Glow of zooplankton (A. salina) after contacting and ingesting small particles broken off colonies of the bioluminescent bacterium P. leiognathi. The photograph on the left was taken in room light, and the photograph on the right was taken in darkness using long exposure (30 s)
Bacterial bioluminescence as a lure for marine zooplankton and fish
Some marine microbes glow in the dark. But why? A recent paper in PNAS suggests that far from deterring predators (one prior hypothesis), the behavior may serve to attract predators.
(F)indings show that the light emitted by the bacteria attracts
predators, generally zooplankton, which ingest the bacteria but are
unable to digest them. The bacteria, which continue to glow inside the
zooplankton's guts, reveal the presence of the now-glowing zooplankton,
which in turn, are attacked by their own predators -- fish -- who can
spot them readily 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. "As far as the bacteria are concerned, their access to the
fish digestive systems is like reaching 'paradise' -- a safe place, full
of nutrients, and also a means of transport into the wide ocean,"
explained Prof. Genin
But why do the zooplankton simply not learn to avoid the potentially deadly glowing bacteria?
"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," explained Prof. Genin.