Sea cucumbers living at a depth of 1,000 m 'protect' king crabs

The genus Scotoplanes, also known as sea pigs, lives on the sea floor and has been seen carrying baby king crabs on its bellies and backs.

Sea cucumbers living at a depth of 1,000 m 'protect' king crabs — Researchers filmed the sea cucumber *Scotoplanes* in the deep sea. Photo: *MBARI*

Scotoplanes , or sea pigs, are a strange genus of deep-sea sea cucumbers. They use unusually long, tube-shaped legs to walk on soft mud, IFL Science reported on December 7. Long, whip-like projections called papillae extend out to find nutritious food. Their maximum body length is usually 17 centimeters. The tentacles around the sea pig’s mouth are used to dig for algae and animal debris in the mud.

A team of marine biologists from the Monterey Bay Aquarium Research Institute (MBARI) once encountered them traveling with king crabs. Using a remotely operated vehicle (ROV) called Doc Ricketts to observe the marine life living in a sunken shipping container, they were surprised to stumble upon several baby king crabs clinging to the backs and bellies of manatees for a ride.

To see if this was a common behavior, the team reviewed footage of 2,600 manatees and found that about a quarter of them were carrying crabs. The hitchhikers were mostly juvenile king crabs of the species Neolithodes diomedeae , which are about 1.4 centimeters across.

Observations of juvenile king crabs at manatee depths show that 96% of them hitchhike to manatees, but are difficult to detect due to their small size and often clinging to their underbelly. This behavior may be an effective strategy for avoiding predators.

Young king crabs need protection because there is nowhere for them to hide or burrow in the deep-sea plains (at depths of about 3,000 - 6,000 m). They are also vulnerable to attack after molting because their bodies become very soft, said the MBARI team.

Fortunately for young king crabs, at depths of 1,000 to 6,000 meters, there are many manatees that gather in large groups of up to 600 individuals. These walking “shields” provide valuable shelter. In addition, the manatees may also gain some benefits from this relationship, as the crabs help them remove parasites.

Thu Thao (According to IFL Science )

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