There is a new threat to sea stars called ‘sea star wasting
syndrome’, which is responsible for mass killings of these important keystone
species. In November 2013, the disease killed up to 95 percent of the sea star populations from Alaska to Orange County. Little
is known about the origins of the syndrome, or even what causes it. Scientists are trying to determine the cause
of this lethal disease before time runs out.
Typically,
a sea
star infected with the syndrome will have lesions that appear in the
ectoderm followed by decay of tissue surrounding the lesions, which leads to
eventual fragmentation of the body and death (see picture above). A deflated
appearance can precede other morphological signs of the disease. “True”
wasting disease will be
present in individuals that are found in suitable habitat, often in the
midst of other individuals that are affected. The progression of wasting
disease can be rapid, leading to death within a few
days, and its effects can be devastating on sea star populations.
“They
essentially melt in front of you,” said
Pete Raimondi, chairman of the Department of Ecology and Evolutionary
Biology at UC Santa Cruz's Long Marine Lab. The University
of California Santa Cruz is currently mapping all events along the West
Coast, and people are encouraged to report
these sea star wasting events to them.
They classify the syndrome into four categories, with 1 being mild, and
4 being severe. Pictures and
descriptions for the severity of the syndrome can be found here.
At
first, the disease only infected one species, Pycnopodia helianthoides, also known as the sunflower star. Then the disease began to affect a more common
sea star species, Pisaster ochraceus
(Robert Paine’s keystone species). Now,
there are about 12-15
species that are dying along the West Coast from sea star wasting syndrome. And wild sea stars are not the only ones in danger--
in September
2013, sea stars in an aquarium at the Gulf of the Farallones National
Marine Sanctuary visitor center at the San Francisco Presidio contracted the
syndrome in water pumped from the ocean.
Eels, sculpin and anemones that were in the same aquarium were unaffected.
The probable
cause of the disease on the west coast of the US is caused by a pathological
agent, such as bacterium (vibrio), although a recent wasting event on the east
coast of the US has been attributed to a virus. Sea star wasting events have also occurred
from British Columbia down to the Gulf of California, the Mediterranean and the
North Atlantic coast of North America, but not in the Southern Hemisphere. Some researchers have suggested that Fukushima
could be a cause, but the sea stars are being affected on the east coast, so
this is not likely. The ultimate
cause is not clear although such events are often associated with warmer
than typical water temperatures as was the case for the major die off in
southern California in 1983-84 and again in 1997-98. Sea stars are susceptible to bacterial
infection, and warmer water boosts bacteria growth, Raimondi
said.
If the cause for sea star wasting syndrome is not uncovered,
ecosystem balance can be disrupted with the disappearance of sea stars. As we have learned in class, removing Pisaster ochraceus from tide pools
causes unchecked population growth of mussels and other organisms. Also, with global climate change,
temperatures will rise in the ocean, which could have significant
or even profound effects on populations. Hopefully the cause of sea star wasting
syndrome can be solved before it is too late.
