Heteroteuthis & Euprymna: Underwater Light Warriors
(beautiful Hawaiian bobtail squid)
If you know anything about squids, you probably know about their infamous ink attacks. As explained in our squid dissection video here, countless species of squids utilize an ink-spray defense mechanism, where they spray clouds of jet-black ink at incoming predators. The darkness of the discharge as well as its alkalinity blinds and deters the predators, buying time for the squid to escape. However, there are two unique species of squid that decided the ink-spray method was too cliche, and adopted a self-defense mechanism that utilizes bio-luminescence, or the power of light.
Heteroteuthis dispar, also known as the odd bobtail, is a small deep-water squid species found in the Mediterranean and the North Atlantic Ocean. The odd bobtail squids have ink sacs, which they often use to spray clouds of ink at incoming predators, but they decided to do one more. Near the ink sacs in a Heteroteuthis squid is located a small gland that produces and shoots out a bio-luminescent mucus when threatened. This jet of light that shoots out takes a while to dissipate, giving the squid ample time to escape as well as the nickname ‘fire shooter.’
Euprymna scolopes, also known as the Hawaiian bobtail squid, is a close cousin of the Heteroteuthis dispar that makes home in the central Pacific ocean. These little guys have developed a symbiotic relationship with the bio-luminescent bacteria Aliivibrio fischeri, which gave them a formidable radiant superpower. A. fischeri is horizontally transmitted throughout the E. scolopes population, and the bacterium stays for the delicious sugar solution produced within the E. scolopes’ body. E. scolopes are nocturnal, so the bacterium’s role really shines (quite literally, as the bacterium is bio-luminescent), when the sun sets. Gliding through the night hunting for prey and evading predators, E. scolopes secretes streams of A. fischeri bacteria acquired during the day, the bio-luminescence of the bacterium helping the squid blend in with the moonlit ocean surface.
There you have it. The next time you go out for calamari, please keep in mind that they were once fascinating creatures that once lit the ocean surfaces with their luminescence.