November 25, 2013 at 3:19 am #1296MikeKeymaster
This is an older article, but very interesting.
Scientists Discover Mystery Krill Killer
for National Geographic News
July 17, 2003
Scientists have discovered a tiny, one-celled parasite that causes a
grisly and fatal infection in krill. Masses of the parasite grow
inside the krill, eat its organs, divide, and then burst out of
their host’s dead body in search of new victims.
The discovery sheds more light on a key player in ocean’s food
chain. Scientists previously thought most animals like krill were
either eaten by larger predators or simply starved to death. The
find shows that parasites also play an important role.
The scientists, led by marine biologist Jaime Gómez-Gutiérrez, a
researcher at Mexico’s Centro Interdisciplinario de Ciencias Marinas
in La Paz and currently a Ph.D. graduate student at Oregon State
University in Corvallis, found infected krill—called euphausiids—at
more than a dozen sites along the Oregon and Washington coasts.
At a site off the coast of Astoria, Oregon, researchers found a
massive die-off in a krill swarm, with carcasses littering a 0.9-
mile (1.5-kilometer) stretch of the sea floor.
“Because they cause mass mortality, they literally compete with
other predators of euphausiids,” said Gómez-Gutiérrez. “If the mass
mortality occurs frequently, they can have a significant impact on
euphausiid and predator production.”
Keith Reid, a krill expert with the British Antarctic Survey in
Cambridge, England, said the research highlights “a potentially
important cause of mortality that should be considered along with
traditional contributors to mortality.”
Prior to this research, which is published in the July 18 issue of
the journal Science, mass mortality of krill caused by a parasite
had not been recorded.
The exploding krill were first discovered during a research cruise
off Newport, Oregon, in July 2000 by William Peterson, a fisheries
oceanographer at the National Oceanic and Atmospheric
Administration’s Hatfield Marine Science Center in Newport.
Gómez-Gutiérrez, Peterson’s graduate student, and colleagues carried
out detailed studies of the phenomenon. On several research cruises
in 2002 they found infected krill at seven percent of the 313 sites
The parasite infects three out of the 14 species of krill that live
in this region: Euphausia pacifica, Thysanoessa spinifera, and
Thysanoessa gregaria. The infected creatures were mostly found along
continental shelf breaks—areas where the ocean floor steeply drops
and where krill are most abundant.
“Most of the euphausiids have a very big concentration there, and
the parasites prefer those locations for infection,” said Gómez-
In 2001, Hatfield Marine Science Center oceanographers Alex de
Robertis and Richard Brodeur used a remote-controlled robot to study
and collect krill from a continental shelf break off the coast of
Astoria. They found a mass mortality of E. pacifica on the sea floor
at depths ranging from 722 to 1,804 feet (220 to 550 meters).
“We found the parasite on several cruises but never thought they
could cause mass mortality,” said Gómez-Gutiérrez. “Alex and Rick
recorded it with the robot’s video camera and even collected a few
The collected carcasses from the mass mortality exhibited the same
infection signs as infected krill the researchers had studied in
their ship-based laboratory. Like the other infected krill, the
parasite eluded precise identification.
The researchers determined the krill killer was of the genus
Collinia but different than the parasite Collinia beringensis, which
has been found to infect the krill Thysanoessa inermis in the Bering
Sea. Gómez-Gutiérrez and colleagues are in the process of naming the
Reid noted that infection of this type has not been seen anywhere
else. “Such parasitism has not been recorded in all species of
krill. It has not been seen in Antarctic krill [Euphausia superba]
or in the Northern krill [Meganyctiphanes norvegica] in the North
Gómez-Gutiérrez said that he does not know how the parasites get
inside the krill, but that once inside they eat all the krill’s
organs. The krill, which are usually transparent with small red
spots, turn orange and their shells swell.
The parasites then multiply rapidly, forming cells that are ready
for transmission to a new host. These transmission cells burst out
of the krill body, leaving a ruptured carcass on the ocean floor.
The researchers say that infected krill die within 24 to 72 hours.
Once the parasite has killed the host and spread transmission cells
into the water it has approximately two to three days to find a new
victim in order to continue its lifecycle.
Gómez-Gutiérrez and colleagues suggest the parasite is most
successful in krill swarms, given its need to find a new host
quickly. Krill form swarms to improve their ability to capture prey,
find mates, and avoid predators such as whales, salmon, and other
fish. However, the dense swarms also make it easier for parasites to
spread, the researchers say.
Reid agrees that the swarming nature of krill likely increases their
susceptibility to the parasites. “However, there are a suite of
positive aspects of forming swarms that one would presume outweigh
the potential negative consequences of doing so. If this were not
the case, we would not find krill living in swarms,” he said.
In future studies, Gómez-Gutiérrez and colleagues hope to discern
how this parasite impacts the food chain.
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