How do Japanese Spider crabs reproduce?

The mating season for Japanese Spider Crabs (Macrocheira kaempferi) occurs annually, usually from late winter to early spring. Here is a general overview of their reproductive process:

1. Mating Behavior:

- Mature male and female Japanese Spider Crabs come together during the mating period.

- The male spider crab initiates the mating process by approaching the female and grasping her with his legs.

- He carries the female on his back, holding her securely with his strong limbs.

2. Mating Position:

- The male spider crab positions the female in an inverted position, so her ventral (underside) is facing upwards. This positioning facilitates the transfer of sperm.

3. Sperm Transfer:

- The male spider crab uses specialized appendages called pleopods on the underside of his abdomen to transfer sperm packets (called spermatophores) to the female.

- The female receives the spermatophores through specialized openings called thelyca.

4. Sperm Storage:

- After receiving the spermatophores from the male, the female stores them inside specialized storage structures called seminal receptacles or spermathecae.

- The stored sperm can remain viable for a prolonged period, ensuring the female can fertilize her eggs later when they are ready to be laid.

5. Egg Production:

- After mating, the female Japanese Spider Crab undergoes a process of internal fertilization.

- The stored sperm from the male fertilizes the female's eggs within her body.

6. Hatching:

- The fertilized eggs develop and hatch into tiny larvae called zoeae.

- These zoeae larvae are planktonic, meaning they float freely in the water column, drifting with ocean currents.

7. Larval Development:

- The zoeae larvae go through several molting stages and develop into different larval forms, including phyllosoma larvae.

- During their planktonic phase, the larvae feed on microscopic plankton and other organic matter in the water.

8. Metamorphosis:

- After a series of molts and developmental stages, the larvae undergo a metamorphosis and transform into juvenile spider crabs.

- The juvenile crabs then settle down to the ocean floor and begin their benthic lifestyle.

9. Growth and Maturity:

- As the juvenile spider crabs grow, they continue to molt multiple times, shedding their exoskeletons to accommodate their increasing size.

- They gradually reach sexual maturity over the course of several years, eventually becoming adults capable of reproducing.

In summary, the reproductive process of Japanese Spider Crabs involves mating, transfer of spermatophores, internal fertilization, larval development, metamorphosis, and growth to maturity. Their reproductive behavior and larval stages play crucial roles in the species' survival and dispersal within their marine habitats.