Behavioral Study of Sand Fiddler Crabs: Uca pugilator. Sara Snider, Ruth Adkinson, Sarah Bailey, and Sarah Hunt

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1 Behavioral Study of Sand Fiddler Crabs: Uca pugilator Sara Snider, Ruth Adkinson, Sarah Bailey, and Sarah Hunt Ossabaw Experiment Dr. Claudia Melear June 26, 2006

2 Abstract: In this experiment we observed sand fiddler crabs, Uca pugilator, for a twelve hour period in their natural habitat. The observations were made a two different locations and at two hour intervals. At each interval, notes were recorded about the behaviors that were observed. These behaviors were then compiled into charts, and conclusions were made about what we saw. Introduction On Ossabaw Island our group studied the sand fiddler crab, species Uca pugilator. They are called fiddler crabs because the males have one large claw, held in front of the body like a fiddle. This claw is often lighter in color than the rest of the body, and is used by the male to attract in a courtship display procedure, characteristically different in each species of Uca. The claw also functions to warn off intruders and to establish territories. The female Uca has two small claws on the first appendages. The Uca species living on sandy beaches make about 1 ft (30 cm) deep, just below the high tide line. The sand is carried to the surface in little balls by specialized legs, and is pushed away from the entrance. Fiddler crabs rarely enter the water during their adult lives. During the spring and summer, the fiddlers only remain in their during high tide. The entrances of the are covered with sand, and contain a bubble of air, which the crabs use for respiration. When the tide recedes, the fiddlers emerge to collect food and find mating partners. Both claws of the female and the smaller claw of the male are used to scoop up sand and pass the grains to the mouthparts. Certain specialized appendages have spoon-shaped setae, used to scour organic matter from the sand grains and pass it to the mouth. The sand grains are then rejected in the form of small sand balls (Zhong). After speaking with both Patty Stinger-Barnes and Dr. Mark Alston about the sand fiddler crabs, we decided to do an initial observation of the fiddler crabs. We were fascinated with their behaviors, so we decided to conduct a behavior study on these crabs for our island experiment. After an initial observation period, we determined our focus and thus wrote our null hypothesis. Our null hypothesis was that fiddler crabs did not have specific behaviors for certain times throughout the day. We intended to prove this wrong by observing and taking notes of the various behaviors we saw. Materials and Methods: In order to conduct a behavior study of sand fiddler crabs, we split up into two groups of two and observed the crabs over a period of twelve hours. We monitored the crabs at two different locations around the campsite. Both of the observations were made at the same 3x3 foot squares each time. Location one was in the slough directly behind the pavilion. Location two was approximately one hundred yards south of location one toward the beach. During the twelve hour study, we observed the crabs for a fifteen minute period every two hours. The observations were made at 7am, 9am, 11am, 1pm, 3pm, 5pm, and 7pm. When we arrived at each observation site, the crabs scattered and disappeared into their, so we had to wait for a period of five minutes to allow the

3 crabs to return to the surface. During the fifteen minute observation period, we noted the behaviors at one minute increments. Throughout the observation, we had to be careful to not make much noise as the slightest movements would make the crabs scatter back into their. This did happen, and was taken into account when recording the observations. Results: At the conclusion of our experiment, we saw that fiddler crabs do have daily schedules. In the morning hours we observed a tendency for the crabs to eat and clean their. As the crabs clean out their, they roll up small balls of sand beneath them and pull them out of the holes. After they get out of the burrow, they pile up these small balls of sand to later eat from. The crabs, however, do not eat the sand but they eat the particles that are on and around the sand. The did more of the eating and cleaning than the males did. The males fought over both territory and. All of the fights that we observed only lasted a couple of minutes and were performed by the two crabs hooking claws and twisting back and forth. The crab that won the fight got to take over the burrow, or the female that they were fighting over. There were small fights that took place throughout the day. However, the fights in the morning were mostly over territory, whereas the fights in the afternoon and evening were over both territory and. The crabs tended only to do their mating in the afternoon and evening hours. The dance involved the males shaking their large claw up and down in a slow motion. They would mix this slow motion with a quick vibration as well. The movements got more frequent and intense when there were in the area. At location 1 we did not see very much interaction between the males and. We did see a couple of them come out of the same burrow, but we never saw them interact outside the burrow. At location 2, we did observe some male female interaction, and what seemed like more than one female trying to get on the same male. All of these observations were made at specific times during the day, and were recorded on charts. Discussion/Conclusions: The sand fiddler crabs are known for keeping tidy and always staying busy. We observed this behavior on a regular basis throughout the day. The crabs never seemed to be sitting still. However, it was noted that they did not seem to come out as much in the heat of the day. The 1pm and 3pm observations showed less movement. This could be because the crabs were in the shade and coolness of their. The morning time proved to be the time to do the heaviest cleaning and eating. Both the and males were eating and cleaning all the time, but since the males only have one claw to eat with, they generally have to eat more or quicker than the to get enough to eat. The afternoon and evening times; 3pm, 5pm, and 7pm, were when the mating began. Although not much interaction took place, the males were intensely trying to get the attention of the during this time. In order to prove the existence of a daily schedule in sand fiddler crab behavior, more in depth observations would have to be done. This could be done by watching them at more frequent intervals, or for longer

4 periods of time. However, with the time we were given, our observations show evidence that there is, in fact, some type of daily behavior routine of sand fiddler crabs. Bibliography: Alston, Dr. Mark. Conversation Stinger-Barnes, Patty. Conversation Zhong, He (Harry). Common Florida Fiddler Crabs (Uca spp.). Public Health Entomology Research and Education Center. Charts: Observations from location 1 TIME 7:00 AM 9:00 AM 11:00 AM BEHAVIORS ~ movements were slow ~ defending but no fighting ~ extremely active ~ defending the out the ~ some fighting ~ mostly males out of the burrow eating ~ less activity overall ~ males and ignoring each other ~ one male performed a short mating 1:00 PM 3:00 PM 5:00 PM 7:00 PM ~ several males were doing the mating ~ some crabs came out of the together ~ eating ~ walking around the males, possibly looking for a mate ~ males are still doing the mating ~ dancing gets intense when get close ~ less activity then at 3 ~ fighting ~ dancing ~ female fighting ~ some males interacting with, others seem uninterested

5 Observations from Location 2 TIME 7:00 AM 9:00 AM 11:00 AM BEHAVIORS ~ those eating uninterested in others ~ mating ~ no fighting ~ could not complete observations because high tide covered area 1:00 PM 3:00 PM 5:00 PM 7:00 PM ~ few eating ~ few cleaning their claws ~ dancing becomes more excited when in the area ~ less active than 3:00 PM ~ slower movements