The harbor in Hong Kong sparkled with an eerie blue glow, painting a surprising and beautiful picture. But few people know that the cause of this lovely landscape is actually pollution – pig manure, fertiliser and sewage. This nutrient-rich pollution encouraged a bloom of Noctiluca scintillans, commonly known as “Sea Sparkle.”

Long exposure image of bioluminescence of N. scintillans in the yacht port of Zeebrugge, Belgium. Photo by Hans Hillewaert

They may look like algae, but Noctiluca scintillans is actually plankton. Unable to photosynthesize, they feed on algae in many marine environments across the world. This phytoplankton is not considered dangerous and is fairly common in and around Hong Kong. When the water is still, you couldn’t even tell that it’s there, but when the water is disturbed, it starts to emit this blue light. Local photographer Lit Wai Kwong took some lovely pictures:

“You can see the blue light if there is a wave, a boat moving, or a stone thrown in the water,” said Kwong, who used a 30-second exposure to get the shot. There was no blue light when the water was calm, therefore many people threw stones into the water in order to see it.”

But despite its beauty, this bloom indicates a significant danger. While the plankton is not toxic in itself, it blooms when there is significant runoff in the water. So it’s a sign that there is great pollution in the area.

“The plankton and Noctiluca become more abundant when nitrogen and phosphorous from farm run-off increase,” Borenstein wrote, “Noctiluca’srole as both prey and predator can eventually magnify the accumulation of algae toxins in the food chain.”

Indeed, Noctiluca can also deplete the oxygen of water, causing significant environmental damage and potentially wiping out the water’s other inhabitants. In the Arabian Sea there is an area about the size of Texas blooming with this plankton, and not much else can live in those waters. If water pollution continues, the same might happen in Hong Kong.

“Hong Kong and the entire Pearl River Delta has a big problem with wastewater, and that is surely a factor with these plankton blooms,” said David Baker from the Swire Institute of Marine Science at the University of Hong Kong.  “I guess the analogy is they’re like locusts that feed on agricultural crops. And once they find a good abundant food source they will multiply until the food source is exhausted. In Hong Kong unfortunately most of the nutrients are coming from our own sewage.”

The bloom’s end is actually the most dangerous part. As the tiny organisms perish, they sink to the bottom of the sea, decomposing and consuming huge quantities of oxygen.

“That’s when we have the formation of these dead zones, where anything that’s living, any fish or crab species living on the bottom, is at risk of dying from the low oxygen associated with that decomposition,” Baker said.

After something happens, it’s very difficult for the wildlife to bounce back.