Many species, including crabs, undergo long-distance migrations in order to release offspring in areas favorable for proper early development. The risks associated with migrating can be costly, including acquiring and allocating energy for both migration and oogenesis (egg development) and increased predatory risk. Two of the most spectacular migrations of crabs are blue crab migration at Chesapeake Bay and red crab migration Chrismas Island. However, blue and red crabs choose different strategies (e.g. timing, route, mechanisms) in order to successfully complete migration and maximize survival of offspring.
At Chesapeake Bay, blue crab mating typically occurs from May to ...view middle of the document...
Furthermore, prior research has indicated that after mating female blue crabs fed extensively in the early summer months, first allocating energy to muscle growth, then to egg development and hepatopancreas reserves. This would enable crabs to build muscle mass required for long-distance migration and produce eggs en route to the spawning grounds.
Another spectacular crab migration is the red crab migration at Christmas Island, South Indonesia. At the beginning of the wet season (usually October / November), most adult red crabs suddenly begin a spectacular migration from the forest to the coast to breed. Breeding is usually synchronized island-wide. The rains provide moist overcast conditions for crabs to make their long and difficult journey to the sea.
During peak migration times, sections of roads where crabs cross in high numbers may be closed to vehicles for short periods of time. While the rains provide the moist preconditions for the march to begin, the timing of the migration breeding sequence is also linked to the phases of the moon. Eggs are released by the female red crabs into the sea precisely at the turn of the high tide during the last lunar quarter. The sea level at the base of the cliffs and on the beaches, where the females release their eggs, at this time varies the least for a longer period, and it is therefore safer for the females approaching the water's edge to release their eggs.
Males lead the first wave of the downward migration and are joined by females as they progress. Larger males arrive at the sea first (after about five to seven days) but are soon outnumbered by females. The crabs replenish moisture by dipping in the sea. The males then retreat to the lower terraces to dig burrows. The density of burrows is high (one to two per square meter) and males fight each other for burrow possession. The females move to the terraces and mating occurs. After mating, males dip again and begin returning inland. The females produce eggs within three days...