Drag through the surf. Every spark is one cell of Noctiluca scintillans, a plankton that flashes when the water around it is pushed. Stir the same patch again and again and it tires, then slowly recovers. Fish show up only by the light they kick up.
cell 0.2–2 mm · one flash ≈ 0.1 s · dinoflagellate light peaks near 472 nm the light comes from luciferin and luciferase, set off when the water moves