It’s likely you’ve never seen a Hawaiian bobtail squid. That’s because they’re nocturnal — and smaller than your thumb.
The invertebrates are native and endemic to Hawaiʻi and live in shallow reef flats. They’re reddish or brown in color, have eight arms and might call to mind a baby squid or octopus.
But, they’re very different from what many people recognize as heʻe.
This tiny creature has some pretty amazing characteristics. Hawaiian bobtail squids have a special, symbiotic relationship with a glowing bacteria called Vibrio fischeri.
The squid provides a cozy home inside their bodies for the bacteria. In return, the bacteria allow the bobtail squid to produce light from a specialized organ. However, it’s not just a general luminescence.
“The symbiosis allows them to counter illuminate, so they're able to put light out from their dorsal side, or their belly side, that matches the amount of moonlight coming out during a given night," said graduate researcher Hannah Osland.
"They're able to adjust it so that if you're a predator that's kind of on the ocean floor swimming around at night and you were to look up and there's a bobtail squid there, theoretically, it'd be putting them out the amount of light that matches the moonlight so it would disrupt the bobtail squid’s shadow, so then you wouldn't be able to see it," she said.
Osland recently finished collecting samples from Hawaiian bobtail squid in several locations on Oʻahu and on Molokaʻi. The species’ luminescence has been well studied in labs, but not much is known about their lives in the wild.
She’s hoping to shed a little more light on the species.
Full of light — and mysteries
Previous research conducted about 20 years ago indicated something Osland wants to explore further. Bobtail squid populations from two different Oʻahu sites seemed to show genetic or morphological differences.
Osland is pursuing the possibility that bobtail squid could have distinct characteristics based on where they live. She’s also working to get population estimates. She said right now, no one has any idea how many Hawaiian bobtail squid exist.
Longtime Molokaʻi fisherman and boat captain Clay Ching said he used to take his kids out on nighttime nature walks along the shoreline at low tide. That’s when they’d sometimes find bobtail squid.
“Usually the ones you see are like, your baby fingernail kind of thing. They’re so cute, just real tiny. So that's why the kids always found them, because they got good eyes," Ching said.
"You want to go on a night that’s not windy, so the water is just real still. Walk out about 100 feet from shore, that's usually where we find them," he said.
Osland said their luminescence isn’t actually visible to humans looking from above because light is emitted from their dorsal, or underside. During the day, they’re even harder to spot, as they hide buried in the sand.
Osland’s research won’t wrap up until later this year, and there will still be lots of mystery surrounding the species, their behavior and where and how they live.
But in the meantime, Hawaiian bobtail squid will continue to swim under the moonlight, casting no shadows.
