Research shows survival of the brightest works to lure plankton and fish
If you are marine bacteria, getting swallowed and ending up in the guts of a fish is like reaching paradise.
New research has shown that bioluminescent bacteria in the deepest, darkest waters actually thrive by being eaten as they pass their way unharmed through the food chain. The findings show that the brighter they are, the great their chances of survival.
Investigating the benefits of glowing underwater, researchers at the Hebrew University of Jerusalem say they have unraveled the mystery of why the marine bacteria biologically produce light: It’s because it attracts predators.
Zooplankton, like shrimp, ingest the glowing bacteria but are unable to digest them. Instead, the bacteria continue to glow inside the zooplankton’s guts, which reveal them to their predators, fish, which can spot them easily in the dark. Further investigation of nocturnal fish that had fed on zooplankton showed that the luminous bacteria also survived the passage through the fish guts.
Why do bacteria want to be eaten? Because they get inside the guts and for them it is like the Garden of Eden. They have lots of organic material around them. They are protected and the main benefit is that they get an express train to the ocean,” Professor Amatzia Genin, the head of Hebrew University ‘s Department of Evolution, Systematics and Ecology, told The Media Line.
The findings were based on research carried out at the Interuniversity Institute for Marine Sciences in Eilat by Genin’s graduate student Margarita Zarubin from Germany in collaboration with Professor Shimshon Belkin and his student Michael Ionescu of the Hebrew University’s Silberman Institute of Life Sciences.
In an article published recently in the Proceedings of the National Academy of Sciences of the USA (PNAS), the researchers showed that nocturnal fish were easily able to detect the glowing zooplankton and eat them. On the other hand, the fish were not attracted to zooplankton that had swallowed bacteria that had undergone genetic mutation and thus did not glow.
Genin said that while bacteria glow in order to be eaten, zooplankton appeared to contradict their own survival instincts by consuming the luminous matter which exposes them and makes it easy for predator fish to find them. He explained that zooplankton seek out light in the water since that indicates the presence of a rich presence of organic material on which the bacteria grow.
The study found that bacteria only glow when they reach a quorum that showed organic material around them was very rich. This phenomenon occurs in the depths of the ocean and Genin witnessed this himself when he descended to a depth of over 3,000 meters (nearly two miles) in the Alvin submarine.
“It’s like flying in space. You have patches of light in enormous darkness. In the submarine you go through them,” he said. “The light is like truth in advertising. The glow is saying that there is a large amount of organic material. The light indicates there is lots of food. And the bacteria are happy to be eaten because they can hitchhike on the zooplankton,” said Genin.
“In the dark, deep ocean the quantity of food is very limited, therefore it is worthwhile for the zooplankton to take the risk of becoming glowing themselves when contacting and consuming the particle with glowing bacteria, since the profit of finding rare food there is greater than the danger of exposing themselves to the relatively rare presence of predatory fish,” said Genin.