It would be an understatement to say that mussels and other mollusks usually aren't thought of as being particularly active. Recently, however, scientists have documented a water-squirting behavior in just one species, which is apparently using the action to give its larvae a fighting chance.
For the study, a University of Cambridge team led by Prof. David Aldridge observed freshwater Unio crassus mussels in Poland's Biała Tarnowska River in the springtime. There were anecdotal reports of the mussels repeatedly squirting water from the banks of the river, but the phenomenon had never been scientifically documented – or understood.
The scientists did indeed witness female mussels moving to the river's edge, raising their back ends out of the water, then squirting water up to 1 meter (3.3 ft) out into the river. They would do so for three to six hours at a time.
Like other freshwater mussels, Unio crassus release their larvae into the water, where they latch onto the gills of passing fish. There, the larvae develop into juvenile mussels, at which point they drop off and settle on the riverbed.
In many cases, the larvae will only survive on certain types of fish … and this is particularly true of Unio crassus larvae.
With this challenge to survival in mind, the scientists surmised that the water-squirting behavior is intended to attract compatible fish – such as minnows and chub – and to deliver the larvae to them. Sure enough, when water-squirts collected from multiple mussels were analyzed, they were all found to contain viable mussel larvae.
"Who'd have thought that a mussel, that doesn't even have a head or a brain, knows to move to the river margin and squirt jets of water back into the river during springtime?" said Aldridge. "It’s amazing."
The unique behavior may also be at least part of the reason why Unio crassus is an endangered species. By moving to the river's edge, female mussels are more vulnerable to terrestrial predators such as mink, plus they may be stymied by flooding or destruction of the shoreline.
You can see one of the mussels in water-and-larvae-squirting action, in the following video. The research is described in a paper that was recently published in the journal Ecology.
Source: University of Cambridge