The eggs hatch at night , and the larvae swim to the water surface where they drift with the ocean currents , preying on zooplankton . This stage involves three moults and lasts for 15 – 35 days . After the third moult , the juvenile takes on a form closer to the adult , and adopts a benthic lifestyle . The juveniles are rarely seen in the wild , and are poorly known , although they are known to be capable of digging extensive burrows . It is estimated that only 1 larva in every 20 @,@ 000 survives to the benthic phase . When they reach a carapace length of 15 mm ( 0 @.@ 59 in ) , the juveniles leave their burrows and start their adult lives .