Creature Feature: Purple Shore Crabs


OLYMPUS DIGITAL CAMERAHave you ever been to the beach and, while climbing over by some rocks, you heard strange scurrying and scratching noises? If you did, it could be a shore crab! Purple shore crabs, hemigrapsus nudus, are found in shallow tide pools from Alaska to Baja California. They get their name from the coloring of their exoskeleton even though they can also be seen wearing greenish and brownish coloring.

The lifecycle of Purple Shore Crabs start the same as all other crabs, in eggs carried under the belly of the female. As she caries them, the female will be sure to flush water through her brood, aerating each little egg. Once the eggs hatch, they become drifting aquatic animals known as plankton. They will go through various stages until the reach their adult form. The Purple Shore Crab may appear small but that doesn’t mean it is a baby.  They are a slow-growing crab and will only reach about 2 inches at full size.

Just like human children when they grow out of their clothes, crabs grow out of their exoskeleton over time. When the crab grows, it will molt which is where it opens a hinge at the back of its carapace and pull its soft and vulnerable body out of its exoskeleton.  The crab chucks out the old exoskeleton to build a new, better fitting body casing.  When crabs are ready to mate, they will stand up and hold each other belly to belly. Together, the male and female produce about 36,000 eggs that are ready to grow! 36,000 may sound like a lot but you’ll remember that just-hatched crabs are plankton and lots of creatures in the ocean eat plankton.  Having thousands of tiny babies ensures that at least some will live to adulthood.  Those lucky babies survive to scurry around the tidepools and produce more Purple Shore Crabs.

Edited by: KC O’Shea
Pictures: MSI

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