freshwater mussels spew water to help larvae survive

An endangered freshwater mussel spews water up to a meter away to give its hatchlings the best chance of survival, new research suggests.

The researchers were shocked to see the brainless creature’s behavior captured on film.

In spring, female Unio crassus mussels were seen moving toward the water’s edge and anchoring to the river bed, with their hind ends elevated above the waterline.

They then spewed out regular streams of water, which landed in the water up to a meter away. The blast cycles lasted from three to six hours.

These jets disturb the river surface and attract fish, and mussel larvae in the jets can attach to the fish’s gills and complete their metamorphosis into adults.

This jet has never been seen in any other mussel species, say the researchers from the University of Cambridge.

‘Who would have thought that a mussel, which doesn’t even have a head or brain, knows how to move towards the river bank and squirt water into the river during spring? It’s amazing,” said Professor David Aldridge of the university’s department of zoology, lead author of the report.

Unlike other mussel species, Unio crassus has a limited range of suitable host fish, including minnows and chubs.

According to the study, these species were attracted to the falling jets of water.

Researchers believe that mussels squirt water to increase the chances that their larvae will attach to suitable host fish.

Jetting in the air and not in the water means that the larvae are propelled greater distances from the parent mussel.

The study was carried out during the spring in the Biala Tarnowska River, Poland.

Samples of the water spouts of each mussel were collected for analysis, confirming that they contained viable mussel larvae.

Until now, there was only anecdotal evidence of this behavior, and some scientists thought that the jets of water might be a way for mussels to expel feces.

The researchers suggest that their findings may help explain why Unio crassus is an endangered species.

Leaving the water to squirt makes it vulnerable to flooding, destruction of river banks, and predators such as mink. And your need for specific host fish links your survival to theirs.

The research, published in the journal Ecology, was funded by the Woolf Fisher Trust.