Crabs and Lobsters

Molt of a striped shore crab
Striped shore crab semi burried in a sea anemone Striped shore crab Striped shore crab Striped shore crab hiding in rock Juvenile striped shore crab A few shore crabs hiding in pool of water

Stripes Shore Crab – ( Pachygrapsus crassipes )

These are the most commonly seen crabs in tidepools. They have a dark red and greenish colored shell with legs that have white patches. Shore crabs are very good at detecting predators and are usually seen scurrying away at the first sign of movement. They will hide in small cracks and under rocks. Shore crabs are typically one to two inches wide with larger specimens seen on occasion.
Larger hermit crab attacking smaller hermit crab
Hermit crabs feeding on algae Hermit crab feeding on algae Hermit crab juvenile hermit crabs have white stripes

Hermit Crab – ( Pagarus sp. )

Hermit crabs are unusual in that they use shells of other animals ( mainly snails ) as their homes. They seem to be always looking out for a “better” home and can frequently be seen battling other hermit crabs for the good shells. Hermit crabs are almost never seen without a shell. Hermit crabs can be identified by looking for small greenish and reddish legs protruding from a snail shell. Some have a blue stripe on the tips of their legs while others have white stripes. Adult Hermit crabs are generally about an inch long but very large specimens have been observed.

Rock Crab – (Several Species)

This crab is can be identified by an overall reddish brown color. They can grow to several inches in length and are one of the larger crabs found in the intertidal regions. These crabs are well known by seafood lovers as they are sold in restaurants and seafood stores. These crabs are found in sandy areas near the base of rocks.
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California Spiny Lobster (Panulirus interruptus )

Most visitors to the tidepools or simply beach combing will encounter a lobster, or rather the molt (shell ) of a lobster. Lobsters live in deeper water and seldom are seen in the intertidal zone. Lobsters like other crabs will shed their hard outer shell periodically. This discarded shell is called a molt and this is what most people see washed up on the beach or tidepool.

Crabs and Lobsters

Description – Crabs and Lobsters have a hard outer shell called an exoskeleton. This shell comes in many shapes, sizes and colors. Crabs are easily recognized as they have eight legs. Lobsters have ten. Two of the legs are typically larger than the others and used for feeding and defense. Crabs also have two eye stalks with eyes located at the top. The color of the shells range from white, tan, red, green and brown in color. Crabs can vary in size from less than an inch to over 2 feet for the larger Lobsters.

Feeding – Most crabs are omnivores as they will eat a wide variety of algae and other sea animals. They can frequently be seen stationary while they use their front claws to pick away at various algae. They are also good scavengers and will feed on any dead or decaying animals. Hermit crabs in particular like the giant California kelp that frequently washes ashore.

Protection – Crabs and Lobsters have a hard outer shell that protects them from predation but also prevents water loss. Crabs also have various behavioral patterns that also allow them to survive. Shore crabs have good eyesight and can see predators easily. They will quickly seek the protection of a crack or the underside of a rock. When surprised, they will on occasion jump off a higher location and free fall to the rocks and safety below.

Rock Crabs are not as fast as shore crabs and rely more on the safety of their shells than speed and behavior. They, like other crabs can curl up into a compact shape to aid in protection. Hermit crabs will simply retreat into their borrowed shells and wait for the predators to leave.

Ecology – Crabs and lobsters in order to grow must shed their hard outer shell ( exoskeleton ) periodically. This process is called molting. The crab will make a small crack in the shell and literally crawl out of their skin. The newly emerged crab is very vulnerable at this stage of its life-cycle. The shell will harden in several days depending on the species.

The cast off shell ( molt ) of the crabs are easily seen in the tidepools. Many people mistake this mold as a dead crab. These molts look pale in color but after close examination, have no internal structures or tissue. This is particularly true for Lobster molts. The tail part of lobsters is frequently seen on the sand. Female crabs in general will lay eggs and are fertilized by the males. The females will carry the eggs for several weeks until they hatch.
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