Museum biological collections are the records of life on Earth and as
such, they are frequently used to investigate serious environmental
issues. When public health officials were concerned about the levels of
mercury in fish and birds, for example, scientists studied museum
specimens to assess historical changes in mercury contamination. Eggs in
museum collections were analyzed to establish the connection between
DDT, thinning eggshells, and the decline in bird populations. And now,
specimens from the Natural History Museum of Los Angeles County (NHM)
have helped explain the mysteriously sudden appearance of a disease that
has decimated sea stars on the North American Pacific Coast. In a paper
published Monday, November 17, 2014 in the journal Proceedings of the National Academy of Sciences,
Cornell University microbiologist Ian Hewson and colleagues identify
the Sea Star Associated Densovirus (SSaDV) virus as the microbe
responsible for Sea Star Wasting Disease (SSWD). NHM Curator of
Echinoderms Gordon Hendler and Collections Manager Cathy Groves, along
with scientists from universities and aquariums along the coast
(including NHM neighbor, the California Science Center), collaborated in
the study.
Since June 2013, the largest die-off of sea stars ever recorded has
swept the Pacific Coast. At least 20 different species of sea stars have
been affected -- including iconic species like the "ochre star" and the
multi-armed "sunflower star" -- and many populations of sea stars from
Southern Alaska to Baja California have already disappeared.
Their large-scale disappearance is anticipated to have a serious and
long-lasting ecological impact on coastal habitats, because sea stars
are voracious predators, with a key role in regulating the ecology of
the ocean floor.
Museum samples prove that the virus has existed at a low level for at
least the past 72 years -- it was detected in preserved sea stars
collected in 1942, 1980, 1987, and 1991. The study suggests the disease
may have recently risen to epidemic levels because of sea star
overpopulation, environmental changes, or mutation of the virus.
The study detected the virus on particles suspended in seawater, as
well as in sediment, and showed that it is harbored in animals related
to sea stars, such as sea urchins and brittle stars. Likely it can be
transported by ocean currents, accounting for its rapid, widespread
dispersal in the wild. Since the die-off began, the disease has caused a
mass mortality of captive sea stars in aquariums on the Pacific Coast,
although it did not spread in aquariums that sterilize inflowing
seawater with UV light.
"There are 10 million viruses in a drop of seawater, so discovering
the virus associated with a marine disease can be like looking for a
needle in a haystack," Hewson said. In fact, the densovirus is the first
and only virus identified in sea stars. However, its discovery will
enable scientists to study how the virus infects sea stars and trace it
in the ocean. Further research could reveal how the virus invades its
host, why kills some sea stars, and why other species are unaffected.
Research might also identify factors that triggered the ongoing
plague and help to predict or forestall similar events in the future.
"A recent publication highlighted examples of innovative studies for
which museum time-series were integral in identifying responses to
environmental change and bemoaned general decline in the growth of
museum collections," said NHM's Hendler. "Fortunately, we bucked the
trend and intentionally collected common, local species of sea stars,
which made it possible to detect SSaDV in specimens from NHM!"
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