Penn Professor Alison Sweeney explains the mysterious sex lives of corals


    Imagine – a full moon over the open ocean.  If you think that sounds romantic, you’re not alone.  Apparently corals think so too.  

    Imagine – a full moon over the open ocean.  If you think that sounds romantic, you’re not alone.  Apparently corals, the tiny sea creatures who build colorful reefs, think so too.

    In our regular segment “So, What do you do” where lay people interview scientists about their work – we met Alison Sweeney an assistant professor in Physics and Astronomy at The University of Pennsylvania. 

    Sweeney was interviewed by Shauna Small, a school psychologist in Philadelphia and Camden and founder of Agents Promoting Educational Change. Their discussion gave us a peek at the sex lives of corals. 

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    Since Professor Sweeney teaches and runs a lab in the Astronomy and Physics department at Penn, an obvious question from Shauna was whether Sweeney was an astronomer or a physicist, or both.

    Turns out Sweeney is neither. Her background is in biology and she has a PhD in evolutionary biology.  Her lab is spearheading a unique collaboration between biology and physics in the hopes that new discoveries in “synthetic biophysics” will emerge.

    “I know enough physics to know where the interesting physics happens within biology,” says Sweeney.  “I can now have immediate access to physicists on these cool biophysics projects that we find.”

    Bringing a biologist into the world of physics is new for the university.  

    “Penn has done a very cutting edge and brave, boundary breaking thing hiring a biologist to work among the physicists,” says Sweeney.  But there are places where the disciplines overlap.

    One of the things that Sweeney and her lab are investigating is how environmental color and light affect behavior in marine animals. Her work has led to some surprising findings about coral spawning.  Her  research may have unlocked the mystery of  how the millions of tiny sea creatures, living on miles and miles of reefs manage to release egg and sperm into the open ocean once a year, within a ten-minute interval.   

    Having all corals spawn within the same ten minutes increases the possibility for egg and sperm to meet, allowing procreation.  For Sweeney, the question was, how “these brainless animals know precisely which ten minutes of the year to release their reproductive output”.

    She found that the lunar cycle may be the key.  “We do know that the corals will tend to spawn three or four nights after the full moon”, says Sweeney. Following a full moon’s subtle color variations in the night sky may cue the corals to their collective spawning date.

    “Every twilight past the full moon gets bluer and bluer and bluer”, says Sweeney.  “There’s this whole color process in the sky, that if you were a coral, it would make a lot of sense to pay attention to.”

    Aside from coral, Sweeney has studied the color camouflage techniques of squid and giant clams.

    “We are just beginning to understand that this color complexity can actually have a lot of important biological ramifications.” 

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