Contractors complaining of a disappearing subsea market in recent years, please spare a thought for German research institutions who have just noticed that an expensive underwater observatory has simply vanished.

The Boknis Eck Observatory that was installed on the seabed at the exit of Eckernforde Bay in the Baltic Sea off Kiel in December 2016 has been missing since 21 August.

The two large structures are used to collect data on things like water temperature, salinity and oxygen levels and together weigh some 770 kilograms.

German research company Geomar, which is behind the project, said the structures were “removed with great force from their position”, but their current whereabouts are unknown.

A dive team in late August found only the torn cable to shore at the site, which is situated within a restricted marine area.

“At first we thought it was a transmission error,” said Boknis Eck co-ordinator Hermann Bange after the observatory stopped transmitting data on the evening of 21 August.

"When the divers reached the bottom of the sea … at the observatory's location, they found only the torn off land cable. It was completely shredded,” he added.

As the subsea structures are so large and heavy, Geomar has ruled out currents, storms or marine animals as culprits.

“We tried to find the devices with our own research and other diving applications, so far without success. That's why we would be very happy about any hints,” Bange said, asking for help to locate the items, which together cost around €300,00 ($331,000).

“The data that we collect is downright priceless,” he added.

“Maybe someone saw something on the morning of 21 August at the Sperrgebiet Hausgarten near the Hokholz campsite, or someone has found parts of the frames somewhere on the beach,” he added, hoping the general public can help solve the subsea mystery.

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Germany probes vanishing subsea kit mystery