Bioluminescence, Part 2

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

Looking for fish beneath cliffs of Laird's Sandstone on Tomales Bay
Photo by Casey Newman, 2011, All Rights Reserved.

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.

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.

To hear the plainfin midshipman fish’s hum, visit Discovery of Sound in the Sea: http://www.dosits.org/audio/fishes/plainfinmidshipman/.