Distribution of Hermit Crabs                      28 February 2015                      Grade 10                   N. Cassello

Hermit Crab Field Report

 

Research Question:

How does the position of natural resources (trees, fresh water, ocean) affect the distribution of hermit crabs on the beach in a 5m span at noon, the hottest time of the day?

 

Hypothesis:

If the number of hermit crabs is counted with a transect line and quadrats and recorded midday, then 50% or more of them will be in or by the water in the fifth square because 12:00 pm is known as the hottest time of the day.

 

Analysis of Variables:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Background Information:

The aim of this experiment is to investigate where hermit crabs are located at midday, in relativity to the stream and the tree on the beach. The hypothesis for this lab is if the number of hermit crabs is counted using a transect line and quadrats and recorded midday, then 50% or more of them will be in or by the water because the noon is the hottest time of day.

The behavior of hermit crabs was researched. The Costa Rican hermit crabs are considered saltwater organisms. They are born as larvae in the water, but they don’t return to the water once they reach land until they have to reproduce. As stated by Mark E. Laidre in National History Magazine, “Every hermit crab, land or sea, must bear the burden of carrying its home on its back wherever it travels.” Land crabs have adapted by taking part in niche construction to have lighter, remodeled shells because of the fewer predators and less buoyancy to help pick up some of the weight.  Terrestrial hermit crabs fight over these shells because of the benefits of more room for reproduction and their growing size. Crabs are seen waiting around as bystanders for a fight in order to easily get a bigger shell. This is one reason why so many hermit crabs can bee found in such a small area. Allen Kurta of Biotropica also said, “In Costa Rica Coenobita Compressus may be found in densities as low as 3.1 crabs per m2 on sunlit, uncluttered beaches or in aggregations of up to 400 active animals per m sq. near a shaded food source.” after completing his own experiment on hermit crabs. This decapod crustacean is usually nocturnal on the beaches of the Pacific Ocean. According to Costa Rica Journey, “Land crabs require dry land to stay alive and will pass away if they are in the water for a longer period. They necessitate some water to keep their body and lungs wet… Land crabs are naturally nocturnal as it is too hot for them to be out during day time.” This statement supports the hypothesis that crabs don’t like the heat and will try to avoid it, however, it also contradicts it because terrestrial crabs don’t stay in the water for too long.

 

Apparatus:

1. 5m long transect line

2. 1m by 1m square string quadrat

3. Notebook or iPhone to record the number of crabs counted

 

Procedure:

1. Lay out the transect line from the tree to the edge of the stream.

2. Place the quadrat in the center at the end of the transect line, at the base of the tree, as shown in figure 1.

3. Count the number of crabs inside the quadrat.

4. Record the number of crabs in the notes for the corresponding quadrat.

5. Move the quadrat to the next meter mark on the same transect line, making sure to line up the edges of the two squares and to keep the square centered.

6. Repeat steps 3-5 for all 5 quadrats, until the other edge of the transect line at the stream is reached.

 

Data Collection:

Table 1: Number of Crabs Counted in each of the 5 Quadrats, which measured 1m2

 

 

 

 

 

 

 

Data Analysis:

After collecting the data with the transect line and quadrats, it was found that there was a major trend of the crabs being near the tree rather than by the stream, as shown in figure 2. There were no anomalous results in this lab because all of the data fit the same pattern of more crabs in the first quadrat and decreasing each time until the fifth. Relevant calculations include the range and difference, which is 59 because there is such a drastic change of crabs from the first quadrat to the last, with 0 crabs. Out of the 67 crabs accounted for with in the 5m by 1m span, it was found that the first quadrat held 88% of the organisms, 9% in the second, 3% in the third, and the fourth and fifth square held 0% of the hermit crabs.

 

Graph 1: Number of Crabs Counted in each of the 5 1m2 Quadrats

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Graph 2: Percentage of Hermit Crabs Accounted for in each of the 5 1m2 Quadrats

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Conclusion:

This experiment was trying to determine how the position of natural resources (trees, fresh water, ocean) affect the distribution of hermit crabs on the beach in a 5m span at noon, which is the hottest time of day. It was expected that if the number of hermit crabs is counted and recorded midday, then 50% or more of them would be in or by the water because the temperate would be so high at that specific time. A 5m transect line was laid on the ground from the base of the tree to the edge of the stream. Then, 5 quadrats, which measure 1m2, were placed consecutively on the line. The number of crabs inside each square was counted and recorded. It was found that most of the hermit crabs were within the first quadrat at the base of the tree and no crabs were in the fifth quadrat by the stream. The crabs were running away from us and using the tree roots as a hiding place. They were also staying away from the stream because it was fresh water and they are saltwater crabs. The tree was a place for socializing between the crabs and as Mark E. Laidre mentioned, the crabs were waiting either for a fight to evict a crab for their big, remodeled shell, or for group foraging. The tree was a shaded food source, which is what the crabs look for, according to Allen Kurta. The hermit crabs were shielding themselves from the sun in the heat of the day in the roots of the tree because like Costa Rica Journey said, they are naturally nocturnal and don’t like the warmth. The hypothesis of this experiment proved to be incorrect as the data shows that the hermit crabs were on or close to the tree rather than anywhere near the water.

 

Evaluation:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The method of this experiment was sufficient for producing appropriate data. The measuring instruments may not have been exact because they were pieces of strings, so the results may not have been as accurate as possible. However, the number of crabs in each of the quadrats was counted very carefully. More data could have been collected throughout the different times of day and with other weather patterns, but the data provided by the original sample was sufficient and accurate. The technique used was the best possible. Transect lines and quadrats are a good way to account for a certain number of organisms in a small area. Overall, the procedure was reliable for the research question. It allowed for the intended dependent variable of hermit crabs to be measured. The procedure and measuring equipment was appropriate for this specific lab because it accurately allowed the crabs to be counted. The controlled variables were successfully kept constant throughout the data collect. It was a quick collection, so the time of day didn’t change drastically and the same transect line and quadrat was used for each, so the size of the equipment was constant. The data is shown to be reliable and valid due to these clear and consistent trends in methodology. The results are accurate because if the experiment were to be repeated, similar results would found. However, it’s not likely the exact number of hermit crabs in each quadrat would be accounted for because they are biotic factors, which are locomotive. These results were not expected and could have been more detailed by finding more variables. The data collected was not enough because more data would have been able to be analyzed easier, but it was sufficient for the time that was given to collect it.

 

Questions for further research:

The data from this experiment raised some interesting further questions. This lab work could have been extended over different times of day. Because this specie of terrestrial hermit crab is nocturnal, it would have been interesting to see the positioning of them in the middle of the night. The research question could be, “How does the time of day (early morning, noon, evening, night) affect the distribution of hermit crabs on the beach in a 5m span?” If the light and heat were not a factor, the crabs would be more active and there would be more crabs to count, thus more of a difference in range on the transect line. This research would prove the nocturnal and social behaviors of hermit crabs.

Another possible investigation, which would take more time, could focus on the weather in which hermit crabs are most active. It would be interesting to see the behavior of the animals in the sun vs. in the clouds and rain. A possible research question could be, “How does the weather (sunny or rainy) affect the distribution of hermit crabs on the beach in a 5m span at noon, the hottest time of the day? Would they hide more from the sun or from the water? Costa Rica Journey stated that the terrestrial crabs need some water, but where does that come from? Apparently, they don’t go back to the water until they reproduce, so does the rainwater fulfill their necessity? Do the crabs need some form of freshwater? It would be interesting to observe the behavior of the crabs to see if they ever do go to the freshwater stream or if it is an irrelevant resource for them.

 

 

Works Cited:

"Hermit Crab - Costa Rica." Costa Rica Journeys. N.p., 15 Mar. 2012. Web. 27 Feb. 2015. <http://www.costaricajourneys.com/hermit-crab/>.

 

Kurta, Allen. "Social Facilitation of Foraging Behavior by Hermit Crab, Coenobita Compressus, in Costa Rica." JSTOR. Biotropica, June 1982. Web. 27 Feb. 2015. <http%3A%2F%2Fwww.jstor.org%2Fdiscover%2F10.2307%2F2387742%3Fsid%3D21105973946533%26uid%3D3737816%26uid%3D4%26uid%3D2>.

 

Laidre, Mark E. "The Social Lives of Hermits." National History. Natural History Magazine Inc., n.d. Web. 27 Feb. 2015. <http%3A%2F%2Fwww.naturalhistorymag.com%2Ffeatures%2F122719%2Fthe-social-lives-of-hermits>.