Radiolab – "The Glow Below"

Date: October 31, 2025
Host: Molly Webster (WNYC Studios)
Featured Guest: Dr. Edie Witter, Oceanographer and Deep Sea Explorer

Episode Overview

In "The Glow Below," Radiolab dives into the mesmerising world of bioluminescence in the deep sea, guided by deep-sea explorer Dr. Edie Witter. What begins as an inquiry into anglerfish detours into an illuminating journey through the ocean’s mysterious twilight zone—where light, far from extinguished, literally comes alive. Witter recounts her decades of pioneering research, sharing jaw-dropping encounters with glowing creatures, the science behind their light, and why bioluminescence may be the most important and underappreciated form of communication on Earth.

Key Discussion Points & Insights

Bringing Light from the Depths

• Early Encounters:

  • As a graduate student in the 1980s, Witter was part of a project retrieving live deep-sea animals using a thermally insulated net ("cod end"), sparking her fascination with oceanic bioluminescence.
  • First encounter: a bright red shrimp that "squirting neon blue light out of tubes on either side of its mouth" ([01:00]).

• On the Experience of Holding Bioluminescence:

  • "It was cold light, and it was brilliantly blue." – Edie Witter ([02:00])
  • The effect was so remarkable that Witter committed the next 40 years to studying deep-sea light.

Exploring the Deep in Submersibles

• First Dive Experience:

  • Witter describes her first trip down 800 feet in an astronaut-like suit called 'W.A.S.P.' ([04:06]), experiencing vivid 'fireworks' of bioluminescent displays after turning off the lights:
    • "I was instantly in the center of this fireworks display...sparkles and glows and squirts. All of it different shades of brilliant, brilliant blue." ([05:08])

• Why Blue?

  • Blue is the color that travels farthest through seawater, explaining the predominance of blue bioluminescence ([05:52]).

• Seeing Without Seeing:

  • Bioluminescence only visible with lights off: "You have to turn the lights off to actually see what you want to see." – Molly Webster ([06:28])
  • With lights on, few creatures are visible, complicating research and observation.

Functions of Bioluminescence in Marine Life

• Multiple Purposes: ([07:51])

  • Finding Food: Some fish, squid, and shrimp have light organs near their eyes, used like flashlights.
  • Attracting Mates: Specialized light organs or displays signal to potential partners.
  • Defense (Burglar Alarm): Flashes of light attract larger predators, potentially scaring off attackers.
  • Camouflage (Counterillumination):
    • Animals mimic the downwelling sunlight with light from organs on their bellies.
    • Example: The cookie-cutter shark’s perfect 'cloaking device' ([09:03]).
    • Light intensity can be rapidly adjusted to match changing sunlight (i.e., clouds overhead).

• Unknown Sensing Mechanisms:

  • "Some of them actually have a light organ above their eye that they can see... But others we’re not sure how they do it." ([09:38])

Deep-Sea Oddities: The Bearded Sea Devil

• Convoluted Light Organs:
  • The bearded sea devil anglerfish:
    • Has two types of bioluminescent organs—one chemical on its chin, one bacterial on its forehead. ([10:16])
    • "The one coming out of its chin is intrinsic chemistry... But the one coming up out of its forehead is bioluminescent bacteria." – Edie Witter ([10:50])
  • Fish acquire light-producing bacteria from environment and control glow by controlling oxygen to the bacteria, sometimes via a mechanical shutter ("like an eyelid") or by retracting the organ into their head ("like the headlights on your Lamborghini") ([11:49], [12:00]).

Evolutionary Mystery: Why Make Light?

• The Photolyase Hypothesis: ([13:27])
  • Early bioluminescent bacteria’s glow conferred a UV-protection advantage:
    • Light activates photolyase, an enzyme that repairs DNA damaged by sunlight.
    • "So the selective advantage had nothing to do with vision initially, it had to do with protection against UV light." – Edie Witter ([15:05])
  • Over evolutionary time, as creatures moved deeper, light’s role shifted from a protective mechanism to one of communication and survival.

The "Flashback Phenomenon" & Participating in the Deep

• Discovery in the Deep Rover: ([15:51])

  • By turning off all light and waiting, Witter observed that triggering thrusters or toggling lights caused surrounding particles/organisms to emit light back—a coordinated flash (“flashback phenomenon”).

• What’s Flashing?

  • Suspects that bioluminescent marine snow—organic matter coated with bacteria—is the main culprit ([17:18]).
  • Some marine worms (e.g., tomopterid worm) can also produce unique bioluminescence.

• Purposeful Light:

  • "The bacteria glow in order to be eaten... to be reintroduced into the food-rich environment of a fish gut." – Edie Witter ([19:30])
  • Implies a symbiotic "dance": by disturbing the water, Witter becomes part of the ecosystem’s bioluminescent communication.

• Emotional Impact:

  • "I feel a tremendous sense of awe... Our survival has been to explore the world around us and share that information." ([20:05])

Stories & Sensory Memories

• Personal Accounts:
  • Molly recounts her own childhood encounter with pond-edge bioluminescence, highlighting its power to awe even outside the ocean ([21:33]).
    • "It was all lit up...glowing...I went back inside and woke my parents up, and we all marched down to the pond and just stood there and looked at this glowing." – Molly Webster ([21:33])
  • Edie stresses the deep, almost mystical impact these experiences have on people:
    • "People that have had interactions with bioluminescence often rank them as their most meaningful lifetime experiences." ([22:05])

Bioluminescence: The First Language?

• Universal Communication:
  • Edie provocatively suggests bioluminescence may be "the most common form of communication on the planet" ([22:59]).
  • Much remains unknown:
    • "There have been a few times when I've communicated with luminescent animals...I was pretty sure it was something sexy." – Edie Witter ([23:23])
  • Communication isn’t fully understood; observations are "guesswork" due to lack of direct study.

Notable Quotes & Memorable Moments

| Timestamp | Speaker | Quote / Moment | |-----------|----------------|--------------------------------------------------------------------------------------------------------------------------------------------| | 01:00 | Edie Witter | "...bright red shrimp about the size of a hamster. And it was squirting neon blue light out of tubes on either side of its mouth." | | 05:08 | Edie Witter | "I was instantly in the center of this fireworks display...All of it different shades of brilliant, brilliant blue." | | 07:08 | Edie Witter | "To use that much energy...there was no question this had to be about life or death." | | 10:50 | Edie Witter | "...the one coming up out of its forehead is bioluminescent bacteria." | | 15:05 | Edie Witter | "...the selective advantage had nothing to do with vision initially, it had to do with protection against UV light." | | 19:30 | Edie Witter | "The bacteria glow in order to be eaten. They want to be eaten...it is to their advantage to be eaten because then they are reintroduced..." | | 20:05 | Edie Witter | "I feel a tremendous sense of awe...our survival on the planet has been to explore the world around us and share that information." | | 22:05 | Edie Witter | "...people that have had interactions with bioluminescence sometimes...rank them as their most meaningful lifetime experiences..." | | 22:59 | Edie Witter | "...it may be the most common form of communication on the planet. Partly depends on how you define communication..." | | 23:23 | Edie Witter | "There have been a few times when I've communicated with luminescent animals...I was pretty sure it was something sexy." |

Timestamps for Key Segments

• Opening & Edie’s First Bioluminescent Encounter — [00:19]–[02:30]
• First Submersible Dive & the "Fireworks Display" — [03:51]–[06:28]
• Purposes and Mechanisms of Bioluminescence — [07:05]–[09:57]
• Evolutionary Origins of Bioluminescence — [13:27]–[15:06]
• The "Flashback Phenomenon" and Marine Snow — [15:51]–[18:53]
• Human Connection & Awe — [20:05]–[22:05]
• Bioluminescent Communication — [22:52]–[24:39]

Tone & Style

The conversation is rich with a sense of wonder, humor, and curiosity. Edie’s awe at nature’s cleverness is infectious, and Molly’s questions reflect an accessible, wide-eyed amazement that invites listeners to join the journey.

Further Exploration

• Edie Witter’s work: Documentary “A Life Illuminated” (Sandbox Films)
• Other Radiolab episodes: "Octomom" and "The Darkest Dark" for more deep-sea stories

This summary captures the essential science, storytelling, and emotion of "The Glow Below," for both longtime Radiolab fans and new explorers of the luminous undersea world.