Beneath the depths of the ocean lies a realm inhabited by one of the most extraordinary creatures known to science – the Japanese Spider Crab (Macrocheira kaempferi). As enigmatic as it is colossal, this species of marine crab captivates researchers and enthusiasts alike with its unusual appearance.
Inhabiting the Pacific waters around Japan, the Japanese Spider Crab stands as the largest crustacean in the world, boasting a unique body structure and a remarkable set of elongated legs that have earned it the moniker “Spider Crab” due to its resemblance to a spider.
Join us on an exciting journey as we delve into the fascinating world of the Japanese Spider Crab, a true wonder of the deep seas.
Appearance
The crab’s pear-shaped body is dappled orange-and-cream with a cream underside. Its hard exoskeleton protects its internal organs. The spiny carapace, or shell, is broader in front and narrows towards the back. It has a maximum width of 40 centimeters (15.7 inches). Interestingly, females have a wider carapace than males.
The Japanese Spider Crab has ten long and thin legs, their most distinctive feature. Their legs are fragile with weak joints and do not easily bend. Eight of these legs are for walking, allowing them to scuttle across the seabed.
The two front legs, known as chelipeds, are greatly elongated and resemble the legs of a spider, therefore the name “Spider Crab.” These legs may stretch about 3 to 4 meters (9.8 to 13.1 ft) in length, making it the crab with the longest legs. In contrast, females have shorter chelipeds than their walking legs.
It’s not uncommon for Japanese Spider Crabs to lose legs through encounters with predators, such as an octopus or obstacles like trawl nets. These resilient creatures can survive with as few as three walking legs. Remarkably, they can regrow these lost limbs during molting, though it can take some time.
Diet
Japanese Spider Crabs are omnivorous scavengers, preying on dead animals and decaying organic matter. They play a vital role in the environment by cleaning the ocean floor and devouring carrion. They have a highly developed sense of smell, which allows them to recognize and locate prospective food sources.
Their scavenging nature means these crabs are opportunistic feeders that eat a variety of species they come across. Fish, mollusks, crabs, sea urchins, and sea stars may also form part of their diet. They have also been observed feeding on the carcasses of marine megafauna, such as whales.
Japanese Spider Crabs are more active at night when they travel in search of food. Due to their limited mobility, their feeding habits may differ based on their environment and availability of food. Whilst they can’t swim, their long legs enable them to move quickly and help them to stalk live prey.
Their strong pincers help them to smash and break down their meal. The front claws have been uniquely designed for this purpose. The larger claw serves as a crusher for shattering shells and hard exoskeletons of prey items. The smaller claw assists in manipulating and managing their meal, prying open mollusks or even catching small invertebrates.
Plant material augments the diet of Japanese Spider Crabs. They eat a variety of algae, such as kelp and seaweed, which they tear off using their pincers.
Habitat
The Japanese Spider Crab is native to the Pacific waters surrounding Japan and can be found as far south as Taiwan. They are mainly widespread in the country’s southern and southwestern areas. They live in deep-sea habitats at depths ranging between 50 and 600 meters (164 to 1968 ft).
These crabs are benthic, which means they live on or near the ocean floor. They favor rocky and sandy bottoms where they may seek refuge and hide.
Reproduction
The Japanese Spider Crab’s mating season usually lasts from January to March. While their mating behavior remains a mystery, we do know that fertilization is internal. Males store sperm in packets and transfer them to the female’s abdomen using their special front claws.
After laying her eggs, the famel carries them on her underside, using her back legs to keep them oxygenated. A single female can lay a staggering 1.5 million eggs each season, but very few survive to adulthood. These tiny eggs (around 0.63-0.85 mm) hatch after about 10 days. Once hatched, the planktonic larvae are on their own, venturing out into the ocean currents.
Japanese Spider Crab larvae progress through distinct stages: two zoeal stages and a megalopa stage. Interestingly, their zoeal stages are shorter (12-37 days) compared to other crabs in the region. The megalopa stage lasts about 30 days on average.
The ideal water temperature for these larvae is between 15-18°C and likely spend their larval stages in shallower waters before migrating deeper. The first molt, called the prezoeal stage, is a dramatic transformation. The hatchling sheds its skin through a series of contortions and flips, eventually emerging as a tiny crab. Spider Crabs are not known for their parental care habits.
The entire breeding cycle takes roughly a year, though exact timings remain unclear.
Threats
The Japanese Spider Crab faces several threats to its population. Some of these threats include:
- Overfishing as these crabs are considered a delicacy during crab-fishing season
- Habitat destruction due to human activities such as trawling
- Ocean acidification which can dissolve exoskeletons and lead to slow development of larval stages
- Rising sea temperatures due to climate change can negatively affect reproduction and growth
6 Facts About The Japanese Spider Crab
- The Japanese Spider Crabs are also known as “Taka-ashi-gani” in Japanese, which translates to “tall footed crab.”
- Their long legs allow them to move gracefully across the ocean floor.
- Their legs can regenerate after successive molts.
- The largest recorded specimen had a leg span of about 5.5 meters (18 feet).
- They have remarkable lifespans and can live up to 100 years.
- This species is a member of the “decorator crabs” group, which is known to embellish their shells with sponges, plants, and anemones.
FAQs
How much Do Japanese Spider Crabs weigh?
Japanese Spider Crabs are impressive in size, and are the heaviest crab. They can weigh up to 19 kilogram (42 pounds). Despite their large size, they are actually the second heaviest arthropod, coming in behind the American lobster at 20 kilograms (44 pounds).
Are Japanese Spider Crabs dangerous to humans?
Despite their frightening look, Japanese Spider Crabs are typically regarded as gentle and are harmless to humans. They are also sluggish and have very poor eyesight.
Is the Japanese Spider Crab endangered?
The Japanese Spider Crab is not endangered. Unfortunately, there has been a decline in its population in recent years. To combat this, several conservation efforts are underway such as protection during the breeding season and restocking with young crabs raised in controlled environments.
How do Japanese Spider Crabs grow?
Japanese Spider Crabs shed their exoskeleton to grow, leaving it vulnerable to predation. This complex process can take up to two days and is very risky. If they get stuck during molting, it can be fatal. Sometimes even the sheer exertion of shedding their old shell can be so exhausting that some crabs die shortly after.
What eats Japanese Spider crabs?
Due to their large size and tough exoskeleton, adult Japanese spider crabs don’t have many natural threats. When they shed their exoskeleton they are vulnerable to predation from octopuses and large fish.
