FINDING, CAPTURING, CARETAKING...RELEASING
P. crassipes are fairly common and can be found in the rocks of the intertidal of Monterey Bay, as they spend at least half of their time outside the water. Between the months of May and June, I found a handful that preferred to hang out in the medium-level tide pools, protected from wave disturbance.
Pachygrapsus are quick and cautious, constantly on the look for predators, making them difficult to capture. Simply going out without any tools or receptacles will make capturing them much more tiresome, as they can spot you coming from all directions and will scamper into small crevices, fastening themselves down with only their pincers visible. I recommend using a stick or something of the like that can fit into tiny spaces and encourage them to flee in the opposite direction (where your other hand is waiting). These metal clampers are incredibly useful for holding the crabs, as their chelipeds can leave a throbbing pinch. I have not experienced any puncturing of skin thus far.
I was rather fortunate in finding gravid females. One can quickly distinguish between males and females by noting the width of the abdomen (underside). A thin, pointy abdomen is a characteristic of a male crab, while the females have wider, rounded abdomens. The underside of gravid females will be overflowing with brown-colored eggs.
The goal of my project was to observe the gradual development of the Pachygrapsus embryos and larvae. I used a standard clear receptacle filled with seawater and various algal types that I presumed would provide cover and nutrients for the crab while I looked after her.
The female must have continuous flow of seawater. If this is unfeasible, it is possible if one changes her water every day, but make sure to do so because the combination of her respiration and that of the algae will suck the oxygen out of the receptacle quickly, and she will die if there is no escape.
My solution to this was cutting a square hole in a tupperware and taping micronmesh around the hole to permit water flow. I then filled the tupperware with rocks and algae (remember: crabs spend half of their time outside of water, so make sure there is an area where they can keep themselves dry) and placed it in a water table with running sea water. I cut a hole in the lid of the tupperware to allow aeration, and placed the lid on top to prevent the crab from escaping.
I used a glass pipette to extract eggs from the gravid females. By gently scraping the pipette against the eggs I was able to take out roughly 10 to 15 eggs to observe the stages of development over a two to three week timeframe. The female keeps water flowing over the eggs and cleans them with antibacterial, so removing them from her abdomen makes them more susceptible to bacterial attacks. One way to mitigate this is to filter the sea water in a 2 micron sieve.
Release the crabs after the eggs are developed!
Lined Shore Crab
Pachygrapsus crassipes
