STONE CRABS
When you mention crabs around here, we automatically think of our Blue Crabs – the ones
that we catch and love to eat. They can swim fast by using their paddle-like back legs, and are
agile, quick runners along the bottom where they search for anything they can grab with their
lightning-fast pinchers. But occasionally around here you will come across another large crab,
the Stone Crab.
I’m not sure why they are called Stone Crabs. It might be because of their round, stone shape,
or possibly because of their thick rock-hard exoskeleton. Or it may be because they are often
found among rocks, jetties and other hard structures. A Stone Crab is not a swimmer, but more
of a clinger. It doesn’t have any paddle-like swimming legs, but instead has sharp pointy ends on
all its walking legs that it uses for gripping onto rocks or for digging into the sand.
Medium to large Stone Crabs are dark brown, but when they are young they might be a little
more colorful, ranging from dark blue to purple. In order to grow, they have to molt because
their thick, hard exoskeleton won’t stretch. When it molts, a crack forms between the back legs,
then the upper and lower halves of its exoskeleton will separate, and the Stone Crab will come
out backwards, leaving its old exoskeleton behind. When it comes out, its new skin is soft and
flexible. It will take in seawater into every cavity inside its body, causing its body to swell up and
instantly become larger; and there would be no way it could fit it back into its old exoskeleton.
Over the next few days, its new skin will gradually get harder and thicker, and it will be that size
until it molts again.
The distinctive characteristic of a Stone Crab is its pair of huge, muscular claws. Often, one is
slightly larger than the other, but both are big and strong. They use these claws to crush things
– not just to pinch – but to crush. From what I’ve read, a Stone Crab claw can produce up to
19,000 pounds of force per square inch. With that kind of force, they can certainly eat any other
invertebrate they can catch, but mostly they crush and eat oysters and barnacles.
Stone Crabs can live up to 7 or 8 years, so they can get fairly large, and those claws can get
pretty massive. People don’t usually eat Stone Crabs like we do Blue Crabs, but we sure do eat
those claws! Most states allow you to break off and keep one of the claws and then throw the live
crab, with its other claw still intact, back into the water. That way it still has a claw for defense
and for feeding. When it molts, it will emerge and have its second claw back again. At first it will
be a little smaller than it was originally, but after another molt or two, that second claw will be
as big as it was before.
We get a few Stone Crabs around here, but most are harvested commercially in south Florida.
You can find Stone Crab claws in some of our local seafood markets and Tybee restaurants.
Dr. Joe Richardson (Ph.D. Marine Sciences) is a retired marine science professor with 40 years
of research and teaching experience along GA, the southeastern coast and Bahamas. Besides
research, he conducts Tybee Beach Ecology Trips (www.TybeeBeachEcology.com) and frequently
posts pictures of their findings on his Tybee Beach Ecology Trips Facebooks page.
Beach Walks
with Dr. Joe
By Dr. Joe Richardson
20 TYBEE BEACHCOMBER | SEPT 2018
/(www.TybeeBeachEcology.com)