Worst
Ocean Mortality Event Ever Seen: Pathogen + Human-Caused Warming
Likely Culprit in Mass Starfish Die-off
20
June, 2014
“A warmer world would be a sicker world. Under warming conditions a lot of microorganisms do better. They grow faster. They replicate faster. Many of our hosts can actually be stressed by warm conditions. And so it kind of creates a perfect storm of sickness.” — Drew Havell, Marine Epidemiologist in a recent interview with PBS.
* * * *
It
first started in the tidal basins of Southern California during
floods of warm water accompanying the El Nino of 1982-83. Laying
dormant for more than two decades, it again surfaced during the super
El Nino of 1997-98. A chronic wasting illness that obliterated whole
sea star populations along the southwestern Pacific Coast,
threatening numerous species. After each event, however, the starfish
came back. But, today, recovery is not so certain.
By
2013 human-caused ocean warming had greatly advanced. With it came a
flood of much hotter than usual water that crept up the US West Coast
beneath the influence of a devilishly persistent blocking high
pressure system. During the same year, wasting sickness again cropped
up, this time first appearing in the far northerly region off the
coasts of Washington. From there, it spread both south and north,
wiping out millions of starfish along hundreds of miles of coastline
from Alaska to California.
As
of June of 2014, almost all the starfish along the California coast
have been wiped out. Oregon and Washington’s impacts have also been
severe with entire regions showing complete or near complete losses
among the more than 20 species of affected starfish. Even typically
cold water regions have been impacted with the San Juan Islands off
Washington showing sea star losses on the order of 40% over recent
weeks and with outbreaks of the pathogen cropping up as far north as
the Alaskan coast.
The
protective cold water pools in even these zones have been greatly
eroded due to human-caused warming and this loss is what researchers
believe has allowed the pathogen to become so virulent.
A
Warming Ocean is a Deadly Ocean
The
Earth’s deep past contains a vast record of extinctions locked in
rocks deposited over millions of years. And plainly visible in this
vast history are numerous episodes during which ocean warming
resulted in mass extinctions of ocean species and, in the worst
events, land species as well. While loss of oxygen in warming oceans,
acidification, and production of deadly hydrogen sulfide gas are
thought to be among the worst of the worst monsters waiting to emerge
from hothouse seas. It is also well known that viral and bacterial
pathogens thrive in warmer environments.
Many
of these microbes arose during the warmer periods of the Earth’s
deep past. So they do not so well abide the cold. Lower temperatures
tend to reduce a pathogen’s ability to reproduce or often kills the
microbe outright. On the other hand, raising ocean temperatures is
like opening the floodgates to microbial life. And some of this life
is bound to be lethal to current organisms.
It
is thought that this is just what happened to the sea stars. The
pathogen that attacked their bodies, causing their limbs to slump or
crawl off on their own and eventually liquify in a process that seems
to more fit a sci-fi horror movie from the 1950s than current
reality, is believed to thrive in warmer seas. It lurked in the
warmest corners of the world’s oceans, only coming into contact
with the sea stars during the most extreme El Nino warming events.
That is until recent human-caused warming catapulted it into what
used to be the cold water zone off the US West Coast.
“Largest
Mortality Event We’ve Seen”
Tragically,
this recently unfettered pathogen is brutally efficient, threatening
an entire family of marine species — the keystone predator
starfish. Unchecked, it could well result in the worst ocean die-off
in modern reckoning, perhaps rivaling the loss of land amphibians due
to the human-caused spread of fungal pathogens.
(PBS documentary conducted this winter. Since the time of this video, the disease has continued to spread both within species and on to other species.)
At
first, in August of 2013, the wasting illness only affected a single
species. As of this winter about a dozen species were affected. With
the advent of spring and early summer warming over 20 species of
starfish, or about every starfish species in the affected region,
were falling victim to the illness. And though the US West Coast is
currently the most severely impacted, instances of starfish wasting
have appeared in other locales along the US East Coast and around the
world. So there is no guarantee that this outbreak will be contained
to even its current very broad range (for an interactive map of sea
star wasting sickness observations click here).
“It’s
the largest mortality event for marine diseases we’ve seen,” said
Drew Havell in
a recent interview with PBS.
“It affects over 20 species on our coast and it’s been causing
catastrophic mortality.”
Links:
Hat-tip
to Colorado Bob (who called this six months ago)
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