Mangrove Horseshoe Crab - Mating Biology

Mating Biology

In the spring, horseshoe crabs migrate from the deeper water to the shallow, muddy areas. Nesting usually follows the cycle of the high tide of the full and new moons. During the mating period, the males will follow and cling to the backs of their potential mates using modified prosomal appendages for long periods of time before the egg-laying has occurred. Horseshoe crab species with low spawning densities and 1:1 sex ratios, such as the mangrove horseshoe crab, are found to be monogamous. In addition, the female does not choose her mate. Males find their female mates with the use of visual and chemoreceptive signals. Once a mate is found, the female digs a hole and lays the eggs while the male externally fertilizes them. Once the eggs are laid, the male and female head back to the ocean, and the eggs develop on their own. Their eggs are large, and after a couple weeks, the eggs hatch into miniature versions of the adults.

Mangrove horseshoe crabs in Singapore breed from August to April. Juveniles grow about 33% bigger each time they moult, and it takes the juveniles about five moults to grow from 2 centimetres (0.79 in) to adult size.