The gentle glow of moonlight on water has moved musicians, poets and painters – and, it turns out, molluscs. Researchers have discovered the opening and shutting of oysters’ shells appears to be tied to the lunar cycle.

Biological clocks have intrigued scientists for centuries, and researchers in the field won the 2017 Nobel prize for studies into the 24-hour body clock.

However, organisms do not necessarily have biological processes linked only to the rhythm of day and night, the circadian clock. Other patterns that include links to the tides have been found for species including the horseshoe crab, and to the phases of the moon for creatures including the bristle worm. Some have suggested the latter may also affect humans.

Now experts say they have found evidence that oysters not only have a circadian clock and a tidal clock, but are also attuned to lunar rhythms.

“It was a surprise to see that there is a such an effect of the moonlight,” said Laura Payton, co-author of the research from the University of Oldenburg.

Writing in the Biology Letters journal, Payton and her colleague Damien Tran from the University of Bordeaux describe how they tracked the behaviour of 12 Pacific oysters submerged off the French coast over the course of three and a half lunar cycles from the end of 2014.

The team used electrodes to track the molluscs’ degree of opening every 1.6 seconds and looked at astronomical data to assess how much of the moon was illuminated.

The results reveal the oysters were most open in the buildup to – and presence of – a new moon, and less open as the moon entered first quarter and full phases.

The team says that suggests oysters can sense moonlight – even though it is far less intense than the sun’s rays.

However, Payton said the situation was complex, noting the creatures appeared to be able to tell if the moon was waxing or waning: the oysters were generally more open during the third quarter than the first quarter.

Payton said one possiblity was that the benthic bivalves may have evolved an internal lunar clock, rather than passively relying on direct cues. In that case, she added, the moonlight sensed by the oyster would help keep this clock in sync with the environment rather than directly triggering the opening and shutting of the shell – similar to how humans use daylight to keep their internal 24-hour clock on track.

The team suggests the increased opening of the oysters when moonlight levels are lower might be linked to the possibility that more food is available at low light levels: previous studies have suggested the movement of plankton also appears to be influenced by light. “We know that oysters open their valves when there is food,” Payton said.

However, the study did not look at the impact of the moon on oysters’ behaviour in all seasons, or take into account cloud cover – and hence the actual level of moonlight the molluscs experienced.

David Wilcockson, a senior lecturer in aquatic biology at Aberystwyth University, said there were still many mysteries in the field. “We know that, for example, tidal, lunar and circadian clocks appear to have separate mechanisms, but they are to some extent linked – and we don’t know quite how and to what level,” he said.

Wilcockson said human activity could cause unexpected problems in marine environments – an issue research like the latest study could help examine. “If you have coastal lighting, for example, or lighting on marine structures, then of course we don’t really know what the impacts of those might be,” he said.