They are slimy, some of them are transparent and kind of creepy and you wouldn’t want to encounter one on an ocean swim, but luckily you never will.
- A CSIRO voyage to the Southern Ocean has examined the creatures that live in the ocean’s ‘twilight zone’
- Scientists hope their findings will help them better understand the ocean’s ability to store carbon
- The researchers are also looking at how climate change is impacting its carbon storage
These are the creatures of the Southern Ocean’s “twilight zone” — a 200- to 1,000-metre layer of water that lies just beyond the reach of light.
The researchers who collected them have just returned from a six-week trip on the CSIRO’s Investigator research ship.
But the trip was about a lot more than collecting the weird and wacky marine life.
“The voyage focused on creatures that are called micronekton, for example small fish and squid, crustaceans, and jellyfish,” said marine biologist Svenja Halfter.
“Micronekton undertake large vertical migrations through the water column: they swim up to the surface at night to feed and migrate further down during the day to avoid being seen by predators.
The voyage, known as the Southern Ocean Large Area Carbon Export (SOLACE), features contributions from CSIRO, the University of Tasmania’s Institute for Marine and Antarctic Studies, Australian National University, Curtin University and the Australian Antarctic Program Partnership (AAPP).
The 20 researchers on board have completed what they say is the most extensive study of the Southern Ocean of its kind, and they are hoping it will help them understand how the ocean stores carbon.
“The ocean plays a role in the global carbon cycle that is every bit as important as the forests on land,” said voyage chief scientist Phillip Boyd.
He said the “driving force” were the billions of tiny plankton that capture carbon from the atmosphere through photosynthesis, much like plants.
When these organisms die or are consumed by the creatures that migrate to the upper levels of the ocean, the waste forms something known as a marine snowfall.
“It looks like a snow shake [globe]. You have this material sinking down [to the sea floor] and that’s taking carbon out of circulation for centuries or longer,” he said.
So where do the creepy critters come in?
“We call this the active carbon pump because it injects carbon into the deep sea, where bacterial recycling rates are slower than at the surface,” said Ms Halfter.
Marine biologist Caroline Sutton said they want to know “who’s there, where they are, how they’re moving and who is eating who”.
“We can take a tissue sample and work out where they’re eating,” she said.
“If they’re eating zooplankton and then moving down then they’re taking that [carbon] with them.
She said scientists will also try and work out how much carbon the creatures store.
“What we’ll do is get the samples, dry them up and burn them up and work out how much energy they’ll give off and that’s how much carbon they’ve got stored in them,” she said.
Ms Sutton said the most abundant animals in their samples were the gelatinous ones.
The question the scientists are also asking is how climate change could affect the ocean’s ability to store carbon.
“As the ocean warms, it actually changes how productive it is, it changes the amount of marine snow going into the deep ocean so it may actually alter some of those processes significantly,” Professor Boyd said.
“It’s more difficult for the plant nutrients that are plentiful in the deep ocean to come to the surface so it may slow up the growth of the plankton and slow down the amount of snow sinking into the deep ocean.”
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