First Images of Mysterious ‘Milky Seas’ Captured

Bioluminescent bacteria are likely responsible for this rare luminous event covering thousands of square miles of ocean

Satellite image of milky seas near Java.
Satellite image of the “milky seas” event that occurred near the coast of Java in August 2019. CSU/CIRA and NOAA/NESDIS

After spending decades searching for evidence of a rare marine phenomenon called the “milky seas,” an atmospheric scientist at Colorado State University finally got to see in-person photos of the event, reports Linda Geddes at The Guardian. Milky seas are massive glowing tracts of seawater, which until recently, Steven Miller had studied by relying on a combination of satellite imagery and maritime lore, says a statement. But after Miller and colleagues published a 2021 study in Scientific Reports documenting potential milky seas, including one off the coast of Java in August 2019, he was contacted by a first-hand witness to the event, reports Allison Parshall at Inverse.

“I’d say there’s only a handful of people currently alive who have seen one. They’re just not very common—maybe up to one or two per year globally—and they’re not typically close to shore, so you have to be in the right place at the right time,” Miller tells The Guardian. So it was a big deal when Naomi McKinnon, crewmember of a sailing ship called the Ganesha, reached out to Miller with an account of the very same 2019 event that his team had studied through satellite data. “I never thought at the time that I was witnessing something so rare,” McKinnon tells Inverse.

While at first, the Ganesha’s crew had no clue what they had stumbled upon, they shared their photographs with Miller, who soon confirmed that these were some of the first known images of a milky sea event, reports Radifah Kabir at ABP News. The glow from this particular milky sea spanned 38,000 square miles and appeared to the crew members to emanate from about 32 feet below the surface, reports The Guardian. Miller and his colleagues recently published their findings based on the Ganesha’s rare photographs in the Proceedings of the National Academy of Sciences.

Milky sea images taken by the Ganesha crew.
Photographs taken by the crew of the Ganesha of the “milky seas” phenomenon near Java in 2019. Images on the left were taken with GoPro and smartphone cameras and the image on the right was color-adjusted to mimic human vision. Crew of the Ganesha

While it is still unclear exactly how or why the milky seas formed, evidence from the Ganesha points to a type of bioluminescent bacteria called Vibrio harveyi, reports Inverse. According to ABP News, when the crew pulled up a bucket of seawater, they saw consistently glowing light specks, rather than sparkling or flashing lights, which suggests the effect is due to bacteria rather than protists like those that cause red tides.

Kenneth Nealson, a microbiologist at the University of Southern California who was not involved in this study, tells Inverse that the bacteria might use bioluminescence to attract fish. According to this hypothesis, the fish eat the glowing bacteria, and in the process, provide a suitable home for them in their guts.

But the formation of the milky seas might be more complicated than just bacteria looking for a new place to live. Youri Timsit, an environmental microbiologist at the Mediterranean Institute of Oceanography who was not involved in this research, tells Inverse that the phenomenon likely depends on complicated interactions between marine and atmospheric conditions and the organisms in the ocean.

Miller is hopeful that these lingering questions about milky seas can be answered in the future through a combination of satellite data and targeted in-person exploration, reports The Guardian. “The 2019 Java milky sea appeared to last for at least 45 nights, which suggests these things are not just a shot-in-the-dark, one-night event, which would make it almost impossible to get out to one in time. We’ve found that when these larger ones get set up, they stick around for up to several weeks, if not a couple of months,” Miller tells The Guardian.

The researchers hope that more individuals will be able to experience the magical milky seas for themselves. As McKinnon tells Inverse of the Ganesha’s encounter, “We sat up for a long time during the night basking in the glow, accompanied by a light tropical breeze. It was definitely an experience I never want to forget.”