Analysis of a Biological Report

Analysis of a Biological Report


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Analysis of a Biological Report

Maze Learning and Memory in a Decapod Crustacean

Observation Leading to the Study

Dr Ed Pope, a marine biologist alongside other researchers, conducted a study on crabs in a maze that was designed to determine their spatial learning abilities (BBC, 2019). He states that the investigation was necessary since it was already known that insects, notably bees and ants, had remarkable mental abilities, a phenomenon that was not tested in their aquatic equivalents. A lot of studies have been conducted to determine how nesting animals, insects, in particular, navigate the challenge of finding the way between their nests and distance feeding spots. These studies have indicated that honeybees and nesting insects learn their forage roots in reference to landmarks and celestial clues. The studies also go on to discuss how these bees and insects, in general, encode the information in their brains and store it there. Dr Pope does not, however, go there with his study of crabs.

Animals set a goal beyond their current line of sight by obtaining two pieces of information from their surroundings. An animal measures its orientation by determining its current position in relation to its objective to inform which orientation is more efficient. Researchers use the metaphor of a compass to summarize the challenges animals that bring food to a central nest encounter for the ability to perceive orientation and that of a map for the ability to determine position (Collett, Chittka, & Collett, 2013).

Dr Pope continuous to explain the essence of the research on these marine creatures. He says that spatial learning is a crucial coping mechanism for animals and is understood quite well in the biological sphere in many animals but not as much in marine creatures such as crabs owing to the difficulty in following their movement. The complicated nature of spatial learning makes it essential to learn how it works in crustaceans and aquatic life in order to get a better understanding of how widespread the phenomenon is across the animal kingdom.

Research Question

The research question is about how able are European shore crabs to adapt to a complicated maze in pursuit of food in a similar manner that animals find their way to a foraging site and back to their nests. Because the habitat of decapod crustaceans is involved, three dimensional and benthic, they are more likely to adapt to life in a maze. Because of this habitat learning the location of and routes to food should be an adaptive trait among this species that can be studied using a maze. Unlike the complex mazes with challenging configurations used in studies involving insects, the ones used in this study are rather simple.


The study hypothesis is that spatial learning is a trait that is exhibited by every animal despite crustaceans having a significantly inferior brain to those of insects a species that remains the benchmark for spatial learning (Davies, Gagen, Bull, & Pope 2019). Because of the nature of their habitat, the European shore crabs are expected to possess some coping mechanism that would inform their movement in search of resources. Although it is not clear how capable these crustaceans are in spatial learning, a certain level of this capability is expected. Navigation in invertebrates is reliant on the principle of the compass, maps and landmarks, so the crabs are excepted to adopt to the maze over time and eventually find their way to the food points.

The researchers do not expect the crabs to achieve spatial learning without taking time to adopt. The only apparent unknown issue is the amount of time the crabs will take to calculate pointers such as the distance travelled and the sequential turns before visualizing the maze in its entirety. Carcinus meanas has an identifiable trait referred to in this study as wall-hugging, which is a strong character exhibited in the natural and these control conditions. This trait involves the crabs following the wall in either the left or the right side, which is a clear indication of spatial learning, although they are expected to make mistakes in the process.

To test this hypothesis, twelve European shoe crabs, scientific name, Carcinus meanas, were picked form south wales and the docks of Swansea and each put in one of the available 301 tanks connected to a seawater system recirculating at 40 000 1 (Davies et al, 2019). The researchers ensured that all the crabs placed in these tanks had not health defect, with appendages that were intact and branded according to the water tank they were placed. The researchers then left the animals to acclimate for a month. No animal died during the period of the study.

The maze included a starting chamber that was just contiguous to the entrance but not connected to the main maze with a piece of Perspex separating the two. It had a single correct path that traversed for 2 meters and required the animals to turn five times with three dead ends. The subject animals were tested each week on the same day for a month with each one of them fasted for a period of between 3 to 5 days (Davis et al, 2019). The tests included placing the maze in a large raceway tank that located in the same room as the holding tanks with both the small and large reservoirs filled with still seawater up to a depth of 10 meters. The crabs were placed at the starting pint and food (blue mussels) placed at the end of the maze. They were then given 60 seconds to acclimate before the doorway to the maze/starting chamber was opened. A high-resolution camera recorded the movement of the crabs with the absence of light and spectators (Davies et al, 2019). The trial run for 60 minutes after which it stopped or immediately the crab located the food. The recorded video was then used as the basis for calculating the time elapsed (latency) and the number of times each crab took a wrong turn.

After this conditioning study, the crabs were subjected to trials in the absence of food two weeks after the conditioning study. The trials were similar in every aspect with the conditioning study apart from the lack of food at the endpoint. The reason behind this was to investigate whether the crabs had other motivations to reach the endpoint besides food.

The results of the conditioning study were as follows:

All the crabs managed to reach the endpoint within 25 minutes in the presence of the crushed blue mussels.

The varying weights of the crabs did not influence the latency or the number of times the crabs took a wrong turn.

The latency decreased over time, creating a sloping trend from week one to week four.

The crabs did not make as many wrong turns as they did during the first week and the trend was maintained up to the last week. They made an average of 3.5 wrong turns in the first week down to an average of one by the fourth week.

The results of the trial without food were as follows:

All the conditioned crabs took only 8 minutes to find the maze’s end without food as a motivating factor, which was by a large margin higher than what was recorded during week 3 and 4 of the conditioned study.

They recorded a more significant latency than they did when food was present.

Crabs that were introduced to the trial for the first time (naïve crabs) recorded a significant difference in latency to those that were conditioned.

In conclusion, learning ability was evident in every crab, with specific animals highly interconnected against the population-average forecasts. Carcinus meanas demonstrated consistent behavior especially in exploratory comportment before and not in learning and various research investigating invertebrate learning often encounter a high level of behavioral inconsistency which may be caused by social plasticity or personality (individual character). In crabs, the results indicated individual differences owing to idiosyncrasies in plasticity as opposed to consistent personality differences. The inclusion of a naïve population proved that only food was the motivating factor for attracting the subjects to the endpoint. Although the food was crucial in navigating the crabs towards the end of the maze, conditioned crabs exhibited memory of the maze as they moved to the end with no significant differences in latency between week six and the first two weeks even in the absence of food.

Next Step for the Research

The slight increase in latency between week 6 and 4 may be an indication of the importance of the food cues but could also point at loss of memory during the two weeks the crabs stayed away from the maze. This study has significant ecological implications because it sets the foundation a model system for exploring the effects of waterborne pollutants, or changes in the chemical composition of the water, on a cultured biological and economically essential invertebrates.


BBC. (2019, October 23). Crabs crack maze to find food in study. Retrieved from, M., Chittka, L., & Collett, T. S. (2013). Spatial memory in insect navigation. Current Biology, 23(17), R789-R800.

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.