I really like this beautifully-written excerpt about an amazing part of God's creation from Robert Finch's book The Outer Beach, pp. 61-62.
The tide is approaching its high. The seethe of incoming foam laps and sloshes just below the wrack line on the upper beach, sliding back toward the dark breakers in a bubbly, sucking withdrawal. The breaking crests of the waves and the foamy swash edge appear to be outlined with a faint phosphorescence, but it is hard to tell in the obscurity of the fog. The wrack line itself – a knotted tangle of rockweed, dulse, mermaid’s tresses, broken claws and shells – is speckled with thousands of tiny, pale, yellow-green coals of light. This is bioluminescent plankton, hordes of diatoms, dinoflagellates and copepods that in summer fill vast stretches of ocean with their cold, chemical glow – a sort of Aurora maritima – so that ships plowing through these living shoals of light leave wide wakes of flickering fire behind them.
Some of the larger glowing particles in the wrack line are hopping about, like sparks from resinous kindling. Shining my flashlight on them, I see the bouncing forms of sandhoppers, or beach fleas – miniature, shrimplike crustaceans about a third of an inch long, with huge eyes and pearly white bodies. By day they live in burrows on the upper beach, coming out at night to feed on the tide’s leavings. They ingest the tiny phosphorescent plankton, and their semitransparent bodies begin to glow like miniature jars full of fireflies.