Natures wonders: bacteria cause milky seas (Introduction)

by David Turell , Thursday, November 04, 2021, 12:47 (903 days ago) @ David Turell

Still not fully understood:

https://nautil.us/issue/108/change/trillions-of-bacteria-are-screaming-with-light

"tales of seas that glow have popped up alongside mermaids and dragons in nautical lore throughout the ages. While these creatures of fiction appear in many different guises, the appearance of glowing seas is remarkably consistent.

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"Gathering over 200 accounts of milky seas, they discovered that these massive glowing patches, which would often last for days, were most common in the northwest Indian Ocean and Indonesian waters and occurred most frequently between January and March. Knowing roughly when and where milky seas were most likely to occur, the team next looked for them with satellites equipped with an instrument called the Day/Night Band—a new generation spaceborne low-light imager capable of sensing light roughly 10,000 times fainter than reflected moonlight.

"The “aha” moment came to Miller while flipping through these new images. “I was looking for clouds masquerading as milky seas when I stumbled upon an astounding event south of the island of Java,” he says. Searching additional images from 2012 to 2021, the team discovered 12 events that matched their strict criteria for milky seas—a lot of things can resemble a milky sea from space, says Miller—that occurred approximately one every eight months. The smallest of them was one hundred times the size of Manhattan.

"But what caused the sea to glow in the first place?

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"Vibrio harveyi bacteria “scream” to be eaten. They can live adrift in seawater but also feel right at home in the guts of fish. Normally these bacteria light up only when they’re living on clumps of dying and decaying algae—biological debris that scientists informally call marine snow—and only when they’re clustered in large numbers. When they’re packed together tightly enough on these clumps, they begin to glow in a kind of community effort to be collectively consumed, like a living fishing lure. In fact, this is why dead fish sometimes glow, as bacteria illuminate their once-living hosts.

"When a single bacterium floats alone in the ocean, lighting up would be a waste of energy. Its light would be so small it would essentially be invisible. But instead imagine that it’s not one bacterium but a million, all crowded together as if on a piece of marine snow. Like concertgoers cracking thousands of glowsticks in unison, suddenly a whole field alights with myriad luminous wands.

"Bacteria have a way of synchronizing their illumination via a process called quorum sensing. Each bacterium releases a small amount of a chemical signal into the surrounding water. As long as the signal is dilute, a bacterium will assume it’s alone. But as the population of bacteria increases, the signal grows stronger, until eventually it gets so strong that all surrounding bacteria sense it. The beat drops, the concert starts, and glowing bacteria light up the night ocean. (My bold)

"Why Vibrio harveyi collectively glow in such large numbers is still a mystery, but team member Steve Haddock, a marine biologist at the Monterey Bay Aquarium Research Institute, has some ideas. Haddock thinks their screams may be a kind of accidental cross-wiring. Normally all this would be happening atop marine snow, but if the Vibreo harveyi population grows too dense, it may set off this chain reaction at the surface, rather than on marine snow. Essentially, the bacterial populations get so thick at the surface that each bacterium think it’s a part of a dense colony ready to be eaten.

"Milky seas are most likely to occur in areas that are warm, sundrenched, and—unlike many tropical waters, which are comparatively clear and nutrient poor—full of nutrients. In these areas deep water wells up from the abyss to the surface. This deep water brings essential nutrients and creates the perfect combination of light and fertilizer for a massive algae bloom. Algae are a big component of marine snow, and Vibrio dutifully colonize the algae at the surface, waiting for them to sink. But the algae and bacteria bloom so quickly, Haddock thinks, they reach a density that triggers glowing before they begin to sink.

"Without a fish to swallow them up, this light may signal the end for these bacteria. Even worse for bacteria hoping to glom onto marine snow and sink, thus making them more attractive to nearby fish, milky seas appear shockingly superficial. The wake of ships parting milky seas are often deep black, suggesting this whole glow occupies only a thin layer right at the top of the water. But if this is the case, could there be a luminous storm of marine snow slowly sinking beneath the surface? Haddock isn’t sure—he suspects the bacteria may die before they sink too deeply—but until scientists can find and travel to a milky sea, no one can be sure."

Comment: Is it part of a Vibrio harveyi lifecycle or just a weird feeding on algae accident? Quarum sensing is beautifully described in the bold. I interpret it as every bacterium releases the signal chemical and if enough individuals are present they sense each other from the concentration level. Our cells sense concentration levels all the time in maintaining our bodies in equilibrium.