Krill are small crustaceans that resemble miniature shrimp, growing to about two inches in length. They are incredibly abundant, particularly in the cold waters of the polar regions. These tiny organisms form immense swarms that can span miles, making them visible even from space. Krill represent a foundational element in these marine environments due to their sheer biomass, which is estimated to be larger than that of humans.
Primary Food Sources
The primary food source for most krill species is phytoplankton, which are microscopic marine algae. Phytoplankton are abundant in oceans worldwide and are a foundational part of the marine food web. These tiny plant-like organisms convert sunlight into energy through photosynthesis, making them primary producers.
Krill specifically favor diatoms, a type of phytoplankton, which are plentiful in cold, nutrient-rich waters. Diatoms are highly nutritious for krill, providing the fatty acids necessary for their growth and reproduction. While primarily herbivorous, krill can also consume other small organisms like copepods and fish larvae, or even detritus.
Diverse Feeding Behaviors
Krill are primarily filter feeders, a method where they strain microscopic food particles from the water. They possess specialized comb-like appendages called thoracopods, which interlock to form a basket-like structure. As krill swim, they create a current that draws water through this “feeding basket,” trapping phytoplankton and other small particles while allowing water to pass through.
Beyond filter feeding in the open water, krill exhibit adaptable feeding behaviors. They can graze on algae that grow on the underside of sea ice, known as ice algae. This provides an alternative food source. Krill can also scavenge on detritus, which includes decaying organic matter.
The Ocean Environment and Krill Diet
The specific characteristics of polar ocean environments influence the krill diet. Regions like the Southern Ocean and Arctic Ocean provide ideal conditions for the proliferation of their primary food sources. Nutrient upwelling, where deep, nutrient-rich waters rise to the surface, supports extensive phytoplankton growth.
Sunlight availability is another factor, as it is necessary for the photosynthesis of phytoplankton. Seasonal variations, such as the extended daylight hours in polar summers, lead to phytoplankton blooms. Ice formation also plays a role, as the underside of sea ice offers a stable substrate for ice algae to grow, serving as a supplementary food source for krill.
Krill’s Pivotal Role in the Marine Food Web
The diet of krill is central to the broader marine food web. By consuming large quantities of microscopic phytoplankton, krill act as an important intermediary, converting this energy into a form accessible to larger animals. They effectively transfer energy from the lowest trophic levels to higher ones.
Numerous marine predators depend heavily on krill for sustenance. Whales, including baleen whales like blue whales, consume tons of krill daily. Seals, penguins, and various fish species also rely on krill as a major component of their diet. This makes krill a central component of polar ecosystems, supporting a wide array of marine life.