Bioluminescence is produced by a chemical reaction similar
to the one that happens when a glow stick is broken. This reaction releases
energy as light. The color of the light that is produced is usually blue or
green, but can be red, yellow, or orange, depending on the chemicals used in
the reaction. Most animals produce only one color of light, but some fish and
worms use two colors of light
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Looking for fish beneath cliffs of Laird's Sandstone on Tomales Bay
Photo by Casey Newman, 2011, All Rights Reserved. |
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Some animals, like fish and shrimp, use photophores, or
special organs to produce light. Others, such as jellyfish, have specialized
cells scattered over their bodies that glow. Certain species of organisms play
host to bioluminescent bacteria, which produce light in exchange for room and
board. There are some species of squid that produce bioluminescent ink, which
is squirted out as a defense mechanism.
Single celled organisms such as bacteria and dinoflagellates use special
compartments in their cell to separate the chemicals that react to produce
light, combining the compartments when necessary.
At depths of between 200m and 1000m in the ocean, up to 90%
of animals use bioluminescence to blend in with their surroundings. The light
that reaches down into those depths is blue-green, and these animals will use
bioluminescent photophores (cells or organs that produce light) to match the
amount of blue-green light around them, camouflaging themselves. Other fish that live at those depths
produce red light. Many organisms that live that deeply cannot see red light,
so the fish that produce it can use the light to see their prey without being
seen. Deeper in the ocean, where
conditions are always cold and dark, animals do not need bioluminescence to
blend in, but they do use it to attract prey and for communication and courtship.
These animals have unique patters of photophores, which may help them to
recognize others of their species.
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Plainfin Midshipman Fish
Photo copyright Terrence J Fidler, 2006,robots4farms.com |
One type of bioluminescent fish, called the plainfin
midshipman fish, lives deep in the Pacific Ocean but migrates to the coast in
the summer to lay their eggs. These fish are a type of toadfish with no spots
or stripes on their dorsal fin. Their photophores are arranged in a U-shape on
the underside of their body, and the photophores look like the buttons on a
naval officer’s uniform, which is how they get the name midshipman fish. The
photophores are used to blend in with the light around them while they are in
the ocean, which keeps predators from seeing them from below.
The male midshipman fish returns to Tomales Bay first,
digging out a nest in the rocks along the shoreline. The rocks at Nick’s Cove
are a favorite spot for these nests. Once there, the males begin to hum to
attract females. The hearing of the female midshipman fish is so accurate that
they can tell the difference between each male’s hum and find the nest of the hum
they like best. Once there, the female will lay her eggs and return to the open
ocean. The males fertilize and take care of the eggs, continuing to hum until
their nests are full of eggs from many females. The males guard the nest until
the eggs hatch and the hatchlings are ready to be on their own.
