Climate crisis: Warming oceans linked to mass starfish die-offs around the world

Wasting disease leaves creatures ‘drowning’ in their own environments, scientists say

Harry Cockburn
Thursday 07 January 2021 13:00
Starfish on the west coast of America dying due to the wasting disease
Starfish on the west coast of America dying due to the wasting disease

A massive die-off of starfish across the world, leading some species to the brink of extinction, has been linked to warming ocean temperatures caused by the climate crisis, scientists have said.

For more than seven years, a mysterious wasting disease, which turns starfish (also known as sea stars) into “piles of goo”, has caused mass mortality events capable of upending food chains in affected areas, which have been recorded from Alaska down to the gulf of Mexico.

Researchers have previously described it as the single largest, most geographically widespread marine disease ever recorded.

But new research suggests the starfish may be dying due to respiratory distress and literally “drowning” in their own environments due to higher levels of microbial activity caused by local organic matter thriving in warming oceans.

The research team, led by marine biologists at Cornell University, said the changes to the environment “rob the creatures of their ability to breathe”.

“As humans, we breathe, we ventilate, we bring air into our lungs and we exhale,” said Ian Hewson, professor of microbiology at Cornell University.

“Sea stars diffuse oxygen over their outer surface through little structures called papulae, or skin gills. If there is not enough oxygen surrounding the papulae, the starfish can't breathe.”

According to Professor Hewson, ocean conditions lead to the production of unusual amounts of organic material, which he said prompts bacteria to thrive.

As bacteria consume the organic matter, they deplete the oxygen in the water - creating a localised low-oxygen environment which can surround starfish and lead to deflation, discoloration, puffiness, and limb twisting or curling.

“It's a cascade of problems that starts with changes in the environment, Professor Hewson said.

Most of the organic matter comes from the release of discharge from microscopic algae, zooplankton excretion, and from decaying animal carcasses.

Together these stimulate a group of bacteria called copiotrophs, which survive on carbon and rapidly consume organic matter.

The copiotrophs also need to breathe, so while absorbing the organic matter, they simultaneously deplete oxygen in starfishes’ watery habitats.

“It's organic matter concentrations in the water,” he said.

“If you have a dead and rotting starfish next to starfish that are healthy, all of that dead one's organic matter drifts and fuels the bacteria, creating a hypoxic environment. It looks like disease is being transmitted.”

Professor Hewson said that though more scientific work must be done, the research “reframes the discussion about marine disease ecology, which has focused on pathogenic disease”.

“We should now include microorganisms that don't directly cause the pathology, since they may hold a key to affecting sea star health.”

The research is published in the journal Frontiers in Microbiology.

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