North Pacific Krill, Euphausia pacifica
North Pacific Krill, Euphausia pacifica.Krill collected off the surface with a bait net near the Gordo I Bank, Baja California Sur, May 2001.
Phylogeny: The North Pacific Krill, Euphausia pacifica (Hansen, 1911), is a member of the Euphausiidae Family of Krill. The genus Euphausia is one of ten genera in this family, and there are thirty-one species in this genus. They are also known as Isada Krill and in Mexico as eufausiáceo and kril pacífico. There are two families that make up the Krill Order- Benteuphausiidae and Euphausiidae; these only families differ in that Euphausiidae Krill are bioluminescent. The name krill is Norwegian, meaning whale food.
Morphology: North Pacific Krill are small, shrimp-like animals in the Phylum Arthropoda, meaning that they have jointed legs. They are crustaceans, with the carapace fused to the thoracic segments, and their eyes on stalks. Their pleopods (abdominal segments) function as swimmerets. North Pacific Krill have large, round eyes. They lack a rostrum and abdominal spines. There is one pair of lateral denticles on the carapace. They are translucent whitish in color. They reach a maximum of 2.5 cm (1.0 inches) in length.
Habitat and Distribution: North Pacific Krill are a pelagic species. They are abundant in the temperate and polar regions of the Pacific Ocean, often comprising the greatest biomass in these areas. They can form dense (up to 10,000/ cubic meter) shoals that can stretch for miles. North Pacific Krill are strong vertical migrators, spending the day 400-1,000 meters deep and ascending to surface waters during the night. This behavior helps them avoid shallow water predators and still feed in the nutrient rich surface waters. In Mexican waters they are limited to the west coast of the Baja Peninsula, ranging south to, at least, Magdalena Bay. Water Temperatures, currents, and El Niño/La Niña patterns strongly impact their north/south range. North Pacific Krill are one of fifteen species of krill found along Mexico’s west coast.
Diet: North Pacific Krill are omnivores that feed on planktonic algae, diatoms, and zooplankton. They feed on phytoplankton by filter-feeding, but can also raptorially feed on larger particles.
Predators: North Pacific Krill are vitally important food for birds, fish, seals, squid, and baleen whales. They play a key role in transferring energy from lower to higher trophic levels.
Reproduction: North Pacific Krill are gonochoric (male or female for life). They reproduce sexually, with males producing spermatophores and transferring them to the female’s abdomen. The female stores the male’s sperm and releases it to fertilize her eggs. The fertilized eggs hatch as non-feeding nauplii, living off the yolk. They pass through several larval stages, over about four months time, before reaching their adult phase. Females can produce many sets of eggs (totaling more than 20,000) during the summer spawning season. Males take part in one breeding season and live about two years. Females live longer and take part in two breeding seasons.
Ecosystem Interactions: The parasite Thalassomyces fagei, of the Ellobiopsidae family is known to affect the maturation, molting, and growth of North Pacific Krill. The apostome ciliate, Collinia oregonensis and other epibionts also inhabit this species.
Human Interactions: North Pacific Krill are harvested mainly as a food supplement for both fish farms (giving salmon their ‘pink’ color) and aquariums. In the western Pacific they are also used for human consumption in limited quantities. They are critically important in supporting many other fisheries. From a conservation perspective they have not been formally evaluated however they are common with a wide distribution and should be consider to be of Least Concern.
Synonyms: None
Predators Their predators are mainly finfish and baleen whales (picture of krill: stomach content of Bryde whale). Krill are a large dietary proportion of many local finfish (hake, herring, rockfish, salmon) and if krill stocks should fall, finfish could be affected. Humans are also a predator. A emerging commercial krill fishery exists on the B.C. coast with a current annual limit of 500 tonnes. Fresh, uncooked euphausiids have almost no taste. Frozen or dried krill develop a strong, rather discouraging flavor. They constitute the ocean’s richest source of protein and are rich in vitamins (especially vitamin A)
Biotic association Some organisms are associated with the Euphausia pacifica but it seems that few are identified. Some of the identified ones are cilliates attached to eggs of the krill, and tthat belongs to the family (Protista (Incertae sedis)) and infests the euphausiids. The Ellopbiopsidae have been classified at various times as protistans, colorless algae, fungi, or protozoans. They are multinucleate protistans with reproductive structures outside the host (here Euphausia pacifica) and absorptive portions inside. The organ of fixation has fine protoplasmic filaments, which are believed to absorb nutrients from the host. The parasite usually the Euphausia pacifica.