How Do Krill Reproduce?
Krill, tiny crustaceans in the family Euphausiids, are the base of the food chain in Antarctic and Arctic seas, constituting one of the largest biomasses of any known species of animal on the planet. Concern is spreading throughout the scientific community about the fishing of krill, which has become popular as a dietary supplement for humans, as well as a staple in fish pellets for fish farming operations. As a result, studies are being conducted into how and in what circumstances krill reproduce.
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When They Breed
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Krill reach sexual maturity after 3 years, and both male and female krill are required to reproduce. During the dark, cold months krill shrink in size and lose their reproductive capacity--a process called "regression." As warmth, hours of light and food supply increases, they become sexually mature again.
How They Mate
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The male produces tiny sperm packets and uses his legs to transfer them to the female's reproductive organs. The female stores the sperm packet in a pouch until she is ready to lay her eggs. The eggs are fertilized while leaving her body.
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Quantity of Spawn
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Krill spawn eggs in several "broods" containing up to 8,000 eggs. Krill may release eggs multiple times per season. The spawning season can last as long as 5 months.
Juvenile Form
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The fertilized eggs sink to just above the continental shelf. After hatching, they live on their yolk reserves, ascending toward the surface in several juvenile stages until phytoplankton becomes available. The first stage is a larva called a nauplius, which has only antennae for swimming and mouthparts. This stage is followed by larval stages called metanauplius, calyptopis and furcilia, with several substages of each. When the larvae's exoskeletons become too small, the larvae molt, growing progressively larger exoskeletons which increase the size of the larvae and add more body segments and appendages.
Importance of Research
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Besides its importance as an economic resource for humans, krill are the mainstay food for several species of whales, penguins and seals, many pelagic birds and uncountable numbers of small fish, crustaceans and other marine life. Some of these creatures are endangered or threatened, so proper management of krill fisheries is paramount. Learning the reproductive patterns of krill may help determine fishing guidelines, or may aid in the creation of krill farms in the future.
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References
- Photo Credit whale shark image by Earl Robbins from Fotolia.com
