The story of the crab and the seismometer on the ocean floor

A spider crab decided that the seismometer dropped by scientists would be its home, and that's when the battle begins.

Thompson is a scientific research ship floating in the middle of the ocean. But on this ship, you will very rarely hear the sounds of the sea. Because most of the time, you will be surrounded by the noise of the engine, the exhaust blower and the climate control system, or the sound of the winch.

And on this ship hundreds of kilometers from the mainland, scientific activities never stopped. 24 hours a day, everyone will be constantly working to prepare, deploy and restore geological sensors on the ocean floor. They are trying to understand the complex questions of what makes the volcano active - specifically, Seamount Axial, about 400 kilometers west of Cannon Beach, Oregon.

But it was also on this seemingly boring journey that the researchers aboard the Thompson had the opportunity to witness a drama under the ocean waves. It's the story of man versus nature, in a battle of attrition, atop the Pacific Northwest's most active volcano.

It's a story that you might call "The battle between spider crabs and seismometers".

The spider crab wants to make a nest in the seismometer.

One day in late June, researchers were operating an ROV - a remotely operated vehicle - called the Jason moving along the ocean floor. The machine has titanium arms with "fingers" that make it possible to pick up things on the seabed, move sensors, even play the violin if it gets the chance. To put it simply, it's a pretty impressive and flexible robotic arm.

'It looks easy, but it's actually very difficult. You must move the vehicle moderately. Then use the arm to do really sophisticated tasks," said Oregon State University volcanologist Bill Chadwick, the ship's chief scientist.

ROV Jason and its arms are controlled by a technician, who will sit in a control room housed inside a container on deck. People jokingly call this space a 'truck'. A dark and cold car. Video feeds from Jason's camera covered one wall in the room. They show parts of the ocean floor as Jason glides through them - lava flows, pillars, cliffs, hydrothermal vents - some of which have never been seen before by humans.

That day, the team had just dropped off a specialized seismometer, which is designed to learn what looks like the shape of a magma chamber under a crater. Engineer Ted Koczynski says the seismometer is very sensitive to vibrations, and they needed a car-sized plastic dome above it to protect it.

Koczynski was not on the ship, but worked at the Lamont-Doherty Earth Observatory in New York. "The whole idea of ​​the shield's job is to stop any flow coming in and affecting the seismometer," he said.

Jason's job is to lift the dome from the seabed with its titanium claws and drop it above the seismometer. A group of researchers sat in the truck behind the control technician to watch Jason at work.

When the ROV was just about to put the dome on top of the device, everyone saw it.

Expedition leader Akel Kevis-Stirling prepares to deploy Jason's remote-controlled vehicle to explore the Axial Seamount, an undersea volcano about 400 kilometers off the Oregon coast.

While Jason's back was turned, a large orange spider crab - with a body size about two meters long - entered the device and took its place at the top of the seismometer.

'I didn't include the crab in my plan,' perplexed Bill Chadwick, because he knew this would be a problem.

A seismometer is designed to be sensitive enough to respond to a slight electrical current, so it would certainly be sensitive enough to sense the pats of the crab's tiny paws.

After some strategic discussions, a campaign to attack and deal with the crab began.

Since the crab was so far inside the sensor housing, people were worried that Jason's claws might damage the devices. So they decided to try Jason's vacuum tube, something called "Slurp".

Jason's control technician, Tito Collasius, was excited by this challenging and never-before-seen mission. He manipulated the machine's claws to remove the vacuum nozzle. 'Here's the one for you,' he said as he moved it toward the crab.

'We're coming. This is the final warning,' added Chadwick, standing beside Collasius.

But the crab saw, or somehow sensed, the impending doom. And it started to go away.

Then, seemingly wanting to prove his bravery, the spider crab stopped.

'His name will be Moriarty,' said Collasius, calling the crab after the villain in the Sherlock Holmes series.

It is at this point that the war between the claws begins. And in a battle between the titanium "crabs" and the spider crab's claws, Jason had the advantage. A cheer erupted inside the truck as the titanium claws gripped and slowly pulled the crab out.

'They eventually grabbed it by the foot and carried it away. It was funny,' recalls Kelly Chadwick, a data logger on duty at the time.

The technician controlling Jason carried the crab about 20 meters away from the gauge and then dropped it. The crab immediately dashed away and disappeared.

ROV Jason pulls the spider crab from its hiding place on top of the seismometer.

The story of the spider crab and the seismometer spread throughout the ship and delighted everyone. Obviously, when you are stuck on a boat in the middle of the ocean, this is the most entertaining entertainment.

That seemed like a happy ending to the story. But as time went on, suspicious things began to happen beneath the waves.

First, one of Jason's thrusters popped open, leaving it only able to move horizontally on the ocean floor. This left Chadwick speculative and worried.

'We were forced to remove the crab from one of our tools. And now, one of Jason's thrusters failed, so now he's moving around like a crab. I think the crabs have 1 more point, 1-1, the score is even," he said.

But the balanced score did not hold for long. When the scientists were pulling up the seismometer and the shield to check the data collected, they discovered that the part of the shield had mysteriously disappeared. They found it had left the seabed when Jason tied a buoy, but when Pete Liljegren, another engineer on board, lifted the buoy to the surface, the shield was gone.

Of course, on a boat full of scientists and engineers, not everyone is easily convinced by surreal speculations. But one theory does exist, suggesting that the loss of the shield has something to do with the previous day's crab, possibly even an attempt orchestrated by a school of crabs.

But the shield is quite large, and the crabs can't have enough strength to steal them. Scientists turned their suspicions to seals, an intelligent animal. As for Chadwick, he began to worry about the devices scattered on the seabed, above his volcano.

'At some point, there was a crab waiting there… to mock us,' he said.