The Mystery of Underwater Crop Circles, Explained

By Lisa Raffensperger | August 15, 2013 2:39 pm

underwater crop circle

They’ve been called the crop circles of the ocean floor—seven-foot diameter patterned circles that were first spotted in 1995 off the coast of southern Japan. But their origin was an enigma, and local divers termed them “mystery circles.”

The mystery persisted until 2011 when the culprit, a male pufferfish just five inches long, was finally caught in the act. And recently scientists studied the process of how the species creates these elaborate designs in order to woo females.

Finned Diggers

The research team observed a total of 10 construction events carried out by somewhere between 4 and 8 males. (Pufferfish don’t have very memorable faces, apparently.) Males spent seven to nine days building their respective circles by repeatedly swimming in and out of the circle, using their fins to dig valleys in the sandy bottom.

Aesthetics were clearly important. The spirograph pattern was meticulously created and males were observed decorating the peaks with shell and coral fragments. But the design had a practical purpose as well: the male’s swimming pattens stirred up fine sand particles and pushed them toward the middle of the circle, which served as the actual nest.

This was the part of the circle where he entertained lady callers. When a female pufferfish approached the circle, the male stirred up the sand in the middle and darted back and forth through it. If she judged him a suitable mate, she would lay her eggs in the sandy central zone, the researchers reported last month in Scientific Reports.

Build and Rebuild

Scientists say it’s likely that the quality of the circle helps determine a female’s mate choice, though they have yet to demonstrate how. But once mating is completed, the male ceases his upkeep of the circle, and after the eggs hatch, he abandons the nest altogether.

But after all that effort, you may ask, why not just reuse his earlier circle? The authors speculate that the male’s forceful wooing depletes the area of its fine sand particles, which are necessary for the next round of egg-rearing. And then it’s back to the drawing board for these amorous artists.

(Top image: YouTube screenshot, source)


CATEGORIZED UNDER: Living World, select
MORE ABOUT: fish, ocean
  • C.R.K.

    So cool! I <3 science!

    • Heimdall222

      What does “<3" mean?

      Details, please!

      • Andrew C Livingston

        It’s supposed to look like a heart. So, it means I heart science.

        • the

          Lmao clown. Oh so sad

          • Andrew C Livingston

            What? That’s what it means. Blessent mon coeur d’une langueur monotone…

  • isnamthere

    I’d like to see one started by a puffer fish and not just a fish swimming around in an existing circle.

    • Barrington Lloyd

      Then you should become a marine biologist and study some yourself instead of downplaying this amazing video.

      • isnamthere

        Your suggestion is ridiculous. People read about all sorts of topics that they are interested in while not being trained experts in the field. How can simply requesting evidence for a scientific claim automatically put the burden of proof on the reader? The video does not provide proof of puffer fish being responsible for these circles, as cute as they may look swimming around in one. I don’t necessarily deny the claim, nor do I fully believe it at this point. I’ll simply reiterate my initial comment: I’d like to see one started by a puffer fish. And as part of the intended audience for this piece, I don’t think it’s incumbent upon me to go out and become a marine biologist to ask for proof.

        • Barrington Lloyd

          It’s pretty clear from the video that the pufferfish is contributing to the maintenance and design of the circle as it stands. Not only is it swimming with purpose back and forth across the circle, it dips and swells along with the design of the circle itself. It kicks up sand in specific valleys instead of just swimming through randomly.

          More importantly, there is no reason you should expect to see a fully-made circle from start to finish as proof. The fact that this study was done by scientists, with the scientific method, should be enough if you really are interested in the work. The video is a bonus, and I agree that it would be cool to see a whole circle made from scratch on video. However, to make the suggestion that you won’t believe it until you see the video, even though it’s been studied and reported by reputable scientists, is short-sighted.

        • Jennifer Symonds

          What about Bower birds they decorate their bowers beautifully in order to attract a mate or are doubtful about them as well,Nature never ceases to amaze me, & this just something else I shall add to my list of amazing (natural) list.

        • Alan

          Click on the red “reported” link after the word researchers in the above article. It will take you to the scientific paper where proof is provided.

          • John Seychel

            hi Alan

        • draven

          wow i have know

        • Enric Martinez

          OK, post a video if an UFO swimming back and forth in the circle 😉

    • Heimdall222

      Hey, folks, let’s not encourage the mentally-deficient.

      Or maybe you folks don’t recognize a troll when you see one?

    • draven

      i know right

  • Ryan Deadpooln

    That is wild.

    • Heimdall222

      What is wild?

      Details, please!

  • Heimdall222

    You don’t need to laser-guide your loogies!

    Simply pull your head out of where the sun don’t shine, and look at where you’re aiming.

    But wait.

    If you pull it out, you’ll have to see the world as it actually is.

    Which will mean that those voices you’ve been hearing in your head aren’t real.

    Or…are they?

  • Byron Winchell

    Is this behavior an example of “Convergent evolution ” when compared with the similar behavior of Bowerbirds? Bowerbird nests include use of perspective to make a smaller nest look bigger (for less effort).

    “Bowerbirds /ˈbaʊərbɜrd/ make up the bird family Ptilonorhynchidae.They are renowned for their unique courtship behaviour, where males build a structure and decorate it with sticks and brightly coloured objects in an attempt to attract a mate.”

    One thing is certain, when something really stupid is going on, it’s because the females have imposed it as a test. The stupid part is what the males are for doing it as the price of reproduction. Oh no, I sense my line dying out for lack of a successful mating . . . .

    • Byron Winchell

      Apologies to Jennifer Symonds who had this idea more than 15 hours ago.

      • Jennifer Symonds

        Great minds think alike (& I’m not finishing that one as it includes me!!) [My eyesight’s not too good but are you using a pic of the late great Groucho? My favourite quote of his (from a student! note book cover “I worked myself up from nothing to a state of extreme poverty”!] Nothing to do with puffer fish or bowerbirds unless you think of me as having a mind like a grasshopper — so it’s still wild life related!!??!!!

        • Byron Winchell

          Groucho he was, and avatar of mine he now is.

          Well, my apology was necessary as there were only about 15 comments to review, not like when I go a-trolling on Yahoo. If I had, I wouldn’t have tried out my mangled notion of “convergent evolution” on a behavior trait no less. You had seen the link.

          Um, speaking of behavior traits, I’m trying to remember if the common SW US packrat attempts to attract a mate by hoarding ‘found’ objects . . . “look! a shiny object!” Just think what’s going through the female packrat’s mind, “Wow, he has a lot of STUFF, surely he is the most fit to be the father of my litter.” I assumed w/o bothering to look anything up that the theft and hoarding is the behavior of the male of the species.

          Yes, there is a decided grasshopper mentality in my commentary. Can’t call it thinking, more like stream of consciousness.

          Have a nice convergence.



          • Jennifer Symonds

            Magpies also nick shiny things, & I like to use a lot of bling on my cards!! though I don’t nick it!! Consciousness streaming — if only I’d thought of that when a teacher (eons ago it seems) told me I had a grasshopper mind it sounds more — er — intellectual put that way !!!

  • Secret Island

    Swimming around in circles: Sounds like the dating game to me. May the circle go unbroken, but abandoned is ok. Who’s going to take care of the kids?

  • Jennifer Symonds

    My cat’s an alien, she uses mind control when she thinks she’d rather have my food to what she’s got — & it works!!???!!!

    • John Seychel

      My thought too. My counselor was telling me of something I was aware of, and that is why do dogs and cats know when the master is going to feed or go for a walk. It hit me that the evaluation of these creatures go back millions of years, and way before spoken language. But they are pack animals and have been, so why do we think they have these amazing abilities to sense when we are going to have activity with them? Well it hit me that they may just be talking to us in their own way and we pick it up without knowing we have the same ability but have lost it because of spoken language. They tell us when they are hungry or need to go out and always know and seem to be waiting on your reaction to their call.



  • nolan


  • nolan


  • draven

    omg sooooooo cool

    • draven


  • Daniel Aarden

    I truly believe in crop circles.

  • vetiarvind

    I’ve always held all sentient beings had an innate capability for inspiration. Glad I’m a vegetarian.

  • Clippingimages

    Awesome writing style!

  • CSBlum25

    Discovered in 2011!


Discover's Newsletter

Sign up to get the latest science news delivered weekly right to your inbox!


See More

Collapse bottom bar