Marine food webs are intricate systems where species interact through feeding relationships. At the base of many of these webs are tiny, shrimp-like crustaceans known as krill, which serve as a food source for a variety of marine life. This prompts questions about the role of small fish in these ecosystems, specifically whether they consume krill.
Krill: Tiny Powerhouses of the Ocean
Krill are small, marine crustaceans, resembling miniature shrimp, found in all oceans. While there are 85 known species, the Antarctic krill (Euphausia superba) is notable for its vast biomass. These organisms typically measure up to 6 centimeters (2.4 inches) in length. Krill often congregate in massive swarms, especially in polar waters.
Krill primarily feed on microscopic plants called phytoplankton, using filter-feeding. They convert this energy into a form consumable by larger animals, establishing them as a foundational link in marine food chains. Their abundance makes them a significant food source for many marine animals, including various fish species, whales, seals, penguins, and seabirds.
Defining “Small Fish” and Their Feeding Habits
The term “small fish” encompasses a diverse array of marine species, including adult fish that remain small and the juvenile stages of larger fish. These fish occupy various niches within marine ecosystems, from coastal waters to the open ocean. Their feeding habits are highly varied, reflecting the wide range of available prey and different foraging strategies.
Many small fish are planktivores, feeding on plankton (microscopic plants and tiny animals). Some graze on algae or detritus, while others are active hunters, pursuing smaller invertebrates or fish larvae. The specific diet of a small fish depends on its species, life stage, habitat, and food availability. Different feeding mechanisms, such as suction feeding or ram feeding, are employed depending on the target.
The Specifics: Do Small Fish Consume Krill?
The question of whether small fish consume krill has a nuanced answer, as it depends on several ecological and physiological factors. While krill are a food source for many marine animals, including various fish, the interaction with what is generally considered “small fish” is not universal. Larval and juvenile stages of some fish do consume krill, and krill can be a main food source for certain adult fish.
Size compatibility is a primary factor. Krill, particularly larger species like Antarctic krill, can measure up to 6 cm, which may be too large for many truly small fish. However, smaller krill species or their larval stages are consumed. Habitat overlap is another consideration; for a small fish to consume krill, both must inhabit the same waters. Fish species living in regions where krill are abundant, such as the cold waters of the Antarctic or productive upwelling zones, are more likely to encounter and consume them.
Specific examples illustrate this variability. Fish like herring, capelin, sand lance, icefish, salmon, rockfish, and flatfish are known to eat krill, often serving as a primary food source in their respective regions. Conversely, many small reef fish or gobies typically do not consume krill, as their diets are often specialized for tinier zooplankton, algae, or detritus found in their specific habitats. The presence of krill in commercial fish feed also indicates fish find them palatable and beneficial for growth.