The Great Die-off

Worst Ocean Mortality Event Ever Seen: Pathogen + Human-Caused Warming Likely Culprit in Mass Starfish Die-off

Robertscribbler,

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.

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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:

Sea Star Wasting Syndrome Map

University of Santa Cruz, Sea Star Wasting Page

Scientists Zero in On What’s Causing Sea Star Die-offs

Hat-tip to Colorado Bob (who called this six months ago)