Information on Krill
Called a "keystone" species of its ocean ecosystem, each individual krill weighs only 1 to 2 grams. Cumulatively, they make up one of the largest biomass of any animal species on the planet. Besides ocean-living animals, they are also fished by humans, a practice which, if not carefully managed, could be devastating for the creatures who depend upon krill for food.
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Biology
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Krill are two families of eucarid crustaceans. Bentheuphausiidae consists of Bentheuphausia amblyops, a deep-water krill species found in the North Atlantic which, unlike krill in the Euphausiidae, is not bioluminescent. The Euphausiidae family contains 89 krill species. The most common is Euphausia superba, found in the Antarctic. Other species are found in the Pacific Ocean, Indian Ocean, the Gulf of Oman and east of Sri Lanka. Krill have a calcified exoskeleton divided into three segments: the cephalon, thorax and abdomen. The head and thorax are fused into a cephalothorax. The head has five segments, the thorax has eight, the tail six. Most krill are filter feeders consuming phytoplankton and zooplankton.
Spawning
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Krill become sexually mature after three years, and both genders are required for reproduction. During the darkest, coldest months of the year, krill shrink and lose their reproductive capacity through a process called "regression." As light, warmth and food supply increases, the krill become sexually mature again. A sexually mature male will produce tiny sperm packets, which he transfers to the opening of the female's reproductive organs with his legs. The eggs are fertilized upon leaving the female's body. Krill spawn several "broods," which can contain up to 8,000 eggs. They can release multiple broods per season, which lasts for up to five months.
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Life Cycle
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After being released from the female's body, the fertilized eggs sink hundreds of feet to the continental shelf to hatch. They will live off their yolk reserves as they ascend to the surface until phytoplankton becomes available. The first of many larval stages is called a nauplius. The nauplius have only antennae for swimming and rudimentary mouthparts. This is followed by larval stages called metanauplius, calyptopis and furcilia. Each larval stage has several substages. Each time the larvae's exoskeletons become too tight, the larvae molt. With each molt, the larva grows a progressively larger exoskeleton and adds more body segments and appendages.
Importance to Ecosystem
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Krill is the primary food for many species of whales, including the endangered blue whale and humpback whale. Minke whales and baleen whales depend on krill for food. The Adilie penguin, emperor penguin and rockhopper penguin, crabeater seal, leopard seal and Weddell seal survive on krill and on the fish that eat krill. If fish, seals and penguins can't get enough krill, this will affect apex predators such as killer whales that eat the penguins and seals. Countless pelagic birds such as the endangered black-browed albatross, like the Antarctic petrel and snow petrel eat fish that eat krill. These birds may fly hundreds of miles in search of krill masses. Numerous small fish, crustaceans and other marine life feed on krill.
Importance to Humans
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Krill is being fished by humans who harvest the krill to make krill oil, which is rich in omega-3 fatty acids. Krill oil is used in dietary supplements. Krill is also ground up and used in feed for fish farms. Krill's natural predators are forced to compete with industrial trawling vessels near their hunting grounds and rookeries, disturbing the animals' natural behavior. Several marine species harvested for human consumption, like salmon, squid and rockfish, depend on krill for food. Depleting the waters of krill will negatively affect these fisheries.
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References
- Photo Credit humpback whale,humpback,whale,adolescent,mammal,ma image by Earl Robbins from Fotolia.com
