Dark Priming — Nocturnal Melatonin Failure Under Nighttime Warming Triggers Bleaching

Corals are famous for their colorful appearance, which actually comes from tiny algae living inside their tissues — a partnership that sustains most of the world's reef ecosystems. When ocean temperatures rise too high, this partnership breaks down in a process called bleaching: the coral expels its algae, turns ghostly white, and can die. Scientists have mostly focused on daytime heat as the trigger, but this hypothesis asks: what if the damage is set in motion the night before? Here's the proposed mechanism. Melatonin — yes, the same hormone that helps humans sleep — is also produced by both corals and their algae at night, and it acts as a powerful antioxidant, mopping up harmful molecules and essentially 'resetting' the cells' defenses before the next day's sun exposure. The hypothesis suggests that when nighttime ocean temperatures are elevated (a growing reality with climate change), the coral's melatonin system gets disrupted, depleting this critical chemical buffer. By the time dawn arrives and photosynthesis kicks off — generating the reactive, potentially damaging oxygen molecules it always does — the coral has no chemical armor left. What would normally be a manageable stress becomes catastrophic. This idea borrows from plant biology, where melatonin's role in nighttime stress defense is relatively well-studied, and transplants it into the coral world. It reframes bleaching not as a purely daytime heat problem, but as a failure of nocturnal recovery — a kind of 'dark priming' that makes the coral vulnerable before the stressful day even begins.

This is an AI-generated summary. Read the full mechanism below for technical detail.