A biolight puzzle

We sailed three weeks straight from New Caledonia to Darwin, and sometimes when you stay at sea for weeks at a time, the world becomes strange. In early September the prevailing winds over Australia’s Top End were light, and it took six days after running the Torres Strait before we saw Australia again. Two large islands, Bathurst and Melville, guard the Top End’s capital. We chose to run the Dundas Strait east of these Tiwi Islands and so theoretically make port quicker. After eight hours of rolling through muddy water making little progress in light winds against current swirls that formed and unformed across our path, we turned around, opting for a less complicated night at sea.

I take the first night watch. The moon was down, the night placid with a 6 to 8 knot wind. An hour before I would get to sleep, the sea was lit, as my log notes say, “by phosphorescence (sic) the size of saucers. Can see the horizon. Like sailing on the stars. Thought it was reflection from the tricolor.” Fifteen miles from land the water was only 86 feet deep. The effect was of a carpet of white, the lights evenly spaced, some deep some on the surface. They didn’t flicker or appear and disappear, they were simply there. A life hidden in the dark ocean, away from human eyes. “Strange ocean.”

Going over the top of the Tiwis meant we spent a final eight hours motorsailing into screaming winds, the last southeast blow of the season. We anchored downtown off Stokes Hill Wharf where oil rig tenders, tourists, and sunset cruise boats vied for space, and one evening after beers at a wharf restaurant I approached a research vessel to ask about the stationary lights. The man on deck didn’t know the phenomenon but suggested it might have been algae. Had we seen long strands of brown yuck on the water? Yes…

Many organisms in the sea emit light, and surface luminescence is common in tropical waters. Bacteria, jellyfish, squid, even fish and crustaceans, produce light by biochemical reaction. Dinoflagellates are fragile, transparent animals which I’ve often seen floating beneath the electric-blue deep ocean surface on calm days. They’re responsible for most of the brilliant light displays, like the greenish-white trail Oddly Enough’s rudder makes. Jellyfish emit larger, brighter points of flashing light. But all this light is produced when the animals are disturbed and quickly winks out.

Thirty-five miles east of Cape Van Diemen, the sea glowed to the apparent horizon, in long sheets of white ten yards wide separated by black. Calm wind, no waves, nothing agitating it. The striped effect could concur with streams of algae, which appear as the waters off Australia heat up. Are any marine biologists here among the readers? This incident is an unfinished puzzle for me!

By Ocean Navigator