Full moon rising. You know what that means: Coral making whoopee?
This is Sandra Tsing Loh with The Loh Down on Science.
Shallow-water coral live in large, isolated clusters. Yet once a year, they spawn. All at once. Right around the full moon.
How do millions of individuals, miles apart, synchronize their behavior without communicating? They can detect seasonal changes, so know roughly when it's about "that time" again.
But they have no voices, no eyes, no brains. How do they know "tonight's the night"?
Alison Sweeney of UC Santa Barbara thinks the night is different from all other nights because of ... twighlight.
When the moon's full, it rises right at sunset. The next evening? It rises almost an hour later. During that twilight hour between orangey sunset and pale pinkish moonrise, the sky goes a deep indigo color.
Many invertebrates lacking eyes are nevertheless affected by environmental color changes, because their bodies contain opsins ... light-sensitive proteins. Does the coral somehow use that distinctive dusky blue hue as a cue?
Researchers aren't sure yet ... but isn't it romantic!
The Loh Down on Science, online, at lohdown.org. Produced by 89.3 KPCC and the California Institute of Technology, and made possible by TIAA-CREF.
Follow us on Twitter at LohDown.