Head to head
Copepod vs Krill
A copepod and krill are both small, extremely abundant marine crustaceans that anchor ocean food webs from the bottom up, and they are often mentioned in the same breath as competitors for the title of most important, and most numerous, animal group in the sea.
| Copepod | Krill | |
|---|---|---|
| Typical adult size | About 1 to 2 mm | About 1 to 6 cm |
| Body shape | Teardrop-shaped | Shrimp-like |
| Eyes | Often a single simple eye | Paired compound eyes |
| Total abundance | Possibly the most numerous animal group | Extremely abundant, especially in polar seas |
| Famous predator link | Larval fish, small fish | Baleen whales |
| Daily vertical migration | Yes | Yes |
| Diet | Phytoplankton, bacteria | Phytoplankton, zooplankton |
| Conservation status | Least Concern | Least Concern |
Copepod vs Krill: common questions
Which is more numerous, copepods or krill?
Copepods are generally considered far more numerous than krill in total individual count, with some scientists describing copepods as the single most abundant animal group on the planet, though krill can still form absolutely enormous, dense swarms, particularly in polar waters, and represent a very large total biomass in their own right. The key difference is scale of individual size versus sheer numbers, with copepods winning decisively on raw count while krill, being considerably larger per individual, still contribute an enormous total mass of living material to the ocean.
Why are krill more famous than copepods despite copepods being more numerous?
Krill are considerably larger and more visible than copepods, forming dense, easily observed swarms that can be seen from boats or even from the air, and their status as the primary food source for several iconic baleen whale species, including blue whales, has given them significant public attention and cultural recognition. Copepods, despite their crucial ecological role and probably greater total abundance, are microscopic and far less visually striking, which has left them comparatively obscure outside of scientific and fisheries research circles.
Do copepods and krill compete with each other for food?
To some extent, yes, since both feed heavily on phytoplankton and, in the case of krill, sometimes on smaller zooplankton including copepods themselves, meaning there can be a degree of dietary overlap and even direct predation between the two groups in areas where both are abundant. In practice, however, the ocean's overall phytoplankton and zooplankton production is generally large enough, and the two groups often occupy sufficiently different size niches and regions, that both can remain extraordinarily abundant simultaneously rather than one group's success coming primarily at the direct expense of the other.