Crabs are amazing creatures that have survived for millions of years thanks to their fascinating and complex reproductive behaviors. As someone who loves marine biology, I wanted to take a deep dive into understanding exactly how crabs reproduce. In this article, we’ll look at the step-by-step process of crab reproduction, from attracting a mate to fertilizing eggs.
The Molting Process
Before crabs can mate, they must first molt, or shed their hard outer shell. This molting process allows the crab to grow larger after they emerge with a new soft shell. Molting also enables female crabs to mate, as their shells must be soft in order to successfully receive sperm from males.
During molting, crabs hide away to avoid being eaten by predators Once their new shell begins to harden after a few days, crabs emerge and are ready to begin the mating process Both male and female crabs molt, but females molt less frequently than males.
Finding a Mate
Male and female crabs attract each other using pheromones, which are natural chemical scents. According to marine biologist Pamela Jensen, male crabs will fan these pheromone scents toward females to get their attention.
Some species like the Dungeness crab have females that release the pheromones instead, signaling they are ready to mate. Blue crabs are known for their ritual of males waving their claws side-to-side to spread their scent toward potential mates.
Mating Embrace
Once males and females have found each other through these chemical signals, the next step is a mating embrace that can last several days. The male crab will tightly grip the female using his claws and legs.
For some species, the female allows this embrace willingly. For others, the male has to prove his strength before the female stops resisting. This extended embrace gives the male time to insert his sperm into the female’s sperm storage organ once she molts.
Copulation
After the female crab molts and is ready to mate, the male will transfer sperm using his gonopods to her gonopores (sexual organs). He deposits the sperm into pouches inside her body called spermathecae where they will be stored until the eggs are ready to be fertilized.
Crabs can mate in a standing position facing each other, but most prefer the male crab to be on top of the female. Once finished, the male will stay with the female protecting her vulnerable soft shell for a few days before going off in search of a new mate.
Fertilizing Eggs
Female crabs don’t fertilize their eggs immediately after mating. The sperm can be stored inside their bodies for up to two years before being used to fertilize multiple batches of eggs. When the female is ready, thousands of eggs will move through her reproductive tract, becoming fertilized by the stored sperm.
Caring for Eggs
Once fertilized, the eggs remain attached under the female crab’s abdomen for several weeks. To care for the 100,000 to 200,000 eggs, female crabs will find a safe spot in the ocean to hide. Some even migrate hundreds of miles to ensure their eggs hatch in an ideal nursery ground.
The eggs are cradled in a spongy substance that keeps them safely in place until they are ready to hatch into tiny larvae. Unfortunately, most of the eggs don’t survive to adulthood due to predators. But the female crab’s dedication in migrating and protecting her eggs helps give them a fighting chance.
From Larvae to Adult
After hatching, the tiny crab larvae will float in the ocean’s plankton while they continue developing over several molt cycles. Once large enough, the juvenile crab will settle to the seafloor, taking on a crab-like form. Several more molts happen over 2-3 years before the crab finally reaches sexual maturity.
Unique Crab Reproduction
While most crabs reproduce using this mating process, there are a few unique exceptions. Certain crab species like porcelain crabs are hermaphrodites, meaning they have both male and female reproductive organs. This allows them to fertilize their own eggs without requiring a mate.
There are also parasitic barnacles that will change the body and behavior of some male crabs, effectively turning them into females for breeding. This bizarre alteration benefits the barnacles since their larvae can then infiltrate the crab’s fertilized eggs.
The reproduction process of crabs is intricate and fascinating. Their ability to store sperm for years before fertilizing eggs allows crabs to breed multiple times. The mating embrace ritual and pheromone signaling add complexity and interest to their courtship behaviors. While not all crabs survive the journey from egg to adulthood, their unique reproductive strategies give this ancient species the diversity and resiliency to thrive.
The Dungeness Crab Habitat
The Dungeness crab has been commercially harvested since the 1800’s and is a common species found along the coast of California all the way up to the Gulf of Alaska and is particularly popular in the states of Oregon and Washington.
Since adult crabs typically live and swim solo and not with a “pack” or family, they tend to find protection while burying themselves in trenches about a meter deep and don’t go out into very deep waters. They might stay close to other crabs not in their family to protect themselves from predators. Juvenile crabs, on the other hand, prefer cooler and more shallow waters than adults and hang out in plants and eelgrass (National Park Service).
Mating occurs during the spring and summer months when females naturally molt.
When female live Dungeness crabs are ready to molt, they shed their exoskeleton to allow them to grow and develop a bigger shell; before this new, hard shell has formed is prime time for mating. The females will release pheromones, or their special chemical scent, to attempt to attract close-by males. When their scent peaks a male’s interest, he will run up on her and literally “hug” her.
Things get a little weird after that! The male Dungeness crab “embraces” the female (sometimes willingly, other times forced) and this can last up to a few days. The female is able to see how strong and worthy her potential mate is and gets to decide whether or not he is the right partner to reproduce with. Usually, the male will carry her off into the distance to hide themselves from predators and other male crabs who probably also smell her pheromones.
Now it’s time to get it on!
The experts at Live Science describe it perfectly–technical terms and all:
“The male transfers sperm by inserting his gonopods (sexual organs resembling antennae) into the two genital pores, called gonophores, on the females underside. The female stores the sperm in a storage sac called a spermatheca until she is ready to use it. Some crabs will mate standing up, facing one another, but most species actually prefer the missionary position, with the female beneath the male. Once copulation is complete, the male will guard the female for a few days (giving her shell time to harden) before taking off in search of a new mate.”
That’s it, folks! Nothing to see here…
Dungeness Crab Babies
Now that the male has moved on, the female needs to produce her eggs and fertilize them with the stored sperm when she is ready. Typically a female Dungeness crab holds onto her eggs to incubate them for 3 to 5 months. In the meantime, she hunkers down in the sand to wait out the chilly winter weather.
A large female can carry up to 2.5 million eggs! The number of babies that are successfully born alive depend on the weather, predators, and how many make it to the hatching stage. Once they are born, baby crabs go through 4 larval stages until they are considered an adult crab, which is the 5th stage.
- Egg Stage: They’re just chilling in their eggs, waiting to be hatched.
- Zoea Larva: In this stage, Dungeness crabs look similar to little shrimp and have a spine that protrudes its head to protect it from predators.
- Megalops Larva: The baby is now taking on more of a crab-type look.
- Juvenile: These little fellows are still so tiny (only about the size of a dime) and vulnerable to the open ocean. They tend to settle on the bottom of the ocean floor and molt several times, while growing, before becoming an adult crab.
- Mature Adult: This Dungeness crab no longer has an attitude toward its mother and can come and go as it pleases. Actually, a mature adult crab is only about 2 years old and does not become an official adult until it goes through about 10 molts. It is now ready to go find a mate and start this cycle all over again!
Mating Crabs
FAQ
How do crabs mate?
Crab mating involves a complex process where males transfer sperm to females, often after a molting period. Many crab species mate after the female molts, when her shell is still soft, and the male will often guard her until her new shell hardens.
Does a crab give birth or lay eggs?
The female can retain sperm for a year or more before extruding eggs. This allows crabs mating in fall or winter to wait until warmer weather to hatch their eggs. Eggs are fertilized as they pass out of the crab’s body and are deposited under the apron.
How long is a female crab pregnant?
155 Likes, TikTok video from New England Science & Sailing (@nescienceandsailing): “We found 2 pregnant blue crabs! Female blue crabs carry their eggs outside their body on their abdomen for about 2 weeks before releasing them into the water to hatch. These sacs (known as their sponge) can hatch anywhere from 750.
What is the yellow stuff in female crabs?
Tomalley is the hepatopancreas (the organ that fulfills the functions of both the liver and the pancreas) of a lobster, crab or other crustacean when used for culinary purposes.
How do crabs reproduce?
Crabs reproduce sexually, meaning two individuals (male and female) contribute genetic material to create offspring. This type of reproduction involves the fusion of specialized sex cells called gametes, which are sperm from the male and eggs from the female.
How do crabs develop eggs?
Crabs go through a fascinating egg development process before they hatch. Understanding this process offers insight into the life cycle of crabs and their ecological significance. During mating, the male crab transfers sperm to the female. Fertilization occurs externally, where the female carries the sperm until her eggs develop.
How do humans affect crab reproduction?
As humans build along coastlines, they often disrupt or destroy the sandy beaches and estuaries where many crab species lay their eggs. Without these crucial breeding grounds, it becomes challenging for crabs to reproduce successfully. Climate change induced by human activities is another factor that influences crab reproduction.
Do crabs synchronize their reproductive cycles?
Some crabs are known to synchronize their reproductive cycles with lunar phases or seasonal shifts. Female crabs typically produce eggs shortly after mating. However, these are not immediately laid; instead, they are stored internally while they are fertilized by the male’s sperm.
How do crabs fertilize their eggs?
The crab egg fertilization process is key to crab survival. It starts right after mating, when the male puts sperm into the female’s body. This ensures the eggs can be fertilized well. During mating, the male crab uses his gonopods to put sperm directly into the female. The sperm stays in her body until it’s time to fertilize the eggs.
Do crabs lay eggs after mating?
Female crabs typically produce eggs shortly after mating. However, these are not immediately laid; instead, they are stored internally while they are fertilized by the male’s sperm. Once fertilization occurs, the female deposits her eggs in a specially designed brood pouch located on her abdomen, where they remain until hatching time.