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Ballast testing is the first step: the team place the SPIRULA vehicle in shallow water, adjusting its position and buoyancy by adding or removing weight. “It’s important that the vehicle lies horizontally in the water and that it’s slightly buoyant,” says project leader Ralf Bachmayer (front).

SPIRULA takes a successful dive in the Aegean Sea

In May, the deep-sea monitoring system SPIRULA embarked on its inaugural expedition in ocean waters. The test off the Greek island of Milos in the Aegean Sea was an all-round success, to the great satisfaction of MARUM Professor Ralf Bachmayer and his research group.

27 May 2025 is a big day for the research group led by Professor Ralf Bachmayer from the Innovation Center for Deep-Sea Environmental Monitoring in Bremen. The interdisciplinary team of six have arrived on the Greek island of Milos, in the Aegean Sea, with SPIRULA in tow. SPIRULA, which stands for “SPiraling Intelligent Robotic Underwater monitoring pLAtform”, is the deep-sea monitoring system the team have been developing over the past several years. The monitoring system is now ready for testing in a real-world setting.

Team and technology alike have a long journey behind them: they started out at MARUM – Center for Marine Environmental Sciences at the University of Bremen, and continued on through Germany and several other countries before reaching the Port of Piraeus, where they boarded a ferry to the volcanic island of Milos.

Deceptive calm: at the SPIRULA testing site off Paliochori Beach, the springtime winds are strong. And at a depth of six to eight kilometres below Milos—one of the volcanic islands in the South Aegean Volcanic Arc—a magma chamber continues to exhibit strong hydrothermal activity.
Five hundred meters from Paliochori Beach, the SPIRULA team are renting space for their “base camp”.
The team have an open-air workshop for assembling the SPIRULA system and controlling the electronics embedded in the underwater vessel. Here, software engineer Monja Daub—responsible for sensor data processing and electronics, and part of Bachmayer’s team since the start of 2025—and postdoc Christian Meurer check that all signals are going through as desired. While they work at the base camp, their colleagues are building the platform that will transport the SPIRULA system out to sea and seeking a suitable launching site at the bay.
The interior of the SPIRULA vehicle contains many electronic parts that were developed in-house—including the main processor for steering the vehicle.
The small round knob seen at the front is the hydrophone: a device that sends and receives acoustic signals, supporting communication and navigation.
After two days of preparation and controls, the entire SPIRULA system is brought to the shore and assembled for its first dive. The electronic components are placed in waterproof, pressure-resistant cylindrical containers. One of the system’s three cameras can be spotted in the glass dome to the right. The researchers and technicians are a dream team: (from right to left) software engineer Ankita Jadhav, systems engineering student Jan Gümpel, mechatronics engineer Árni Thor Thorgeirsson and postdoc Christian Meurer. Not pictured are project leader Ralf Bachmayer and software and mechatronics specialist Monja Daub.
The functionality of the sensors and sonar on the SPIRULA vehicle must first be tested in the water. The team adjust and control ballast and the propulsion systems.
Converting a water-tight transport box into a make-shift desk for the laptop used to steer the SPIRULA vessel via a wireless network connection: (from left to right) Ankita Jadhav, Jan Gümpel, Monja Daub and Christian Meurer.
All manner of wires and ropes on the platform to untangle: Monja Daub installing the network and antenna cables.
Árni Thor Thorgeirsson assembles the lander component of the SPIRULA system, attaching weights to ensure the device remains on the ocean floor. Vehicle and lander are connected via a fibre optic cable.
At the University of Bremen, postdoc Christian Meurer studies robust monitoring systems like SPIRULA. The aim is to develop devices capable of detecting seeps in CO2 capture and storage locations on the ocean floor. CO2 sequestration in the seabed is a widely discussed solution for mitigating climate change; for the method to be viable, however, it’s critical that storage sites for the greenhouse gas are monitored closely to detect gas seeps and identify impacts on the local ecosystem.
All systems go: The SPIRULA lander is suspended from the frame, and the vehicle is sitting at the front of the platform designed and constructed by systems engineering student Jan Gümpel. Because the in-house development proves to be extremely practical and versatile, the crew dub it “Busy Beaver”. The SPIRULA system is lowered into the water through the opening in Busy Beaver’s floor.
And then, all hands on deck: pushing Busy Beaver and its precious cargo into the water.
Ralf Bachmayer and Monja Daub use an inflatable boat to tow Busy Beaver out to the open sea.
Anchoring Busy Beaver at an “interesting” location.
The location is “interesting” due to the presence of an underwater bacterial mat, which is indicated by the water’s lighter appearance at the surface. Bacterial mats arise where hydrothermal activity is present: gases like sulphur escape from the ocean floor and are used by certain kinds of bacteria for chemosynthesis. Detecting gas seeps is one of the key applications for the SPIRULA system.
Lights and action: the SPIRULA vehicle begins to glide above the ocean floor. The camera in the glass dome photographs the underwater environment, while the camera mounted in the vehicle’s “underbelly” takes pictures of the seabed. The four sensors at the front measure the water’s conductivity, temperature, pressure and turbidity. A multi-beam sonar is used to characterise and classify the ocean floor.
The high-resolution images taken by the camera installed in the underside of the SPIRULA vehicle are transmitted to the laptop onshore. This setup enables the researchers to observe the expedition in real time—and to correct course if necessary. All visual and acoustic data are also recorded in the vehicle itself. Project leader Ralf Bachmayer is highly satisfied with the outcome: “The most important parts functioned well.”
After a long day, the team once again guide the SPIRULA system to dry land. They’ll soon be enjoying their dinner at the local tavern. Dessert is a breath-taking sunset.
The happy team after the successful tests: (from left to right) Árni Thor Thorgeirsson, Monja Daub, Ankita Jadhav, Christian Meurer, Ralf Bachmayer, Solveig Bühring, Jan Gümpel.
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