As part of its ongoing efforts to promote every single Pokémon out there, The Pokémon Company has shared special content dedicated to Staryu:
Did you know? If you visit a beach at the end of summer, you’ll be able to see groups of Staryu lighting up in a steady rhythm. Fish Pokémon nibble at it, but Staryu isn’t bothered. Its body regenerates quickly, even if part of it is completely torn off.
Source: The Pokémon Company