Green Porcelain Crab Picture
Latin Name: Petrolisthes armatus
Species: Marine Invertebrate
Conservation Status: SNA/Exotic
The green porcelain crab is a small marine invertebrate with a mottled green-brown exoskeleton and distinctive light and dark bands along its legs. Its claws measure about three to four times longer than they are wide. They are long, flattened, and lack a carpus—a major leg segment that acts as a crab’s “wrist”. The crab’s rounded shell (carapace) measures up to 1 cm wide and has tiny ridges and granules. One of its key identifying features is its long, backward-facing antennae positioned outside of the eyes rather than between them. Its mouthparts are a striking metallic turquoise or bright blue and are feathery in texture.
Range & Habitat (map)
Green porcelain crabs are commonly found in intertidal zones, hiding among rocks and debris in tide pools and along shorelines. They also thrive in shallow subtidal (underwater) areas with sandy or rocky bottoms. Oyster reefs and mangrove roots provide shelter and feeding opportunities, making them a frequent habitat for these crabs. They are also observed around dock pilings and other submerged structures. Native populations are found in the northern Yucatán, Gulf of Mexico, and southeastern Florida. In the United States, non-native populations now span coastal regions from Cape Hatteras, North Carolina, to central Florida. Populations are also found along the coasts of Peru, Brazil, and Baja California.
Diet
Green porcelain crabs are opportunistic suspension feeders that capture food particles suspended in the water column. Their diet primarily consists of decomposing organic matter, known as detritus, which provides essential nutrients. They also consume microalgae—tiny algae drifting in the water—which serve as a major food source for many aquatic organisms.
Life History
Female crabs carry sponge-like egg clusters beneath their bodies, producing anywhere from 25 to 900 eggs depending on size. When the eggs hatch, larvae drift in the water before developing small appendages and eventually settling on the seafloor as tiny juvenile crabs. Over time, they grow into adults, and females can produce broods each time they molt—about every six days.
Significance
The green porcelain crab is a non-native, invasive species that was accidentally introduced to the United States in the 1930s. Since then, it has become widespread along the East Coast, from the Florida Keys to North Carolina. Its rapid spread has disrupted local ecosystems, particularly oyster beds in South Carolina and Georgia. The species competes with native crabs for food and habitat, leading to declines in native populations. Its presence has also been linked to increased numbers of oyster drills—small predatory sea snails—which further stress oyster habitats.
Threats & How You Can Help
Because green porcelain crabs spread so quickly, they can easily cause long-term ecological problems. Human activities such as ballast water discharge from ships, fouled hulls, and the movement of oyster beds often introduce them to new areas. You can help by supporting policies that regulate ballast water and oyster transplant practices, volunteering with conservation groups to track invasive species, and staying informed about invasive marine life. Businesses involved in oyster restoration should carefully inspect equipment and transplant sites to prevent further spread.
Additional Info
Green porcelain crabs tolerate a wide temperature range, surviving in waters as cold as 6°C and as warm as 40.5°C. They can persist in salinities as low as 20 parts per thousand. Adult sizes typically range from 3 mm to 14 mm.
Additional Resources
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