Deep Sea Fish Eat Plants as They Sink

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Most research has shown that deep sea fish sit at the top of their food chains—hunting as predators and scavenging the carcasses of dead animals. Recent tests, however, have demonstrated that these denizens of the deep preserve a more generalist diet and even eat plant matter as it sinks from the surface.

The discovery, researchers say, has serious implications for our understanding of marine food webs and the carbon cycle.Dr. Rachel Jeffreys, a scientist at the Royal Netherlands Institute for Sea Research, led her team into the Atlantic Ocean off the coast of Portugal. There, they dropped spinach bait into the deep water and followed it with a video camera. Then the bait reached a depth of 3,000 meters, researchers found, it was approached by three different species of deep-water fish.

The test demonstrated for the first time that deep sea fish could sense and respond to falling plant matter. Jeffreys explained:

This highlights the variability in their diets and that they are opportunistic generalist feeder.

Though occasional plant material, researchers pointed out, enters the deep sea after being blown from land onto the ocean's surface, the majority is created by phytoplankton. Jeffreys and her team believe it is likely deep sea fish consume phytoplankton as it sinks towards the bottom of the ocean after a bloom.

She posed the question:

Because these fish are eating spinach could they then possibly feed on phytodetritus and so be affected by changes in phytoplankton communities as a result of climate change?

If this is the case, the team explained, these fish would play an important role as carbon sinks in the global cycle.