According to the Great Barrier Reef Marine Park Authority, crustaceans reproduce through externally fertilized eggs. Female crustaceans produce eggs in their ovaries. Males fertilize the eggs after they leave the female's body. The gestational period varies by species. Tiny crustacean larvae fend for themselves from the time of their birth.
The Great Barrier Marine Park Authority explains that some crustacean species release their eggs directly into the water and leave them. Others carry the fertilized eggs in a "brood pouch," carry the eggs with one pair of their limbs or drag them along with a string attached to an egg sac. Parasitic Branchiura, or fish lice, glue their eggs to rocks and buried detritus.
The most unusual aspect of crustacean reproduction is the ability of some species to change gender. According to the University of Edinburgh, other crustaceans practice parthenogenesis. Females of these species produce and fertilize their own eggs without male involvement.
Crustaceans do not grow steadily as they mature because their hard exoskeletons prevent this. Juveniles undergo a series of molts, during which they shed their exoskeletons and develop new ones. The new exoskeletons are initially soft, and during that period the crustaceans grow.
The Great Barrier Reef Marine Park Authority states that a crustacean's primary defense is its bony exoskeleton. Consequently, the animals are extremely vulnerable during each growth phase. Crustaceans typically hide until their new exoskeletons have hardened.