Hawaii’s coastal waters are home to a diverse array of crustaceans, with nearly 200 species of crabs inhabiting its shores and reefs.
These fascinating creatures come in various shapes, sizes, and colors, playing crucial roles in the islands’ marine ecosystems.
From the tidepools to the deeper ocean floors, Hawaiian crabs have adapted to thrive in different habitats, each with its unique characteristics and behaviors.
The most common types of crabs found in Hawaii include the ‘a’ama rock crab, kūhonu swimming crab, and ‘alakuma pebble crab.
These species are not only important to the local ecosystem but also hold cultural significance for native Hawaiians.
Some, like the ‘a’ama, have been traditionally harvested for food, while others are revered in Hawaiian folklore and legends.
Exploring the world of Hawaiian crabs reveals a captivating microcosm of marine life.
From the tiny harlequin crab that lives symbiotically with sea cucumbers to the larger and more conspicuous species found in tidepools, each crab has its own unique story to tell.
Understanding these crustaceans not only enriches our knowledge of marine biodiversity but also highlights the importance of preserving Hawaii’s delicate coastal environments.
1. Hawaiian Red Rock Crab (‘A’ama)
The Hawaiian Red Rock Crab, known locally as ‘A’ama, is a common sight along Hawaii’s rocky shorelines.
Its scientific name is Grapsus tenuicrustatus, and it belongs to the family Grapsidae.
These agile crustaceans are well-adapted to their coastal habitat.
They have a flattened body shape that allows them to squeeze into narrow crevices for protection.
Their strong legs enable them to scamper swiftly across rocks and even jump short distances.
‘A’ama crabs play a crucial role in Hawaii’s coastal ecosystem. They are nature’s cleaning crew, consuming organic debris and helping to keep the shoreline clean.
Physically, ‘A’ama crabs are quite distinctive:
- Color: Usually black, blending with lava rocks
- Size: Up to 5 inches across the carapace
- Shell: Thin and slightly rough
Interestingly, shed ‘A’ama shells appear red. This is because all crabs have a reddish color beneath their outer layer.
Living ‘A’ama crabs have special cells called chromatophores that give them their black coloration.
In Hawaiian culture, these crabs hold significance. Their name “‘A’ama” translates to “to walk with caution,” reflecting their cautious nature and quick movements.
2. Samoan Crab (Mud Crab)
The Samoan crab, also known as the mud crab, is a fascinating crustacean found in Hawaii’s coastal waters.
This large species, scientifically named Scylla serrata, was introduced to Hawaii from Samoa in the 1920s to establish a commercial fishery.
These crabs are notable for their impressive size and adaptability.
They can grow up to 9 inches wide and weigh several pounds.
Samoan crabs have a unique ability to thrive in both freshwater and saltwater environments, making them well-suited to Hawaii’s diverse aquatic ecosystems.
Habitat and behavior:
- Prefer muddy bottoms in brackish water
- Often found near river mouths and mangrove areas
- May burrow in intertidal zones during the day
Fishing regulations in Hawaii protect these crabs:
- Minimum size: 4 inches (carapace length)
- No spearing allowed
- Taking crabs with eggs is prohibited
Samoan crabs are considered a delicacy in Hawaiian cuisine.
However, they are challenging to harvest in large quantities, which has helped maintain their populations.
Most commercially available Samoan crabs in Hawaii are caught as bycatch in other fisheries.
Conservation efforts focus on preserving the habitats of these remarkable crustaceans.
By protecting mangrove areas and maintaining clean river mouths, Hawaii helps ensure the continued presence of Samoan crabs in its waters.
3. Kona Crab (Kuahonu)
Kona crabs, scientifically known as Ranina ranina, are a prized delicacy in Hawaii.
These reddish-orange, squat crabs inhabit the sandy ocean bottom, where they burrow to evade predators.
Also called “spanner crabs” in other parts of the world, Kona crabs are known for their mild flavor.
Culinary enthusiasts often prepare them simply boiled or Chinese-style with ginger, green onions, salt, and white pepper.
In Hawaii, Kona crabs are subject to specific fishing regulations:
- Closed season: May through September
- Minimum size: 4 inches (carapace length)
- Fishing method: No spearing allowed
These regulations help maintain a sustainable population and protect the species during crucial breeding periods.
Kona crabs play a significant role in Hawaii’s commercial fishing industry.
They are one of the main crab species fished commercially in the islands, alongside kuahonu and Samoan crabs.
Eco-conscious consumers can take comfort in knowing that Kona crabs are generally resilient to fishing pressure due to their fecundity and quick maturation.
However, continued monitoring and adherence to fishing regulations are essential for maintaining a healthy population.
4. Blue Swimming Crab
The Blue Swimming Crab, scientifically known as Portunus pelagicus, is a captivating species found in Hawaiian waters.
This crustacean is easily recognizable by its vibrant blue coloration and distinctive paddle-like back legs.
Adult Blue Swimming Crabs typically reach a width of 5 to 7 inches.
Their carapace is adorned with sharp spines along the edges, serving as a defense mechanism against predators.
These crabs are excellent swimmers, using their flattened rear legs to propel themselves through the water with surprising agility.
Their swimming prowess allows them to navigate both shallow coastal areas and deeper offshore waters.
In Hawaii, Blue Swimming Crabs play a vital role in the marine ecosystem.
They are opportunistic feeders, consuming a variety of small fish, mollusks, and plant matter. This dietary flexibility helps maintain balance in their habitat.
The life cycle of these crabs is fascinating. Females can produce up to 2 million eggs at a time, which they carry under their abdomen until hatching.
- Habitat: Sandy or muddy sea floors
- Diet: Small fish, mollusks, algae
- Predators: Large fish, octopuses, humans
Conservation efforts are crucial for protecting Blue Swimming Crab populations.
Sustainable fishing practices and habitat preservation help ensure the continued presence of these beautiful creatures in Hawaii’s marine ecosystems.
5. 7-11 Crab (Spotted Reef Crab)
The Seven-Eleven Crab, scientifically known as Carpilius maculatus, is a striking inhabitant of Hawaii’s coral reefs.
Its distinctive appearance features a light brown or pinkish carapace adorned with vibrant red-brown spots.
These crustaceans can grow up to 7 inches (18 cm) in size, making them easily visible to divers and snorkelers.
Their nickname “Seven-Eleven” comes from the pattern of spots on their shell, typically consisting of 11 large spots.
Spotted Reef Crabs play a crucial role in the reef ecosystem.
They are opportunistic feeders, helping to maintain the balance by consuming various organic matter.
Their diet includes algae, small invertebrates, and detritus.
Despite their appealing appearance, these crabs are not suitable for human consumption.
While some reports have suggested toxicity, scientific testing has found no evidence of paralytic shellfish toxins in their flesh.
Conservation efforts are essential to protect these fascinating creatures.
Snorkelers and divers should observe them from a distance, avoiding handling or disturbing their natural habitat.
By respecting their environment, we can ensure future generations will continue to enjoy the sight of these colorful crabs on Hawaii’s reefs.
6. Black-Clawed Crab
The Black-Clawed Crab, also known as the Black-Fingered Mud Crab, is a fascinating species found in Hawaiian waters.
Its scientific name is Panopeus herbstii, and it belongs to the infraorder Brachyura.
This small crustacean typically grows to about 4 cm in size, making it the largest among mud crabs.
Its most distinctive feature is the pair of black-tipped claws, which are often unequal in size.
The Black-Clawed Crab plays a crucial role in Hawaii’s marine ecosystems.
Like many crab species, it contributes to nutrient cycling and helps maintain the health of its habitat.
Habitat and Behavior:
- Muddy or sandy bottoms
- Mangrove swamps
- Oyster reefs
- Rocky intertidal zones
These crabs are primarily nocturnal, emerging at night to feed on various small marine organisms and detritus.
During the day, they often hide under rocks or in crevices to avoid predators.
Conservation efforts in Hawaii aim to protect the Black-Clawed Crab and its habitat.
Visitors to Hawaiian tidepools and shallow reefs are encouraged to be mindful of their steps and use lookboxes to observe these fascinating creatures without disturbing them.
7. Thin-Shelled Rock Crab (‘A’ama)
The Thin-Shelled Rock Crab, scientifically known as Grapsus tenuicrustatus, is a common sight along Hawaii’s rocky shores.
Locals refer to this agile crustacean as ‘A’ama, a name that echoes through Hawaiian culture and cuisine.
These crabs are easily recognizable by their distinctive appearance.
They sport a carapace that can reach up to 2 inches in width, adorned with vibrant colors that help them blend into their surroundings.
‘A’ama crabs are masters of camouflage, thanks to special cells called chromatophores.
These cells allow the crab to change its coloration, helping it avoid predators and surprise unsuspecting prey.
Found primarily in the splash zone, these crabs are well-adapted to life at the water’s edge.
Their strong legs and claws enable them to navigate rocky terrain with impressive speed and agility.
In Hawaiian ecosystems, ‘A’ama crabs play a vital role. They help maintain the balance of their habitat by feeding on algae and small organisms, contributing to the health of tide pools and shallow reef areas.
Traditionally, Hawaiians have harvested these crabs for food.
Nowadays, conservationists encourage sustainable practices to ensure the continued presence of these fascinating creatures in Hawaii’s coastal landscapes.
8. Sally Lightfoot Crab
The Sally Lightfoot Crab, scientifically known as Grapsus grapsus, is a vibrant and agile crustacean found along the coasts of the Americas.
While not native to Hawaii, this species is worth mentioning due to its striking appearance and unique characteristics.
These crabs are easily recognizable by their bright coloration.
Adult Sally Lightfoot Crabs display vivid red, orange, and blue hues, making them a favorite subject for photographers and nature enthusiasts.
Young Sally Lightfoot Crabs exhibit a different appearance. They are black or dark brown, providing excellent camouflage against the dark lava rocks of their habitat.
The species is known for its remarkable agility. Sally Lightfoot Crabs can quickly navigate rocky shorelines, effortlessly evading predators and waves. This nimbleness has earned them their unique name.
In terms of size, these crabs are relatively modest. Their carapace typically measures just over 8 centimeters in length.
They possess five pairs of legs, with the front pair featuring small, symmetrical claws.
Sally Lightfoot Crabs play an important role in their ecosystem.
They help maintain the cleanliness of their habitat by consuming algae and detritus.
Their presence also contributes to the biodiversity of coastal areas.
While not found in Hawaii, the Sally Lightfoot Crab serves as an excellent example of the diverse and colorful crustacean life that exists in tropical and subtropical coastal regions around the world.
9. Pom-Pom Crab (Boxer Crab)
The pom-pom crab, also known as the boxer crab, is a fascinating species endemic to the Hawaiian Islands.
Its scientific name is Lybia edmondsoni, and it belongs to the family Xanthidae.
These tiny crustaceans have earned their nickname due to their unique behavior.
They carry sea anemones in their claws, resembling cheerleaders with pom-poms or boxers with gloves.
In Hawaiian, the pom-pom crab is called “kūmimi pua,” which translates to “inedible flower crab.”
This name reflects its appearance and local cultural significance.
Pom-pom crabs typically inhabit shallow waters, rarely venturing deeper than 66 feet (20 meters).
They prefer sandy or gravelly sea beds, which provide excellent camouflage for these small creatures.
The relationship between the crab and its anemones is fascinating:
- Crabs use three different species of anemones
- Sometimes they substitute sponges or corals
- This symbiosis isn’t essential for either species’ survival
Pom-pom crabs utilize their anemone “gloves” for both protection and feeding.
The anemones’ stinging cells deter predators, while the crabs can use them to catch small prey.
These unique crustaceans showcase nature’s incredible adaptations and the diverse marine life found in Hawaii’s waters.
10. Hermit Crab
Hawaii is home to several fascinating species of hermit crabs.
These unique crustaceans are known for their habit of inhabiting empty shells for protection.
One notable species is the Hairy Yellow Hermit Crab (Aniculus maximus), which can be spotted in Hawaiian waters.
This colorful creature adds vibrancy to the underwater landscape.
Another interesting variety is the Hazlett’s Hermit Crab (Calcinus hazletti). These small crabs are often found in shallow reef areas, scavenging for food.
Hermit crabs play a crucial role in Hawaii’s marine ecosystems.
They act as natural cleaners, helping to maintain the health of coral reefs and tidepools.
Most hermit crabs in Hawaii are nocturnal, becoming active after dark.
This behavior helps them avoid predators and find food more easily.
Interestingly, some hermit crabs form symbiotic relationships with sea anemones.
The Anemone hermit crab (Dardanus gemmatus) carries anemones on its shell for protection and camouflage.
When visiting Hawaiian beaches or snorkeling in shallow waters, keep an eye out for these fascinating creatures.
Remember to observe them respectfully without disturbing their natural habitat.
11. Snowflake Crab
The Snowflake Crab, scientifically known as Lophozozymus pulchellus, is a stunning crustacean found in the waters surrounding Hawaii.
Its name derives from the intricate white patterns adorning its carapace, reminiscent of delicate snowflakes.
These small crabs typically measure between 1 to 2 inches in width.
Their body color ranges from light brown to reddish-orange, providing a striking contrast to the white markings.
Snowflake Crabs inhabit coral reefs and rocky areas in shallow waters.
They are often spotted scuttling among coral crevices or hiding under rocks during the day, as they are primarily nocturnal creatures.
Key features of the Snowflake Crab include:
- Distinctively patterned carapace
- Strong, sharp claws
- Excellent camouflage abilities
While beautiful, it’s important to note that Snowflake Crabs are not for consumption.
They contain toxins that make them potentially dangerous if ingested.
These crabs play a vital role in the Hawaiian marine ecosystem.
They help maintain reef health by consuming algae and detritus, contributing to the delicate balance of the underwater environment.
Conservation efforts are crucial to protect Snowflake Crabs and their habitats.
Snorkelers and divers should admire these creatures from a distance, avoiding disturbing their natural surroundings.
12. Zebra Crab
The Zebra Hermit Crab, also known as the Hawaiian Reef Hermit, is a fascinating marine creature found in Hawaii’s coastal waters.
Its scientific name is Calcinus laevimanus, and it belongs to the hermit crab family.
These crustaceans are known for their striking appearance.
They feature distinctive white or orange bands on their dark pincers and legs, giving them a zebra-like pattern.
Their eyestalks are a vibrant blue color, fading to orange at the tips.
Zebra Hermit Crabs typically grow to a size of 1 to 1.4 inches, making them relatively small compared to other crab species.
They inhabit the intertidal zones of the Indo-Pacific region, including Hawaii’s reefs.
In the marine aquarium hobby, Zebra Hermit Crabs are highly sought after for their:
- Colorful appearance
- Small size
- Reef-safe behavior
- Algae-eating habits
These crabs play an essential role in reef ecosystems by helping to clean up debris and control algae growth.
They are known for their peaceful nature and can coexist with various other marine species.
13. Mosaic Reef Crab
The mosaic reef crab, scientifically known as Lophozozymus pictor, is a fascinating species found in Hawaiian waters.
This crab belongs to the Xanthidae family, which includes several colorful and intricately patterned crustaceans.
Mosaic reef crabs are easily recognizable by their striking appearance.
Their carapace displays a beautiful mosaic-like pattern, typically featuring a mix of vibrant colors such as red, orange, and white.
Despite their attractive appearance, these crabs carry a dangerous secret.
They are considered one of the most poisonous crabs in the world.
Their toxins are so potent that even cooking doesn’t neutralize them, making them a serious threat if consumed.
In Hawaiian ecosystems, mosaic reef crabs play an important role.
They contribute to the balance of reef environments and serve as prey for some fish species, including humpback red snappers.
For those interested in marine life, it’s crucial to observe these crabs from a safe distance.
While they make for excellent subjects in underwater photography, handling them is strongly discouraged due to their toxic nature.
Conservation efforts in Hawaii often include protecting the habitats of species like the mosaic reef crab.
By preserving reef ecosystems, we ensure the survival of these unique and important creatures for future generations to study and admire.
14. Pillbug Crab (‘Opaelolo)
The Pillbug Crab, known locally as ‘Opaelolo in Hawaiian, is a fascinating crustacean found in the waters around Hawaii.
This unique creature gets its name from its ability to curl into a ball, much like a terrestrial pillbug.
‘Opaelolo crabs are small, typically measuring less than an inch across.
Their compact bodies are covered with a hard exoskeleton that provides protection from predators.
These crabs have a distinctive appearance:
- Round, smooth carapace
- Short, sturdy legs
- Small, retractable claws
- Pale coloration, often with mottled patterns
‘Opaelolo crabs inhabit rocky intertidal zones and shallow coral reefs.
They are well-adapted to their environment, using their ball-like shape to withstand strong waves and hide from potential threats.
While not commonly seen by casual beachgoers, these crabs play an important role in Hawaii’s marine ecosystems.
They feed on algae and small organisms, helping to maintain balance in their habitats.
Conservation efforts are crucial to protect ‘Opaelolo and other native Hawaiian crab species.
Preserving their natural habitats and raising awareness about these unique creatures can help ensure their survival for future generations to appreciate and study.
