How do hagfish burrow into deep-sea sediments?

Zoom in / A sixgill hagfish (Heptadretus Hexatrema) in False Bay, South Africa.

The humble hagfish is an ugly, gray, eel-like creature best known for its ability to unleash a cloud of sticky slime on unsuspecting predators, gagging and suffocating them. That is why it is affectionately called „”.snot snake„Hagfish like to burrow into deep-sea sediment, but scientists have not been able to observe exactly how they do it because the dark sediment obscures the view. Chapman University researchers created a special tank with transparent gelatin to overcome this challenge. In one step, get a more complete picture of burrowing behavior. New paper Published in the Journal of Experimental Biology.

„We’ve known for a long time that hagfish can burrow in soft sediments, but we didn’t know how they do it,” said co-author Douglas FudgeWho is a marine biologist? He heads the laboratory Chapman devoted himself to the study of hagfish. „By figuring out how to get hagfish to voluntarily burrow on transparent gelatin, we were able to see this process for the first time.”

As previously reported, there were scientists Hawkfish Slim reads It has been an unusual item for years. It’s not like mucus, which dries up and hardens over time. Hagfish slime is slimy, giving it the consistency of semi-solidified gelatin. This is due to the long, thread-like fibers in the mucus, in addition to the proteins and sugars that make up mucin, the other main components. Those fibers coil into „skins” that resemble balls of yarn. When hakefish are loosened by a slime, the skins loosen and combine with salt water, blowing up to 10,000 times their original size.

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From a material standpoint, hagfish slime is a fascinating material that could one day be useful for biomedical devices, or for weaving light-but-strong fabrics for natural Lycra or bulletproof vests, or for lubricating industrial drills that can get stuck in deep soil and sediment. In 2016, a group of Swiss researchers Studied unusual fluid properties Hawkfish slime, in particular, focuses on how those properties provide two distinct advantages: helping the animal protect itself from predators and tying itself into knots to escape from its own slime.

Hagfish mud is a non-Newtonian fluid, unusual in that it is both shear-thickening and shear-thinning in nature. Most hagfish predators use suction bait, which creates a shear-thickening flow in one direction, best to clog the gills and choke, hunters said. But if the hagfish needs to extricate itself from its own mud, its body movements create a shear-thinning flow that adjusts the slimy network of cells that make up the mud.

Has become fudge Reading the Hawkfish and properties of its mucus over the years. For example, in 2012, when he was at Fudge’s lab at the University of Guelph Successfully harvested Hagfish slime is dissolved in liquid and then „spun” into a strong-yet-stretchable thread, much like spinning silk. Such threads could replace the petroleum-based fibers currently used in safety helmets or Kevlar vests, among other potential applications. And in 2021, his team Found it Slime produced by large hagfish has much larger cells than slime produced by small hagfish—an unusual example of cell size scaling with body size in nature.

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A sediment solution

This time, Fudge’s team turned their attention to hagfish drilling. In addition to shedding light on hagfish reproductive behavior, the research may have broader ecological implications. According to the authors, burrowing is an important factor in sediment turnover, while pore aeration changes the chemistry of the sediment, making it more oxygenated. This can change which organisms can thrive in that sediment. Understanding drilling mechanisms can also help in the design of soft drilling robots.

Drilling footage for a hagfish digging through transparent gelatin.
Zoom in / Drilling footage for a hagfish digging through transparent gelatin.

TS Fudge et al., 2024

But first Fudge’s team had to figure out how to see through the sediment to observe the burrowing behavior. Other scientists studying different animals have relied on transparent substrates such as the mineral cryolite or gelatinized hydrogels, the latter of which have been successfully used to monitor the burrowing behavior of polychaete worms. Fudge et al. Gelatin was selected as the sediment substitute and placed in three custom transparent acrylic chambers. They filmed the gelatin-piercing behavior of 25 randomly selected hagfish.

It was implemented by Fudge et al. To identify the two distinct phases of movement used by hagfish to create their u-shaped burrows. First there is the „thrash” stage, in which the hagfish swims vigorously while moving its head from side to side. This not only helps propel the hagfish forward, but also cuts the gelatin into chunks. This may be the hagfish’s way of coping with the challenge of creating an opening in the sediment (or gelatin substrate).

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Next comes the „whirling” phase, which is driven by the „internal concert” common to snakes. It involves contraction and forceful stretching of the body, as well as bracing and expanding the lateral forces on the walls. „A snake using concertina movements would achieve steady progress through alternating waves of stretch and contraction through a narrow channel or hole,” the authors wrote, and the hagfish’s loose skin is well-suited for such a strategy. The wriggling phase lasts until the burrowing hagfish pulls its head out of the substrate. Hawkfish took an average of seven minutes or more to complete their burrows.

Naturally there are some caveats. The walls of the acrylic containers may have affected the drilling behavior or the final shape of the holes in the laboratory. The authors recommend repeating the experiments using sediments from their natural habitat, implementing X-ray videography of the hagfish fitted with radio markers to capture movements. Body size and substrate type can also influence burrowing behavior. But overall, they believe their observations are „an accurate representation of how hagfish build and move within burrows in the wild.”

DOI: Journal of Experimental Biology, 2024. 10.1242/jeb.247544 (About DOIs).

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