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Thousands of jumbo squid have beached themselves on central California
shores this week, committing mass "suicide." But despite decades of
study into the phenomenon in which the squid essentially fling
themselves onto shore, the cause of these mass beachings have been a
mystery.
But a few intriguing clues suggest poisonous algae that form so-called red tides may be intoxicating the Humboldt squid
and causing the disoriented animals to swim ashore in Monterey Bay,
said William Gilly, a marine biologist at Stanford University's Hopkins
Marine Station in Pacific Grove, Calif.
Each of the strandings has corresponded to a red tide, in which algae
bloom and release an extremely potent brain toxin, Gilly said. This
fall, the red tides have occurred every three weeks, around the same
time as the squid beachings, he said. (The squid have been stranding in
large numbers for years, with no known cause.)
"It's not exactly a smoking gun, but it's pretty circumstantial evidence that there is some link," Gilly told LiveScience.
For decades, beach lovers have reported bizarre mass strandings where throngs of Humboldt squid (Dosidicus gigas), also called jumbo squid, fling themselves ashore, said Hannah Rosen, a marine biology doctoral candidate at the Hopkins Marine Station.
"For some reason they just start swimming for the beach," Rosen told
LiveScience. "They'll asphyxiate because they're out of the water too
long. People have tried to throw them back in the water, and a lot of
times the squid will just head right back for the beach."
Before this, scientists in 2002 and 2006 noticed mass squid strandings
from the Gulf of Mexico all the way to Alaska, Gilly said.
But the cause of the mass squid
deaths was an enigma. The strandings seem to happen whenever schools of
squid invade new territory, leading some to suggest the creatures
simply get lost and don't realize they are out of the water until it is
too late. The squid washing ashore are juvenile size, about 1 foot (0.3
meters) long, and hadn't been traveled to Monterey Bay before this fall.
This season's stranding, which started Oct. 9, happened around the time
Humboldt squid entered the bay.
Other scientists have proposed that red tides that release a lethal
toxin called domoic acid may be intoxicating the squid and disorienting
them. But when researchers tested the stranded squid for domoic acid,
they found only trace amounts of the chemical, Gilly said.
The poisonous chemical mimics a brain chemical called glutamate in
mammals, though domoic acid is 10,000 times more potent than glutamate.
The similar structure means domoic acid can bind to glutamate receptors
on neurons. In turn, the receptor opens channels that let calcium into
the cell. At high levels the poison causes brain cells to go haywire and
fire like crazy, so much that they fill up with calcium, burst and die,
Gilly said. (10 Weird Facts About the Brain)
Humans who eat shellfish contaminated with this red-tide toxin get amnesic shellfish poisoning,
because the toxin destroys their brain's memory center called the
hippocampus. Sea lions that eat similarly poisoned anchovies or krill go
into seizures or become disoriented and behave bizarrely.
However, no one has tested the effects of lower levels of the chemical on squid.
But new evidence points to the red tide as at least one cause of the
mass strandings. While most sea life follows daily tidal or lunar
cycles, the mass deaths seem to be happening every three weeks. That led
one of Gilly's graduate students, R. Russell Williams, to see if
something in the environment was leading them astray.
"He was fixated in finding some kind of environmental signal," Gilly said.
Russell found that red tides occurred every three weeks, around the
same time as the squid strandings, suggesting a link, Gilly said.
While past researchers have only found trace levels of the toxic
red-tide chemical in stranded squid, low doses of domoic could
essentially be making the squid drunk. Combined with navigating
unfamiliar waters, that could cause the mass die-offs.
"They could be tipped over the edge by something like domoic acid that might cloud their judgment," Gilly said.
This isn't the first time Gilly and his colleagues have been led on a
CSI-like hunt for Humboldt squid. In 2011, they figured out why the
elusive jumbo squid left their usual feeding grounds off the Baja
California coast in the winter of 2009 to 2010. Apparently, the squid
had moved north, following their prey, small, bioluminescent fish called lantern fish, which had also moved north due to El Niño weather patterns.
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