you're reading...


Mazes aren’t just for mice: European shore crabs exhibit spatial learning

Davies, R., Gagen, M. H., Bull, J. C., & Pope, E. C. (2019). Maze learning and memory in a decapod crustacean. Biology Letters, 15(10), 20190407. https://doi.org/10.1098/rsbl.2019.0407

Crabs spend their time scrambling along the sea floor, a complex three-dimensional environment that they scour in search of food. European shore crabs (Carcinus maenas) can be found in intertidal zones and shallow seas, where they feed on just about anything they can find. Given the complexity of their environment, it makes sense that a crab may need to remember the different paths it took in order to find various resources, like food. Mazes used in scientific studies may have multiple turns and dead-ends and are thus a good representation of the sorts of difficult natural arenas that crabs must make their way through to find food on a daily basis.

A European shore crab (Carcinus maenas) on a beach. Source: John Haslam

For the most part, studies using some of these more complex mazes with multiple turns and dead-ends have been used to study vertebrates, and particularly lab mice. Vertebrates are usually considered the more advanced group when it comes to learning, and especially the challenges of spatial learning. But based on a recent test of crab performance in a complex maze, it appears that crustaceans should be added to this list of maze-learning animals.

A recreation of the maze used in the study.

To conduct their experiments, researchers placed food (a crushed mussel) at one end of the maze and crabs at the other, enticing the crabs to find their way through to the end. After placing the crab in the maze, everybody exited the room, leaving behind a video camera to record the crab’s journey. The researchers did this for twelve crabs over the course of four weeks and saw that the time it took crabs to find the end of the maze and the number of wrong turns they took decreased with experience. It appeared as though crabs were remembering how they had navigated in the past.

Blue mussels (Mytilus edulis) are a preferred prey of European shore crabs, and were placed at the end of the maze to reward crabs. Image credit: Emőke Dénes

The final stage of this study took place six weeks after the first crabs were tested. During this final step, a new set of crabs in addition to the ones which had previously spent four weeks learning the maze were both tested, but this time without a food reward placed at the end. Although the experienced crabs performed worse than they had two weeks previously when there was food at the end of the maze, they still performed better than the naïve crabs which were making their way through the maze for the first time. Since the only difference between the two groups of crabs was their experience in the maze, this is likely what caused a different outcome in their maze performance. Even without a food reward, the experienced crabs still performed better, an indication that some kind of learning had occurred to cause that difference.

Crab maze learning is an exciting development, but it also raises a number of interesting questions. Why did the crabs perform worse two weeks later? Was it because they forgot how to navigate the maze, because they no longer had a food reward to motivate them, or because of some other difference we haven’t thought of? How were the crabs actually learning and remembering how to get through the maze? How do these mazes relate to the crabs’ natural habitat? How long does a crab’s memory of its environment last and how does that relate to the rapid change of coastal environments from waves, weather, and tides?

Studies regarding these sorts of intangible processes, like learning, are particularly difficult since we can’t always see the change occurring in an animal. But studies like this also remind us how little we know about the cognitive processes of other animals, particularly complex invertebrates like crabs, and it is an exciting prospect to think about what direction studies will take us next.


No comments yet.

Post a Comment


  • by oceanbites 3 months ago
    Happy Earth Day! Take some time today to do something for the planet and appreciate the ocean, which covers 71% of the Earth’s surface.  #EarthDay   #OceanAppreciation   #Oceanbites   #CoastalVibes   #CoastalRI 
  • by oceanbites 4 months ago
    Not all outdoor science is fieldwork. Some of the best days in the lab can be setting up experiments, especially when you get to do it outdoors. It’s an exciting mix of problem solving, precision, preparation, and teamwork. Here is
  • by oceanbites 5 months ago
    Being on a research cruise is a unique experience with the open water, 12-hour working shifts, and close quarters, but there are some familiar practices too. Here Diana is filtering seawater to gather chlorophyll for analysis, the same process on
  • by oceanbites 6 months ago
    This week for  #WriterWednesday  on  #oceanbites  we are featuring Hannah Collins  @hannahh_irene  Hannah works with marine suspension feeding bivalves and microplastics, investigating whether ingesting microplastics causes changes to the gut microbial community or gut tissues. She hopes to keep working
  • by oceanbites 7 months ago
    Leveling up - did you know that crabs have a larval phase? These are both porcelain crabs, but the one on the right is the earlier stage. It’s massive spine makes it both difficult to eat and quite conspicuous in
  • by oceanbites 7 months ago
    This week for  #WriterWednesday  on  #Oceanbites  we are featuring Cierra Braga. Cierra works ultraviolet c (UVC) to discover how this light can be used to combat biofouling, or the growth of living things, on the hulls of ships. Here, you
  • by oceanbites 7 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Elena Gadoutsis  @haysailor  These photos feature her “favorite marine research so far: From surveying tropical coral reefs, photographing dolphins and whales, and growing my own algae to expose it to different
  • by oceanbites 8 months ago
    This week for  #WriterWednesday  on Oceanbites we are featuring Eliza Oldach. According to Ellie, “I study coastal communities, and try to understand the policies and decisions and interactions and adaptations that communities use to navigate an ever-changing world. Most of
  • by oceanbites 8 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Jiwoon Park with a little photographic help from Ryan Tabata at the University of Hawaii. When asked about her research, Jiwoon wrote “Just like we need vitamins and minerals to stay
  • by oceanbites 8 months ago
    This week for  #WriterWednesday  on  #Oceanbites  we are featuring  @riley_henning  According to Riley, ”I am interested in studying small things that make a big impact in the ocean. Right now for my master's research at the University of San Diego,
  • by oceanbites 8 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Gabby Stedman. Gabby is interested in interested in understanding how many species of small-bodied animals there are in the deep-sea and where they live so we can better protect them from
  • by oceanbites 9 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Shawn Wang! Shawn is “an oceanographer that studies ocean conditions of the past. I use everything from microfossils to complex computer models to understand how climate has changed in the past
  • by oceanbites 9 months ago
    Today we are highlighting some of our awesome new authors for  #WriterWednesday  Today we have Daniel Speer! He says, “I am driven to investigate the interface of biology, chemistry, and physics, asking questions about how organisms or biological systems respond
  • by oceanbites 10 months ago
    Here at Oceanbites we love long-term datasets. So much happens in the ocean that sometimes it can be hard to tell if a trend is a part of a natural cycle or actually an anomaly, but as we gather more
  • by oceanbites 10 months ago
    Have you ever seen a lobster molt? Because lobsters have exoskeletons, every time they grow they have to climb out of their old shell, leaving them soft and vulnerable for a few days until their new shell hardens. Young, small
  • by oceanbites 11 months ago
    A lot of zooplankton are translucent, making it much easier to hide from predators. This juvenile mantis shrimp was almost impossible to spot floating in the water, but under a dissecting scope it’s features really come into view. See the
  • by oceanbites 11 months ago
    This is a clump of Dead Man’s Fingers, scientific name Codium fragile. It’s native to the Pacific Ocean and is invasive where I found it on the east coast of the US. It’s a bit velvety, and the coolest thing
  • by oceanbites 12 months ago
    You’ve probably heard of jellyfish, but have you heard of salps? These gelatinous sea creatures band together to form long chains, but they can also fall apart and will wash up onshore like tiny gemstones that squish. Have you seen
  • by oceanbites 12 months ago
    Check out what’s happening on a cool summer research cruise! On the  #neslter  summer transect cruise, we deployed a tow sled called the In Situ Icthyoplankton Imaging System. This can take pictures of gelatinous zooplankton (like jellyfish) that would be
  • by oceanbites 1 year ago
    Did you know horseshoe crabs have more than just two eyes? In these juveniles you can see another set in the middle of the shell. Check out our website to learn about some awesome horseshoe crab research.  #oceanbites   #plankton   #horseshoecrabs 
WP2Social Auto Publish Powered By : XYZScripts.com