Krill deaths a mystery – 09/23/2006

  • November 25, 2013 at 3:19 am #1296

    This is an older article, but very interesting.
    Scientists Discover Mystery Krill Killer
    John Roach
    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.

    New Parasite?

    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
    they sampled.

    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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