Hawaiian Bobtail Squid

Hawaiian Bobtail Squid (Euprymna scolopes)

Hawaiian Name: Mūhe‘e (Squid)

Family: Sepiolidae

Endemic

If you were swimming in the deep, dark ocean, wouldn’t it be nice to have a flashlight?  The Hawaiian bobtail squid has one!  The flashlight is built right into the squid’s body, and is known as the light organ.

[Illustration: Squid shining light at ocean floor]

 

Ka hana a ke aloha, he kohu mūhe‘e i ke alo pali.

The action of a lover is like that of a squid at the face of a precipice.

A squid is said to be a creature that goes every which way. A squid-like

lover is not to be trusted.

                                                            (Pukui: 1296-141)

 

The Hawaiian squid, usually about 2 inches (5 cm) long, is a cephalopod that lives in the shallow waters around the Hawaiian Islands.  The squid is mostly brown, with some iridescent green and blue spots, and has eight arms as well as two longer tentacles. 

Bioluminescent bacteria (Vibrio fischeri), which produce light, live in a specialized body cavity in some Hawaiian squids of the genus Euprymna, including the Hawaiian bobtail squid. 

 

Bioluminescence

Bioluminescence occurs in and around the ocean in a variety of ways.  In the Hawaiian bobtail squid, bioluminescent bacteria function like a flashlight built into the squid’s body.  The specialized cavity in the squid’s body where the bioluminescent bacteria live is known as the light organ, and it is located on the squid’s underside.

The squid and the bacteria both benefit from their partnership, and so it is a symbiotic relationship.  The bioluminescent bacteria get a good place to live from the squid as well as essential amino acids and other nutrients, while the squid uses the bacteria’s light to provide camouflage that helps it move and hunt at night without being detected by predators. 

During the day the squid buries itself in the sand in shallow coastal waters.  Then at night the squid comes out to hunt for food.  The squid points its light organ downward as it hunts, emitting light toward the seafloor to conceal any shadow that might be caused by the starlight or moonlight coming down from the surface.  

The squid senses how much light is needed, and then dims or brightens the light produced by the bioluminescent bacteria by controlling the amount of oxygen that goes into its light organ. 

The glow-in-the-dark bacteria manufacture luciferase, an enzyme that facilitates a biochemical reaction that produces light.  The bacteria only glow when a critical concentration of luciferase is reached, and this is dependent upon the amount of oxygen available.

Every morning the squid expels more than 90% of all the bacteria in its light organ back into the ocean, and then new bacteria move in.  The bacteria multiply during the day and then begin glowing again by nightfall, when the next hunt begins.

  Researchers are studying this enzyme process as a rare model of the cell-to-cell communication that allows some bacteria species to coordinate their activities.  These bacteria also provide scientists with a useful model of the animal-bacteria symbiotic relationships that also occur in humans.

[Photograph: Squid]