1986 "First Edition: May 1986" stated on copyright page; Del Rey Book publishers, New York; hardbound; very good condition with unmarked pages; dust jacket quite good with minimal wear.
 
Description -
Just a few islands in a planetwide ocean, Thalassa was a veritable paradise—home to one of the small colonies founded centuries before by robot Mother Ships when the Sun had gone nova and mankind had fled Earth.

Mesmerized by the beauty of Thalassa and overwhelmed by its vast resources, the colonists lived an idyllic existence, unaware of the monumental evolutionary event slowly taking place beneath their seas...

Then the Magellan arrived in orbit carrying one million refugees from the last, mad days on Earth. And suddenly uncertainty and change had come to the placid paradise that was Thalassa.