Red king crab

The red king crab is very large.

It lives in cold ocean water. It likes to stay in the deep sea.

Female crabs stay in warmer water. This helps their eggs get ready to hatch. Males stay in colder water to save energy.

These crabs have five sets of gills. They use the gills to breathe. The gills take in the air from the water.

Some people catch these crabs for food. They are very expensive to buy.

It is a very big animal.

The red king crab is a very large crab.

It lives in cold waters in the North Pacific Ocean. These crabs can have a leg span of 1.3 meters.

They are named for the color they turn when cooked. In the wild, they are often a dark burgundy color.

Most crabs live in deep, dark water. They like to stay on the sand or mud.

Tiny baby crabs stay in shallow water for safety. When they are two years old, they move deep.

Female crabs need warmer water for their eggs. This helps the eggs get ready to hatch. Males stay in colder water to save power.

Crabs use gills to breathe underwater. They have five sets of gills inside their shell. A small part called a scaphognathite moves to pull water over the gills. This lets the crab take in oxygen. They also have an open circulatory system. This means their blood flows freely through their body parts.

The red king crab is a very large creature from the ocean.

It is the biggest kind of king crab in the world. These crabs live in cold waters in the North Pacific Ocean. They can be found near the Bering Sea and the Gulf of Alaska. They can even be found in the Sea of Japan. A single crab can have a leg span of 1.3 meters.

They are called red king crabs because of how they look when cooked. In the wild, they are actually a dark burgundy color.

These crabs have a very interesting way of living.

Tiny baby crabs, called zoea larvae, stay in shallow water. This is where they find plenty of food and protection. When they are two years old, they move to much deeper water. They often live on the sand or mud at the bottom. In the summer, they stay in deep water. In the winter or early spring, they move to shallow water to mate. They often gather in large groups called podding.

Humans have moved these crabs to new places.

In the 1960s, the Soviet Union wanted a new type of catch for Europe. They tried to move crabs to the Murmansk Fjord in the Barents Sea. The first group did not survive the trip by land. However, a second group was flown in and survived. These crabs spread quickly and were found in Norway by 1977. Some people in Norway call them "Stalin's crabs." They are now an invasive species in that area.

Red king crabs are very important to the fishing industry.

They are the most expensive king crab for people to buy. Most of them are caught in the Bering Sea and Norton Sound, Alaska. However, their numbers are going down in some places. Scientists think this might be because of overfishing or warmer water. In Norway, fishing is managed by special rules. Only 259 Norwegian fishermen were allowed to catch them in 2006.

This helps keep the population under control.

Inside their bodies, crabs have special ways to breathe and move blood.

They have five sets of gills inside a hard shell called a carapace. A small part called a scaphognathite moves to pull water over the gills. This helps them take in oxygen from the water. They also have an open circulatory system. This means their blood flows somewhat freely around their body parts. A heart helps push this fluid through the body. The heart is controlled by a group of nerve cells. This keeps the crab's body working well.

The red king crab, known scientifically as *Paralithodes camtschaticus*, is the largest species of king crab in the world.

These massive crustaceans are native to the cold waters of the North Pacific Ocean. They live in areas ranging from the Bering Sea to the Gulf of Alaska. You can also find them in the Sea of Okhotsk and the Sea of Japan. They are highly valued by humans and are heavily targeted by commercial fisheries. While they are named "red" king crabs, this refers to the color they turn when cooked. In their natural habitat, living crabs tend to be a dark burgundy color.

These crabs have a complex life cycle that involves moving between different ocean depths.

It begins with the zoea larvae, which are newly hatched crabs. These tiny larvae stay in shallow waters where food is plentiful and protection is easier to find. Once they reach about two years of age, the crabs move to much deeper water. They typically live on sand or muddy areas of the ocean floor. During the summer, they stay in deep water below the summer thermocline, which is a layer of water where temperature changes quickly. In the winter or early spring, they migrate back to shallower depths for mating. During these times, hundreds of crabs may gather in tight, concentrated groups known as podding.

Temperature plays a vital role in how these crabs behave and grow.

Mature females must stay in warmer water, near 4°C, to ensure their eggs are ready for hatching. In contrast, males stay in relatively cold water, near 1°C, to conserve their energy. The crabs can tolerate a wide range of temperatures, but extreme cold can slow their growth. If the water temperature falls below 0°C, their growth and molting processes become very slow. They molt most quickly when the water is around 10°C. They also have a high capacity to adapt to different salinity levels, though juveniles are better at regulating their internal salt levels than adults.

Humans have significantly changed where these crabs live through intentional introduction.

In the 1960s, the Soviet Union wanted to provide a valuable new catch for Europe. They attempted to move crabs to the Murmansk Fjord in the Barents Sea. An initial attempt to move them overland failed, but a second group was flown in and survived. These crabs successfully bred and spread throughout the Barents Sea. By 1977, they were found in Norway, where some call them "Stalin's crabs." In this region, they are considered an invasive species. They spread rapidly along the Norwegian coast, sometimes advancing about one kilometer per year. Scientists worry they might reach important cod breeding grounds near Lofoten.

Because they are so large, red king crabs are a major part of the global seafood industry.

They are the most expensive king crab species per unit weight. Most of the commercial catch comes from the Bering Sea and Norton Sound in Alaska. However, populations in their native far east coastal waters are experiencing a steady decline. Scientists have proposed several reasons for this, including overfishing, warmer ocean waters, and increased predation by fish. Even with fishing controls set by the United States in the 1980s and 2000s, the decline has continued. In Norway, the population is managed through diplomatic agreements between Norway and Russia. As of May 2006, only 259 Norwegian fishermen were permitted to catch them east of the North Cape.

Inside the crab, specialized systems allow them to breathe and move nutrients.

They use five sets of gills located within branchial chambers inside their carapace. A small appendage called a scaphognathite moves back and forth to pull water over these gills. This creates a U-shaped flow of water that allows for gas exchange. To move oxygenated blood, the crab uses an open circulatory system. This means the blood flows somewhat freely among the tissues rather than staying inside vessels. A neurogenic heart, which is controlled by nervous tissue, pumps this fluid. A cluster of nine neurons called the cardiac ganglion helps initiate these heartbeats.

Even the parts of the crab that humans do not eat are scientifically interesting.

When crabs are processed, about 69% of the total mass is considered waste. A large part of this waste is the carapace and the entrails. One specific organ, the hepatopancreas, makes up about 90% of the intestines. This organ is a valuable source of various enzymes, such as protease and lipase. These enzymes are used in many different industrial processes. This shows that every part of the red king crab, from its massive legs to its internal organs, plays a role in its biology and its relationship with the world.