Scientists: Climate Change Is Killing Life at the Bottom of the Sea

Number of fish and species diversity was shockingly sparse 7 kilometers down, team concludes.

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Climate change isn't a matter of controversy– the planet's climate changes all the time and is arguably doing so now. The question is what's causing it, which is arguable. Less controversial is what climate change is causing, and now scientists suspect the effect at the bottom of the sea is much worse than had been thought.

Scientists from the University of Aberdeen and New Zealand sent cameras to a depth of 7,000 meters - 4.5 miles - to record rarely-seen creatures on the floor of the New Hebrides Trench in the South Pacific.

The researchers had expected to see more variety in the previously unexplored trench, they say. They believe climate change could be having an impact even in the deepest reaches of the ocean.

The New Hebrides Trench lies between New Caledonia and Vanuata, to the West of the Coral Sea in the South Pacific. It's 750 miles long and 45 miles wide, plunging to a depth of 7,600 meters in places.

During a voyage to the region in November and December last year, the scientists captured hours of footage of rarely-seen animals – but were shocked to see a much sparser and less diverse range of life than expected.

Large red prawns and Cusk eels were abundant, with arrow-tooth eels and smaller crustaceans also present but despite a total of 27 different camera deployments - little else was spotted.

The researchers suggest that changing water temperatures higher up in the ocean are "trickling down" to the ocean floor.

"We set out to investigate whether the patterns of biodiversity in these medium depth trenches could be predicted by trends that we have observed in the really deep trenches that we've already studied elsewhere in the Pacific Rim," said voyage leader Dr Alan Jamieson, of the University of Aberdeen's Oceanlab. "But what we found was an entirely different deepwater fish community.

"Fish were surprisingly few in number and low in diversity and not at all what we expected. The fish we would always expect to see, the grenadiers, were completely absent. The fish that dominated the area were a group called cusk eels which are far less conspicuous elsewhere."

The scientists say the New Hebrides Trench lies underneath tropical waters, which are typically less productive than the waters around the Pacific Rim.

"The waters over a trench are what 'feeds' the deep sea community and in this case it appears that the prawns and cusk eels are specialists in low food environments. This means the huge expanses of the deep Pacific Ocean that span the tropical regions are likely to be largely inhabited by the cusk eels and prawns rather than the more diverse communities we see around the Pacific Rim. If that is the case it also means that these animals are far more widespread than previously thought," said Thom Linley, fellow marine biologist from Oceanlab.

The team says that any change in temperature at higher levels is likely to have a cascading effect on the deep sea community. The deep sea is potentially a kind of silent victim in the era of a changing climate, they concluded.

A Spectrunculus grandis, better known as a cusk eel, filmed at a depth of more than 3 km.Credit: SIMoN, Wikimedia Commons

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