Behavioral Response of Mud Crab Megalopae to Chemical Cues from Fish Species and Adult Conspecifics

By Jerelle Jesse

 

During the summer of 2014 OUR funded my honors research with Dr. Nancy O’Connor. This research has recently been published in the Journal of Experimental Marine Biology and Ecology and in what follows, I provide a summary of this research for the OUR blog readers.

Snapshot from the official website of the Journal of Experimental Marine Biology and Ecology, where Jesse’s research results were published

Portrait of Jerelle Jesse

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In Massachusetts, Asian shore crabs have become more abundant than native mud crabs. Crab survival can be enhanced by antipredator behaviors in response to chemical cues released by predators.

Asian shore crab

 

The purpose of this study was to determine if and how mud crab megalopae (the last larval stage of the crab) respond to chemical cues from local fish predators and adult crabs of the same species and to understand the way local mud crab megalopae behaviorally respond to chemical cues. The study focused mainly on the importance of early life stages, the origin of the chemical cues, and their ability to respond to chemical stimuli. This could potentially shed light on how an invasive species can be more successful than a native species in this habitat.

 

Mud crab megalopa

 

Female egg-bearing mud crabs were collected from the rocky intertidal habitat during low tide periods. When the females became close to releasing larvae she was transferred to a small finger bowl, then placed in the incubator.

Egg-bearing female mud crab

 

Once the larvae were released they were cared for until they reached the megalopae stage when they were designated to an experiment.

Incubator with glass bowls of mud crab larvae before reaching the megalopal stage as well as females almost ready to release larvae in small glass finger bowls

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Chemical cues for the experiment were made by the fish species or adult mud crabs being held in artificial seawater tanks to let their cue release into the water. The chemical cue seawater flowed through the apparatus, a glass pipe-shaped piece of equipment with an inflow opening, outflow opening, and a middle opening on top. The middle opening was to drop the individual megalopa into the apparatus with the cue flowing through.

The chemical cue flowed from the reservoir to a flow stabilizer, then a glass apparatus, and finally the sink. The megalopae were dropped into the middle funnel shaped opening in the apparatus

 

Once the megalopae was dropped into the apparatus it displayed 1 to 3 different behaviors then flowed out into the sink. The behaviors were categorized based on the orientation to the flow, the limb position, and the action performed. These behaviors included: control swim, random swim, perimeter swim, cyclone swim, closed roll, open roll, swim out, sideways walk run, slide, and push.

Left: Control swim; right: this megalopa happens to be on its back

 

The data were analyzed using generalized linear modeling. The results show no difference in behavioral responses between the two mud crab species. However, more open rolling behavior was seen for the mummichog cue, and significantly more walking on the bottom was seen for the adult cue. This indicates that megalopae can detect and respond to chemical cues in their environment. Megalopae can also tell the difference between adult conspecific cues and predator cues, and they can perform a different behavioral response depending on the cue.

 

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My research experiences in Dr. Nancy O’Connor’s lab are some of my best memories from my time at UMass Dartmouth. I had so much fun conducting the research that summer, then rising to the challenge of analyzing the data, and ultimately getting the opportunity to present my work at multiple conferences. It was a rewarding experience that made my career at Umass Dartmouth truly special. Currently, I am working for the Division of Marine Fisheries and applying to graduate schools. I know that this research helped me become better prepared for fieldwork and graduate school. Being able to work with a master’s student, Ami Araujo, while I was an undergraduate gave me insight to the process and hard work involved with graduate school. Without OUR’s help I would not have been able to conduct this research, and help fulfill my dream of working as a marine biologist and going to graduate school.