Seasonal hepatopancreas fatty acid (HFA) content of the striped shore crab, Pachygrapsus crassipes, in Southern California

Click here to open her Thesis (pdf)

Picture this... scrambling over rocks in search of the ever-elusive and fascinating crustacean, the shore crab Pachygrapsus crassipes. This is one of the best places on earth to work with breath-taking waves, salty air, and tide pools swarming with life. What more could you ask for? Welcome to my life for the next year! Every other month I have the opportunity to gather my accomplices and drive out to the coast for a day of fun and excitement. Easy, you may say? Guess again! These laterally-racing critters are a lot harder to catch than they might seem, as they are not only able to disappear into the tiniest of cracks and crevices, but they are also equipped with an efficient pair of pinching claws they are usually not afraid to use.

Once a crab has been successfully cornered and coerced to enter the plastic container, I'm still not scott-free. Each crab has to be weighed and sexed before I can decide whether or not to keep it. If the crab is less than 5 grams or over 10 grams, all that hard work going in to the capture of that individual is gone and the crab is free to go. Likewise, I search for 10 males and 10 females and must reach that quota before calling it quits for the day. In addition, if a female happens to be carrying eggs, I allow her to run free and be a mother.

The reason I am so rigorous in deciding who to keep and who to set free is to maintain a balance of males and females and to rule out size as a factor in my results. But catching these guys is only the beginning of the long, arduous road to determine the fatty acids present in each animal. They are sacrificed prior to transport back to the lab to reduce stress-induced lipid metabolism.

Once arriving at the lab, the carapace width and length is measured, and I dissect out the hepatopancreas. This organ has many names, including the liver and digestive gland. It functions in some digestion and is the main location of fat storage, hence the reason it is the target of my research.
Click here for Pachygrapsus crassipes Dissection Guide
After dissection, the hepatopancreas is then stored at -80ºC until I have the chance to continue on with the process. The longest part, so far, is extracting the lipids from the hepatopancreas and deriving the methyl ester form for analysis. It's an exciting process that takes approximately 2.5 hours per sample!

They are then returned to storage at -80ºC and wait to be taken out to the University of California at Riverside Gas Chromatography (GC) Lab. Once there, each sample is injected into the gas chromatographer/mass spectrometer (GC/MS) individually and analyzed for lipid content, both identification and qualification. The results are then analyzed using computer software, and entered into a database to be compared with my previous results.

They are then returned to storage at -80ºC and wait to be taken out to the University of California at Riverside Gas Chromatography (GC) Lab. Once there, each sample is injected into the gas chromatographer/mass spectrometer (GC/MS) individually and analyzed for lipid content, both identification and qualification. The results are then analyzed using computer software, and entered into a database to be compared with my previous results.

My objective in this research is to test the hypothesis that fatty acids found in the hepatopancreas change on a seasonal basis as well as between sexes. This could be important in understanding how these crabs are able to survive in the fluctuating environment in which they live. Changes in these fatty acids could be an adaptive mechanism used by Pachygrapsus crassipes to take advantage of the biochemical properties of fatty acids in different temperatures. Because fatty acid viscosity changes with fluctuations in temperature, it may be beneficial for them to store different types of FAs in different seasons. Changing fatty acid saturation and length with fluctuations in temperature could maximize the utilization of these energy stores, allowing Pachygrapsus to thrive in the variable conditions of the intertidal zone. Their survival may influence the dietary preferences of other intertidal animals that depend on them as a food source. I plan to look at the difference in fatty acid concentration between males and females over the course of one year.