Reproduction only takes place where food is abundant; eggs are rich in lipids. Male krill produce spermatophores, which they transfer to the female using the uppermost abdominal appendages. The sperm is stored by the female and later released for fertilization as the eggs pass out of the genital opening. Females may spawn several times during the season, each brood consisting of thousands of free-floating eggs. Spawning occurs near the surface. The higher temperature of the shallow water allows faster development of the eggs, thereby limiting exposure to predators, and ensures that the offspring hatch into a food-rich environment.
After hatching as larvae, krill mature through juvenile stages (called nauplius, protozoea, zoea, and cyrtopia) into the adult form over a period of a few months, with segments and appendages as well as growth added at new molts.
Adult krill shed their sexual characteristics after the summer spawning season, and return to a juvenile-like state. They mature again in the spring. The krill lifespan is between two and 10 years, depending on the species.
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