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Krill Facts and Its Importance to the Antarctic Ecosystem


Krill are small, shrimp-like crustaceans that are the main food source for many marine animals and fish. Also known as euphausiids, these small invertebrates, or animals without a backbone, are found in oceans all over the world. The name “krill” is a Norwegian word meaning “young fry of fish.” Shrimplike marine invertebrates that grow no bigger than about two and one-half inches (6 cm), krill are nonetheless food for gigantic baleen whales, along with penguins, seals, fish, sea birds, and many other predators. Their scientific name is Euphausia superb.

What do Krill Look Like?

Krill feed on phytoplankton, which are microscopic, single-celled plants that can be found near the ocean’s surface and live off the sun and carbon dioxide. Krill become the main diet of hundreds of different animals, including penguins, seabirds, seals, sharks, squid and many species of whales. If it were not for krill, much of the Antarctic ocean’s life would not exist.

Krill appear pink and opaque, like baby shrimp. Antarctic krill represent the largest of the 85 known krill species. They are estimated to number from 125 million tons to 6 billion tons in the waters around Antarctica. Krill live in diverse environments, from warm, tropical seas to the freezing Antarctic Ocean. During certain seasons, krill congregate in such large and tight swarms that they can be seen from space. Scientists estimate that the total weight of all the Antarctic krill is more than the total weight of all humans on Earth.

As krill are crustaceans, they have a chitinous exoskeleton made up of three segments: the cephalon or head, the thorax and the abdomen. The first two segments are fused together into one segment called the cephalothorax, which is usually transparent. Krill have compound eyes that consist of thousands of individual photoreceptor units. They have two antennae and several pairs of thoracic legs that include the feeding legs and the grooming legs. Krill have five additional legs called “swimmerets” that look like tiny feathers and act as fins to propel the krill through the water.

How Long Do Krill Live?

Antarctic krill have a lifespan of 10 years. During the day, they stay far below the surface in order to avoid their many predators. At night, they drift to the surface in search of phytoplankton. Other species of krill display a different pattern. They tend to swarm near the surface during the day, a phenomenon that has many scientists perplexed as it leaves the krill open prey to the ocean life. Some researchers believe the tides or ocean currents drive krill to the surface during the day; others think that krill swarm at the surface during the day to reach more phytoplankton. Others hypothesize that the warmer waters at the surface are more conducive to reproduction. These swarming behaviors vary by location and specific krill species. When faced with a predator, a swarm will scatter, and some krill will even molt, or shed their external body, instantaneously, leaving it behind as a decoy for the predator.

There are recent studies that point to a decline in the numbers of Antarctic krill by 80 percent since the 1970s. Aside from predation from marine life, commercial fishing of krill is not uncommon. Most of the krill catch is used in the pharmaceutical industry, for aquarium food or as bait in sport fishing. In Russia and Japan, krill are also eaten by humans. Another factor to consider is global warming. As temperatures have risen during the years, Antarctic icehas melted, which affects the krill because they feed on algae found beneath the ice. Experiments to determine the feasibility of producing krill off the coast of California are currently being conducted in an effort to ensure that krill populations remain healthy for the good of all ecosystems.

Why are Krill so Important to the Antarctic Ecosystem?

Krill can be found in abundance in the Antarctic Ocean, which is one of the most remote areas on Earth. The Antarctic Ocean comprises the waters surrounding Antarctica, and is sometimes called the Southern Ocean. Krill are an integral part of the Antarctic’s ecosystem, which is a community of living and nonliving things that work together. In the Antarctic ecosystem, krill feed on phytoplankton, which are microscopic, single-celled plants that can be found near the ocean’s surface and live off the rays of the sun and carbon dioxide. Krill become the main diet of hundreds of different animals, including seabirds, penguins, seals, shark, squid and many species of whales. Due to the sheer numbers of krill, their predators can eat their fill close enough in the food chain to benefit from the phytoplankton before the energy is lost, thereby allowing the Antarctic to support a wide population of large animals. If it were not for krill, much of the Antarctic’s ocean life would not exist.

Krill appear pink and opaque, like baby shrimp. Antarctic krill represent the largest of the 85 known krill species. They are estimated to number from 125 million tons to 6 billion tons in the waters around Antarctica. Krill live in diverse environments, from warm, tropical seas to the freezing Antarctic Ocean. During certain seasons, krill congregate in such large and tight swarms that they can be seen from space. Scientists estimate that the total weight of all the Antarctic krill is more than the total weight of all humans on Earth.

Antarctic krill have a lifespan up to 10 years. During the day, they stay far below the surface in an effort to avoid their many predators. At night, they drift to the surface in search of phytoplankton. Other species of krill display a different pattern. They tend to swarm near the surface during the day, a phenomenon that has many scientists perplexed as it leaves the krill open prey to the ocean life. Some researchers believe that tides or ocean currents drive krill to the surface during the day; others think that krill swarm at the surface during the day to reach more phytoplankton. Others hypothesize that the warmer waters at the surface are more conducive to reproduction. These swarming behaviors vary by location and exact krill species. When faced with a predator, a swarm will scatter, and some krill will even molt, or shed their external body, instantaneously, leaving it behind as a decoy for the predator.

There are recent studies that point to the decline in the numbers of Antarctic krill by 80 percent since the 1970s. Aside from predation from marine life, commercial fishing of krill is not uncommon. Most of the krill catch is used in the pharmaceutical industry, for aquarium food or as bait in sport fishing. In Japan and Russia, krill are also eaten by humans. Another factor to consider is global warming. As temperatures have risen over the years, Antarctic sea icehas melted, which affects the krill because they feed on algae beneath the ice. Experimental fishing to determine the feasibility of producing krill off the coast of California is currently being conducted in an effort to ensure that krill populations remain healthy for the well-being of all ecosystems.

How do Krill Reproduce?

Krill can only reproduce when they have an abundance of food. The male krill produce sperm packets which they transfer with their legs to the openings in the reproductive organs of the female krill. The females keep these sperm packets in a pouch until it is time for them to lay their eggs. Then, when the eggs leave her body they are fertilized externally.

The female krill lay their eggs in the summer. Each female can lay up to 10,000 eggs at a single time. Then they are able to lay eggs again a few times during each spawning season. The spawning occurs near the ocean’s surface. After the eggs have been fertilized, they sink down as far as 2,000 meters to the bottom of the ocean until they are ready to hatch. Then, after the eggs hatch and the larvae appear, they make their way up to the surface again, where the larvae start to feed.

The krill hatch from eggs which are free floating. When the eggs hatch, the baby krill larvae pass through several stages in which they molt. This means that they cast off their hard outer skeletons which prevent them from growing bigger. After each molt, the young krill grow bigger and develop more appendages and segments until they become adult krill. This happens over a period of a few months. First they appear as larvae with simple antennae, known as antennules, which they use to swim with. Then the larvae develop thoracic limbs for better swimming. During the time that the new skeleton remains soft, the krill continue to grow and develop. When krill are fully grown, they are able to shrink in size after each molt. They do this if they cannot find enough food. Then when food becomes plentiful once again, they can increase in size.

After the summer mating season is over, adult krill lose their distinctive male and female sexual characteristics and resemble juvenile krill. The next springthey regain their sexual characteristics once again in order to be ready for the next mating season the following summer. Different species of krill live between two and ten years.

Scientists have found that swarms of krill swim on the surface of the ocean during the day. They hypothesize that the tides and ocean currents might be partly responsible for this behavior, and also that phytoplankton is denser and more available at the surface. They also suggest that at the surface where the water is warmer the conditions for reproduction are increased. The reason for this is that when the female krill releases her eggs at the warmer surface of the ocean, the incubation time for the eggs is speeded up and they can develop more quickly. And if the young krill are produced more quickly, the time they are exposed to predators is reduced. Also when the larvae hatch near the surface of the ocean they are in a place where there is more food available and thus their chances of survival become greater as well.

Global warming has led to climate change in Antarctica. With temperatures getting warmer over the last 30 years, there is a reduced surface of sea ice, which the krill need to survive, and this has led to a shortened season of krill spawning and consequently a reduction in the rate at which krill reproduce. Since the krill population is so important to maintaining the ecosystem in Antarctica, the conservation and preservation of krill has become an issue of increasing concern to environmentalists.