Yet another random plot thread. Coral reproduction culminates in a marvelous display. "Synchronous spawning is very typical on a coral reef and often, even when there are multiple species present, all the corals on the reef release gametes during the same night. This synchrony is essential so that male and female gametes can meet and form planula. The cues that guide the release are complex, but over the short term involve lunar changes, sunset time, and possibly chemical signalling.^[9] Synchronous spawning may have the result of forming coral hybrids, perhaps involved in coral speciation.^[12] In some places the coral spawn can be dramatic, usually occurring at night, where the usually clear water becomes cloudy with gametes."

What if a plague learned how to bide its time, or a parasite was sentient. Such that the population of a planet became infected or infested, and passed the infection/infestation around by sex or birth, and the sentient hive mind of the plague/parasite waited passively for many generations for the majority of the population to be infected before triggering the active form of the plague/parasite. At which point a majority of the planet would drop dead, or be physically altered (as usual into some monstrosity).

Plot point would be that a character discovers this plague/parasite after a significant percentage of the planet has been infected. What steps could be taken if it were incurable? Genocide? Quarantine?