Marine Hermit Crab

Posted on April 19, 2024 by tspuckler

Often when I look in a tidepool I see nothing of interest. By if I stare into the water long enough, I’ll start to see small creatures reveal themselves by their movements. Most of these inhabitants are well-camoflauged and only their activities give them away. A great example of this is the Marine Hermit Crab.

There are over 500 species of hermit crabs around the world, and they’ve evolved a unique body shape to fit into their shell homes. Unlike free-living crabs, their abdomens aren’t covered in a hard exoskeleton but rather a thin, soft one; their abdomens are also twisted to fit the spiral cavity of the snail shells in which they make their homes. Some species live mostly on land, while others rarely leave the water.

Like all crabs, the Marine Hermit Crab is a decapod — it has five pairs of legs, including a pair of claws. It uses its claws for defense and food shredding as well as eating. The second and third pairs of legs help the crab walk, and the last two pairs hold the crab in its shell.

Hermit Crabs are pretty easygoing about what they eat. In fact, they’ll dine on just about anything they can find in the water that surrounds them – including small fish, invertebrates such as worms, plankton and any food particles that happen to be floating by.

Hermit Crabs don’t kill the snails in whose shells they make their homes. They’re actually able to smell dead or dying snails, which can lead them to a potential shell. But competition for such shells can be fierce. They may fight to the death in pursuit of a shell. And, as they grow, they must seek out new shells in which to live.

Contrary to their name, hermit crabs live very social lives. They live in big groups, travel together and even meet up to search for food and shells.

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Louisiana Swamp Crayfish

Posted on March 15, 2024 by tspuckler

I have found this brightly colored crustacean while visiting both southern Nevada and southern California.

The Lousiana Swamp Crayfish is found in rivers, bayous, swamps, ditches, ponds, lakes, and rice fields throughout the southcentral United States and northeastern Mexico. It seems to prefer flooded wetland habitats with periodically flowing, well-oxygenated water. This species retreats into burrows when surface water dries up.

This creature is a physical ecosystem engineer, constructing burrows consisting of a single opening, which may be covered with a mud plug or raised above ground level in the form of a chimney to reduce evaporative loss further from the water’s edge. The opening leads to a tunnel which widens to an enlarged chamber at the end.

Crayfish are opportunistic omnivores. They can detect small amounts of blood and decomposition scents in the water to track down and feed on partially decomposed plant material, living soft plants, and virtually any type of animal matter.

The Lousiana Swamp Crayfish is a very successful invasive species. Not only can it be found in many parts of the United States where it is not native, but can also be found in inland waters on all continents except Australia and Antarctica. In the United States it is readily available though the biological supply trade and specimens and is sometimes released following classroom or laboratory use. It is also popular among anglers as bait for Largemouth Bass.

Part of the reason it is now found in other countries is importation for crayfish farming. Eating freshwater crayfish is common in many countries. The first known introductions of this species took place in the 1920s: 1924 in California and 1927 in the Hawaiian Islands, 1927 in Japan, and 1929 in China. In the mid-1960s, a batch of crayfish was sent to Uganda and Kenya, and soon afterwards, to other African countries.

The life cycle of the Louisiana Swamp Crayfish is relatively short, with an onset of sexual maturity occurring in as few as two months and a total generation time of four and a half months. Although they look attractive (for a crustacean), this species competes aggressively with native crayfish species for food and habitat.

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Purple Shore Crab

Posted on April 14, 2023 by tspuckler

I found this cool creature while tidepooling on the California Coast. Crabs come in many shapes and sizes, but they have a few things in common – usually ten jointed legs and eyes at the ends of short stalks.

The Purple Shore Crab can be found sheltering under rocks in inter-tidal areas along the west coast of North America. They are quite adaptable, being found from the frigid shores of Alaska all the way to the sunny beaches of Baja California.

These crustaceans look for food during low tide at night on top of rocks and on nearby sandy beaches. They feed on green algae, snail eggs, smaller animals and more. On the flip side, for their part, they’re eaten by scoters (a type of sea duck), fish and gulls.

Purple Shore Crabs are rarely found in water deeper than three feet. They prefer rocky coastlines where hiding places are plentiful, because they do not burrow in sand, like many other crabs.

They have the ability to regulate the amount of salt in their systems, a trait called osmoregulation. This enables them to live rather far into brackish estuaries and salt marshes, where the the level of salt in the water changes with the tides.

The mating ritual of purple shore crabs involves a bizarre dance during which males and females rise up and embrace, belly to belly. The males clasp females firmly with their legs and claws, and fall over backwards.

The Purple Shore Crab truly was a fun find on my California trip.

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Stout Shrimp

Posted on March 31, 2023 by tspuckler

While tidepooling on the Pacific Coast, we found a few of these cool and colorful creatures.

The Stout Shrimp is one of several species of shrimp with the common name “Broken Back” Shrimp, named for the sharp angle of the attachment of its tail to its body.

This crustacean’s color is highly variable, ranging from white mottling or stripes to browns and greens. It regularly occurs in the intertidal zone or along the sides of floats, where they are often the most commonly seen shrimp.

The Stout Shrimp is nocturnal and comes out at night to forage for food. During the day they can be found under seaweed, hidden around rocks or nestled among mussels.

It is mainly carnivorous, feeding on a variety of small animals. In turn, it is eaten by a variety of fish…but only if the fish can catch them. Like crayfish, these shrimp use the rapid flexing of their tail to scoot away from danger.

Although small, these fine invertebrates were a fun find while exploring California.

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Striped Shore Crab

Posted on May 20, 2022 by tspuckler

While visiting Point Reyes National Seashore in California, I hiked along small waterways in a cattle grazing area and saw a number of these neat crustaceans.

Typically this crab is brown-to-purple or black with green stripes. Though this color combination makes it eye-catching when seen out in the open, it also helps the crab disappear into dark, rocky crevices where it hides in sea lettuce, rock weed and bits of kelp.

Although there can be aggressive intraspecies competition over food, this creature does not keep a territory to defend. It can spend over half of its time on land and will purposely submerge to wet its gills; it can sustain itself out of water for up to 70 hours.

Striped Shore Crabs live along the West Coast of North America, from Mexico in the south, to Vancouver Island, Canada, in the north. In additional to cattle grazing fields, they reside in estuaries, tidepools, mussel beds and in the burrows they sometimes dig into sandy banks. They can sometimes be seen scuttling along shoreline rocks.

The variety of habitats where they exist mirrors the variety of foods they’ll eat. Though they feed mostly on phytoplankton growing on the water or rocks around them, they are opportunistic and will also eat animals including dead fish, limpets, snails, isopods, worms and mussels.

Striped Shore Crabs were an unexpected and fun find while on my visit to the Golden State.

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Kelp Crab

Posted on March 11, 2022 by tspuckler

We found several of these super cool crustaceans while tidepooling in California. Like other members in their family, they have very tough exoskeletons to protect them from predators.

These crabs belong to a large group called “Spider Crabs.” They generally have long legs with relatively small body. Their carapace (back shell) somewhat resembles a five-pointed sheriff’s badge; it is smooth and is longer than it is wide.

This species is usually dark brown. Kelp Crabs, as their name implies, are typically associated with their namesake plant and they are colored much like kelp. Their legs end in sharp points, which are used to cling to slippery surfaces.

These creatures are herbivores most of the time. During the Summer they nip off bits of brown algae such as kelp, rockweed and sea cabbage, as well as several types of red algae. When the algae die back during Winter, they turn to an animal diet, including small mussels and barnacles.

Kelp Crabs are found in rocky intertidal areas, kelp beds and around structures such as pier pilings. In the Fall, adults move to deeper water where they congregate, feed and mate. They use kelp beds not only for food, but also as shelter against predators such as Sea Otters.

These creatures will sometimes attach pieces of kelp to the points on their carapace, saving them to eat later. While these long-legged invertebrates look delicate, they are stronger than you may think and are able to give forceful pinches with their front claws.

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Flattop Crab

Posted on March 12, 2021 by tspuckler

This was a tiny, but super cool find while tidepooling on the California coast. A member of the Porcelain Crab Family, it shares the general body plan of a squat lobster, but their bodies are more compact and flattened – an adaptation for living and hiding under rocks.

These are quite fragile animals and often shed their limbs to escape predators, hence the family name “Porcelain Crab.” What struck me the most about this creature was its oversized claws which it uses to defend its territory.

Flattop Crabs are an example of carcinisation, whereby a noncrab-like animal (in this case a relative of a squat lobster) evolves into an animal that resembles a true crab. They can be distinguished from true crabs by the apparent number of walking legs (three instead of four pairs) and the long antennae located on the front outside of the eyestalks.

These crustaceans feed by combing plankton and other organic particles from the water using long bristle-like structures on their mouthparts. At a a shell size of less than one inch across, its prey is quite small, mainly consisting of diatoms.

The Flattop Crab can be found in the lower intertidal of sheltered waters. Its range extends from southeastern Alaska to southern California. It prefers areas with strong currents and can be found under rocks, especially those embedded in gravel or sand under seaweed and mussel beds in both exposed and sheltered shores.

This was an awesome find on my Golden State adventure.

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Marsh Crab

Posted on September 28, 2019 by tspuckler

While staying at North Beach, Maryland, I would often see these crustaceans in rock piles that bordered the brackish water shorelines. They were shy and would quickly retreat into their rock hideout if they felt they were being watched or approached.

The Marsh Crabs live communally within interconnected burrows in the mud. The tunnels may be 2 to 3 feet deep and often filled with water. Males are known for making “rapping” sounds when defending their burrows by striking two of their legs together.

Though I saw them in the daytime, they are mainly nocturnal. These invertebrates eat the outermost leaves of marsh plants, especially cordgrass.

Sometimes known as Squareback Marsh Crabs, these creatures live in a marine environment, but do not require seawater to survive, making them true terrestrial crabs.

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Red Rock Crab

Posted on January 19, 2019 by tspuckler

As its name implies, this crustacean is often found in and around rocky places and features reddish-purple coloration.

It can grow to more than 10 inches across, but 4 to 6 inches is more common. Its large claws are tipped in black and they have a wide, fan-shaped body.

This cool creature crushes barnacles with its large pincers and eats them. It also eats smaller crabs, sea cucumbers, and many other intertidal invertebrates, as well as dead fish.

While searching tidepools, I saw this “shell” move. It didn’t take long to realize that it was not a shell at all, but rather a juvenile Red Rock Crab, which can be white with a pattern of dark lines.

I enjoy finding these hard-shelled creatures, whose other common names include Red Crab, Cancer Crab and Red Cancer Crab.

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Asian Shore Crab

Posted on September 15, 2018 by tspuckler

While visiting New York last week, I flipped a few rocks along the East Coast and encountered quite a few of these small crustaceans; they were often found in dense aggregations.

Adults are small, measuring about an inch and a half in shell width. They have a squarish shell and light and dark bands on their legs.

Though native to the western Pacific Ocean from Russia to Hong Japan, it is likely that Asian Shore Crabs were discharged at harbors in the United States as larvae from the ballast water of a cargo ship.

This creature is not a picky eater, and feeds on a wide range of plants and animals. It can tolerate a wide range of environmental conditions. These characteristics help to make it successful in areas where it is not native.

Although undeniably cute, Asian Shore Crabs have displaced both large and small native crabs along the East Coast.

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Category Archives: Crustaceans

Marine Hermit Crab

Louisiana Swamp Crayfish

Purple Shore Crab

Stout Shrimp

Striped Shore Crab

Kelp Crab

Flattop Crab

Marsh Crab

Red Rock Crab

Asian Shore Crab