The sparkling deep

It's tempting to see bioluminescence as an oddity, one of those rare eccentricities of life on earth. And, on land, maybe that's true. But our planet is mostly water, and out in the open ocean bioluminescence is utterly commonplace. Creatures of all shapes and sorts sparkle and glow, glitter and pulse. But what are these displays for? Why did they evolve? How did light become the currency of the deep?   My guest today is Dr. Sönke Johnsen. Sönke is a Distinguished Professor of Biology at Duke University, where he and his research group study the visual ecology of the ocean. He's the author of a number of books: most recently Into the Great Wide Ocean, about life in the pelagic realm, and The Radiant Sea, a photographic tour of bioluminescence and color, written in collaboration with Dr. Steven Haddock.  Here, Sönke and I talk about the open ocean: the most common habitat on our plant, yet one that many people will never experience. We consider the curious distribution of bioluminescence— rare on land, exceptionally prevalent in the ocean, and all but absent in freshwater. We talk about how bioluminescence seems to have evolved—many, many times over in fact. We survey the functions of making light in the deep—from counter-illumination to courtship to revenge. Finally, we consider what Sönke takes to be the biggest remaining puzzle about bioluminescence at sea.  Alright friends, if you're enjoying *Many Minds*, we ask (humbly) if you would think about rating us, reviewing us, leaving us a comment, boosting us on social media, or perhaps haranguing your friends—relentlessly—until they give us a listen.  Without further ado, onto my conversation with Dr. Sönke Johnsen. Enjoy!    *Notes* 3:30 – The scientific report by Dr. Johnsen and colleagues describing the bioluminescent octopus, *Stauroteuthis syrtensis*.   12:00 – A popular article on the bristlemouth. The article reports a scientists estimage of "as many as a dozen \[bristlemouths] per square meter of ocean." 15:00 – A recent discussion of the "burglar alarm hypothesis."  18:00 – The website for the Johnsen Lab at Duke University.  24:00 – A chart and discussion of the depth zones of the ocean. 29:30 – A study by Séverine Martin and Steven Haddock quantifying the prevalence of bioluminescence at different depths. A popular write-up of the same study.  33:00 – A popular article on vertical migration in the ocean, also called "diel vertical migration." A recent scientific study of the phenomenon.  39:00 – A recent article on the evolution of bioluminescence.  45:00 – For detailed scientific discussion of the physical basis of bioluminescence, fluorescence, and other phenomena we discuss, see Dr. Johnson's book, The Optics of Life.   52:00 – For previous episodes on the uses of sound in the animal kingdom, see here and here.  For our previous episode on electroreception and electric ecology (including in marine organisms), see here.   57:00 – For more on the functions of bioluminescence, see here. For a report of a recently discovered function of bioluminescence, see here.  1:03:00 – An article by Dr. Johnsen about the different colors of bioluminescence present in the deep sea. 1:05:00 – A video of ostracod displays.   1:08:00 – For our recent episode on cave art, see here. 1:16:00 – For our earlier episode on firefly synchronization, see here.     *Recommendations* Website and review article by Steven Haddock The lab of Todd Oakley Below the edge of darkness, Edie Widder   *Many Minds* is a project of the Diverse Intelligences Summer Institute, which is made possible by a generous grant from the John Templeton Foundation to Indiana University. The show is hosted and produced by Kensy Cooperrider, with help from Assistant Producer Urte Laukaityte and with creative support from DISI Directors Erica Cartmill and Jacob Foster. Our artwork is by Ben Oldroyd. Subscribe to *Many Minds* on Apple, Stitcher, Spotify, Pocket Casts, Google Play, or wherever you listen to podcasts. You can also now subscribe to the Many Minds newsletter here! We welcome your comments, questions, and suggestions. Feel free to email us at: manymindspodcast@gmail.com. For updates about the show, visit our website or follow us on Bluesky (@manymindspod.bsky.social).