To the rippling sound of an aquarium pump, a small crab comes around the corner. It moves sideways, sticking close to the walls. But when it catches sight of a mussel — laid as a reward at the end of the maze it has just walked — the crab breaks into a skipping run, throwing itself on the treat with abandon.
This crustacean, one of many shore crabs scooped by researchers from under a pier in Swansea, Wales, had just completed an intriguing feat: Without any guidance from researchers, it found its way to the end of a small maze.
According to a paper in Biology Letters on Wednesday, shore crabs can learn to navigate a lab-rat-style maze and remember it weeks later. While crabs that have never seen the maze before bump around aimlessly, experienced crabs race to the finish line with no wrong turns. The study, one of the few to look at whether crustaceans can perform such feats, suggests that crabs are quite capable of remembering routes. Maze running could also be a way to measure the effects of changes in the sea, like ocean acidification and warming, on crabs’ cognitive abilities.
Crabs often clamber through complex landscapes in their daily lives, says Edward Pope, a marine biologist at Swansea University who is an author of the new study. So, it is not particularly surprising that crabs would be able to find their way through a maze and even be able to remember it later.
What was surprising, however, was just how clear the results of the study were. During the first week of the experiment, no crabs got to the end of the maze without taking wrong turns, some of them detouring six or seven times. By week four, some could race to the end flawlessly. Even the worst-performing crab took no more than three wrong turns.
To see how the crabs would perform when there was no food in the maze, and thus no trace in the water of a snack to guide them, the researchers waited a couple of weeks and put the crabs back in the maze. They also tested crabs that had never seen the maze.
“The conditioned animals all ran to the end of the maze expecting there to be food,” Dr. Pope said.
In less than eight minutes, they scurried to the maze’s end. The inexperienced crabs, on the other hand, wandered around for up to an hour. Many never made it to the end.
The study shows that even in as little time as one exposure to the maze per week, crabs can learn the way through, and furthermore, that they remember it as much as two weeks later. The fact that the ability seems consistent across individual crabs — in other words, that it is something they can all readily do — means that could be used in future studies about how their environment affects their behavior, a focus of Dr. Pope’s work.
It’s unclear how crustaceans’ behavior may change as the oceans grow warmer and more acidic. By having crabs run a maze in water that mimics predictions for the conditions in the year 2100, for instance, the researchers hope to gain insight into whether the changes will make them slower, more confused or different in some other way from contemporary crabs.
The researchers are also considering building a more complex maze, to see what the crabs are capable of — and there is of course the question of whether a crab will remember the route through a maze beyond the two weeks tested in these experiments.
The crabs in the study, after their sojourn in the laboratory, were released where the researchers found them. Who knows? They could be scurrying around the ocean bottom off Swansea today, dreaming of mussels at the ends of mazes.
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October 24, 2019 at 06:29PM
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Happy as a Crab That Just Finished a Maze - The New York Times
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