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By Mary Jane Schramm
National Marine Sanctuary Program

Its size is tiny, but its significance is colossal.   Krill – a shrimp-like crustacean – forms the basis of the marine food web for whales, seabirds, fish, squid, seals, and sharks throughout the world’s oceans. Along California’s coast, the California Current ecosystem’s unique springtime wind and circulation patterns generate upwelling of nutrient-rich, deep ocean waters to the sunlit upper layers, which results in an extraordinary explosion of biological productivity. And in this system, krill is king.

Rockfish in Channel Islands National Marine Sanctuary
Squid, rockfish and salmon thrive on krill. Click on squid image for more information and a video.
Krill is the near-exclusive food for giant blue whales, and seabirds like auklets and shearwaters. Commercially valuable salmon, rockfish, flatfish, sardines and squid thrive on krill. When abundant, animals migrate thousands of miles to feed on krill. But when absent, the entire marine ecosystem suffers. Animal migration patterns may shift causing starvation for species unable to forage elsewhere; complete breeding failure for some seabird species occurs, and local ecosystems face collapse.

Of the 85 species of krill worldwide, the dominant species in central and northern California are Thysanoessa spinifera and Euphausia pacifica, both less than an inch long. Grazing on microscopic plants called phytoplankton, krill, a type of zooplankton, transfer energy to larger creatures upward through the food web. From late spring into fall, krill may swarm in swirling bait balls as dense as 100,000 per cubic yard, migrating vertically in the water column. At times broad, pink swaths of it may stretch for miles and can be seen form the air.

In California sanctuary waters in a normal summer-fall season, a single blue whale can consume up to four tons of krill each day. And roughly 2,000 blue whales – perhaps a sixth of the global population – generally feed here. But in 2005 and 2006, all that changed.

During those years, researchers theorize, atypical weather patterns produced the wrong rhythm of wind and calm needed for upwelling. Consequently, krill were so sparse that seabird chicks, unable to eat large prey, died of starvation; nests were abandoned. Beach Watch coastal surveyors documented the dead seabirds. Blue whales that usually feed off central and northern California hunkered down in lower latitudes where at least some food was available. The outlook was grim, and scientists feared that a third, fourth or even fifth year without krill could have terrible consequences on the entire ecosystem.

In 2007, upwelling in the California Current – albeit late – has finally set in, and preliminary results indicate these important zooplankton are returning. Scientists are guardedly optimistic that krill will rebound.

“Sanctuaries cannot control natural processes that affect krill, but they can prevent human-caused stresses that compound them, such as oil pollution and other kinds of habitat destruction,” said Maria Brown, Gulf of Farallones, National Marine Sanctuary superintendent. “Cumulative stresses could trigger a domino effect, resulting in major ecosystem impacts. With effective regulations and development of a dynamic ocean stewardship ethic, sanctuaries can enhance nature’s inherent resiliency to cope with change. Sanctuaries play an ongoing, critical role in the balance of life within our world ocean.” 

Despite its importance to marine ecosystems, some krill populations are exploited by humans, primarily as livestock and farmed salmon feed. Antarctic populations are heavily harvested. But off North America’s west coast, recognizing its importance in maintaining ecosystem integrity, the Pacific Fisheries Management Council voted in March 2006 to prohibit commercial krill fishing in federal waters off California, Oregon, and Washington.

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Revised September 12, 2023 by Sanctuaries Web Team | Contact Us | Web Site Owner: National Ocean Service
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