Firefly Squid

InvertebrateJapan

24 Jul

Written By Alexander Julius Jensen

Watasenia scintillans

Each spring, thousands of firefly squid gather in Japan’s Toyama Bay and light up the water with their neon-blue bioluminescence. After laying and fertilising their eggs, they die. A year later, their offspring will return to do the same.

Sakura Season

A path of blossoming cherry trees in Osaka.

It's spring in Japan, and the cherry blossoms are completing their bloom. You've watched the tree canopies turn pink with sakura flowers, transforming parts of the bustling city into fairytale scenes. You walked the parks and riversides, as the gentle petals floated down like pink rain in slow motion. You savoured the subtle flavour of seasonal sakura snacks: taking bites of stretchy, light-pink mochi and sipping sakura tea. You gathered with others for Hanami, or "flower viewing", and now petals rest on everyone's clothes and in their hair. You watched as the last sakura petals relinquished their grasps and fell to the ground, marking the end of this ephemeral season — lasting two short weeks — and making way for the green leaves that will sprout in their stead.

Now you're in the city of Toyama, located on Japan's west coast, some 350 kilometres (~215 miles) northwest of Tokyo, known best for its glassware craftsmanship and as a historical centre of medicine. But it's the city's bay — the third largest in Japan — that you've come for. During winter, Toyama Bay shimmers with mirages known as "floating islands" off on the distant horizon. Spring brings a wholly different phenomenon to the bay. One that is, at the same time, dazzling and a little heartbreaking.

Watasenia scintillans

Watasenia scintillans is a small cephalopod. It grows to a length of 7 or 8 centimetres (3 inches), with a muscular cylindrical sheath that encases its body, known as a mantle, flanked by two side fins, and, at its base, eight runty arms and two tentacles — the arms are shorter and entirely lined with suction cups, while the longer tentacles only have suction cups at their ends.

Its home is the western Pacific Ocean around Japan, where it spends daylight hours in the dark depths of 200 to 400 metres (655–1,310 ft) — also known as the "twilight zone", a place with little to no significant sunlight. But as night falls, this shy, squishy creature rises to the ocean surface to hunt for small crustaceans and fish, ensnaring them with its hooked arms and tentacles. By the time dawn spills its first golden light onto the water, the squid has already fled back into the abyss.¹

This little cephalopod may spend its entire life hiding from the sun, but its world is not devoid of light. W. scintillans is more commonly known as the firefly squid because of its brilliant ability to light up the dark. Its body is bespeckled with over a thousand light-producing organs called photophores. In the pitch-black waters, it shimmers and sparkles, illuminating its tiny silhouette in neon blue. It can flash all its photophores in unison, like a flickering neon sign, or shift between patterns as if putting on a miniature light show. And in a way, that's exactly what it's doing: putting on a show for its aquatic neighbours, its intentions both romantic and malicious.

The myriad tiny creatures that float near the ocean surface at night — planktonic copepods, teensy fish, and even smaller squid — are easily entranced by pretty lights. From the darkness comes a sudden flash of blue; a dazzling light that blinks and oscillates in enchanting shapes and patterns. Taken in by the light, the tiny night creatures are stunned into inaction as ten wriggling limbs encircle them, snatching and dragging the helpless victims into the squid's mouth. The firefly squid is a frightening and cunning predator on the miniature scale, but the ocean is very large indeed, and home to some very large things — including predators much, much bigger than the firefly squid.

You'd think flashing bright blue against a dark ocean backdrop would be a conspicuous "come-eat-me" beacon. But the firefly squid actually uses its bioluminescence to hide from dangers, counterintuitive as that may sound.

Countershading is a widespread method of camouflage among aquatic animals. Think of the light underside, darker dorsal (upper) side pattern seen in many aquatic animals — most obvious in penguins and orcas, and less so, but still present in most fish, dolphins, and some seals. The light underbelly of a counter-shaded animal, viewed from below by a predator, appears to blend into the light coming from the ocean's surface, obscuring its silhouette and making it more difficult to spot. The firefly squid has no such permanent colouration. Instead of countershading, it employs counter-illumination: a camouflage that is identical in function but different in its mechanisms.

During the day, when the firefly squid hides in the twilight depths, it lights up the side of its body that faces down towards the ocean floor, and it keeps the side facing the surface unlit. Seen from below, its bioluminescence simulates the weak light coming from the surface, while seen from above, its unlight surface blends into the dark of the abyss. If subtle camouflage fails, the squid may try a brazen tactic: flashing its bioluminescence as wildly as possible in a bid to blind or startle the threat before whizzing away.

A Bay of Fireflies

One firefly squid, sparkling blue in a vast, black ocean, isn't all that dazzling — its bioluminescent light would hardly be bright enough to read by. But gathered in their thousands, the firefly squid turn the coastlines of Toyama Bay into a reflection of the sparkling night sky; the ocean "stars" burning a bright, electric blue. This heavenly spectacle occurs annually, typically between April and May, and only lasts a single, fleeting month. The usually solitary squid gather near the surface in droves and communicate via flashes. Each squid sparkles to attract a lover: males looking for females to lay the eggs, and females for males to fertilise them.²

As you lean over the railing of a fishing boat to watch the dances of these lovelorn squid, you're reminded of the Tokyo skyline at night, with its endless blinking lights, its neon signs and screens — it's like watching a city come to life beneath the waves.

Glowing firefly squid on the shores of Toyama Bay.

In Toyama, there is a museum — the Hotaruika, or Firefly Squid Museum — dedicated to these little squid. In the museum, you saw a firefly squid up close. You even held one gently in your hand and learned about its life history.

Born in spring, a firefly squid is swept to sea and spends its life in the open waters. The following spring, it makes its first and last journey back to the bay where it was born. After one last light show, the squid lays its eggs or fertilises the batch of another, and in doing so completes the annual cycle. Shortly after, the squid dies. As you walk the shoreline of the bay at night, you see thousands of floating bodies. They illuminate the waves that lap onto the sand, their blue slowly blinking out. It's the end of a thousand lives and the beginning of many thousands more. It's beautiful, and also a little sad.

Mujō

Mujō is a Japanese word that means 'impermanence' or 'transience'.

It is a concept with origins in Buddhism, stemming from the belief that nothing in our world is permanent; all things are in a state of constant change or transition. The acceptance of impermanence is considered an essential part of attaining happiness, with one of the most prevailing doctrines teaching that: to cling to the transitory aspects of our world ultimately leads only to dissatisfaction and suffering.

Buddhism is practised by around 46% of the Japanese population, but the influence of mujō on Japanese culture is even farther-reaching. It's not hard to see why such a concept would resonate here. The archipelago nation is a land undergoing constant, often extreme, changes — some beautiful and joyful, others destructive and terrifying — and these changes, more often than not, are completely out of our control.

*The Great Wave off Kanagawa* by Katsushika Hokusai.

Japan lies along the western edge of the Ring of Fire, a ring of volcanism and seismic activity that accounts for some 75% of Earth's volcanoes and 90% of all earthquakes. Every year, the country experiences around 1,500 noticeable quakes. The shifting earth jostles the mountains, sending landslides barreling down the slopes. Typhoons and tsunamis — meaning ‘harbour’ (tsu) 'wave' (nami) in Japanese — batter the country's coasts.

On the 11th of March, 2011, the most powerful earthquake in Japan's recorded history — a magnitude 9.0 - 9.1 — struck below the North Pacific, 130 kilometres (81 miles) east of the Tōhoku region. The quake created a tsunami, sending 40-metre (132-foot) tall waves sweeping through Sendai, Ishinomaki, Kesennuma, Rikuzentakata, and many more cities, towns, and villages. Kesennuma, a coastal city reliant on its fishing industry, was economically devastated. 90% of Rikuzentakata was destroyed. In total, over 450,000 people lost their homes. More than 15,500 people lost their lives. All in the course of a single day.

Imagine your life irreversibly changed, so unexpectedly, in so short a time, and by something completely out of your control. Such disasters are horrifying, and their consequences are horrific. It's only natural to be afraid of them. But does living in constant fear constitute living at all? Earthquakes and tsunamis, eruptions and typhoons, are very extreme reminders of the fragility and mutability of life.

Even in the absence of natural disasters, our lives are just as uncertain and fleeting, just less noticeably so. It is through a concept like mujō that we remind ourselves of that fact — not to induce fear, but as a reminder that we should never take the life we do have for granted.

The philosophy of mujō isn't an invitation to inaction. We do what we can do, we work on what is within our power — in the case of natural disasters, we create early warning systems, buildings that can withstand assaults, and response protocols always at the ready. Rather than an excuse for resignation, mujō is about making peace with the inherent uncertainty of life, which will always remain in some capacity, and finding contentment within change and impermanence.

Throughout Japan's cities and parks, its mountains and valleys, and along its coasts, there exists a different kind of mujō — one that you've experienced firsthand, if briefly, in the passing of spring. This is the kind of mujō that calls for appreciation. It is the cherry blossoms that bloom and fall in the course of two weeks — and they always fall, no matter how long you wish their beauty to last. It is the romantic parade of glowing squid beneath dark waves — the conclusion of thousands of year-long lives, a rejoicing finale for a generation of squid, and an event that illuminates Toyama Bay for a single spring month. This is the mujō of the beautiful and wonderful. It is the kind of change that allows us to appreciate, for often, it is only in something's absence that you realise how truly special it was. Whether it be a blossoming flower or a sparkling squid.

¹ Such daily movement between depths is known as 'diel vertical migration', practised by creatures ranging from tiny planktonic krill to behemoths like the megamouth shark, and heralded as the "largest synchronous migration on Earth".

² The firefly squid is a member of the class Cephalopoda — the cephalopods — along with squid, octopus, cuttlefish, and nautiluses. While many of these alien-esque animals are known for their colour-changing abilities, they're all believed to be colour-blind, with only one type of cone (colour receptor) in their eyes. That is, all except for the firefly squid.

While more thorough research is required into the specifics of this squid's vision, it's believed to possess complex eyes with three different types of light-sensitive cells (like ours), giving it the ability to distinguish different colours. Although the squid likely perceives the world quite differently from us, it is capable of seeing and appreciating the enchanting glow of its fellow firefly squid.

**Where Does It Live?**

⛰️ Depths between 200 and 400 metres (655–1,310 ft).
📍 Western Pacific Ocean

‘Least Concern’ as of 03 May, 2010.

IUCN

Size // Tiny
Length // 7 - 8 cm (3 in)
Weight // N/A
Activity: Nocturnal 🌙
Lifestyle: Social 👥
Lifespan: 1 year
Diet: Carnivore
Favorite Food: Planktonic creatures and other tiny sea life 🦐
Phylum: Mollusca
Class: Cephalopoda
Order: Oegopsida
Family: Enoploteuthidae
Genus: Watasenia
Species: W. scintillans

An individual firefly squid is a tiny critter — only some 7 or 8 centimetres (3 inches) long — and, in the light of day, unremarkable. Only in the dark of night or the depths of the abyss does it live up to its glowing namesake.
In the twilight zone, at a depth between 200 and 400 metres (655–1,310 ft), firefly squid use their blue bioluminescence to hide. They glow in the dark to hide? Counterintuitive as it may sound, yes.
Just like many sea animals have darker uppersides and lighter undersides (known as countershading), this squid will light up its underside, while keeping its upperside dark. When seen from below, its glowing belly blends with the light filtering down from above, while its dark upperside makes its silhouette vanish into the abyss when viewed from above. This clever camouflage is called counterillumination.
If it is spotted by a predator, the squid may attempt a bold tactic: flashing its bioluminescence as wildly as possible in a bid to blind or startle the threat before whizzing away.
Each night, firefly squid migrate from the depths to the ocean surface to hunt planktonic copepods, tiny fish, and even smaller squid — all attracted by the squid’s flashing lights.
Finally, every spring, usually in April or May, thousands of firefly squid flock to Toyama Bay in Japan for a spectacular breeding event and a final, glowing light show that illuminates the shore. Then they all die, leaving their offspring to continue the cycle the following year.