A strange single-celled organism that acts both as a plant and an animal has come to dominate wintertime algal blooms in the northern Arabian Sea.Winter blooms of Noctiluca scintillans, also known as the sea sparkle, have displaced microscopic algae called diatoms that form the basis of the marine food chain, a paper in Nature says.Scientists at Columbia University fear the outbreaks could herald massive declines in fisheries in the region, potentially impacting millions of fishers in India, Pakistan, Iran, Oman and Yemen.They have linked the emergence of N. scintillans blooms with the loss of ice cover in the Himalayan-Tibetan Plateau driven by climate change. Satellite imagery of 2014 Noctiluca bloom off the coasts of Iran and Pakistan. Image courtesy of Joaquim I. Goes. Surface bloom of Noctiluca in the Arabian Sea in 2009. Image courtesy of Joaquim I. Goes. Noctiluca cells in seawater collected in a beaker. Image courtesy of Joaquim I. Goes. Cells of Noctiluca, a unicellular organism, visible in a beaker. Image courtesy of Joaquim I. Goes. A green Noctiluca cell with endosymbionts visible under a microscope. Image courtesy of Joaquim I. Goes. On Feb. 26, 2003, a group of scientists set out to sea from Goa, India, on a routine mission. They called it “sea truthing,” verifying data gathered by satellites eyeing the earth from hundreds of kilometers above. What the team encountered there, in the middle of the Arabian Sea, was far from routine. About 970 kilometers (600 miles) northwest of Mumbai on India’s western coast, they found themselves sailing on a green swirl that spread out as far as the eye could see. At night, the waters glowed neon blue. The light was emitted by millions upon millions of a strange single-celled organism: Noctiluca scintillans, or the sea sparkle. It had never been found in these waters in such abundance before. Despite its luminescence, the N. scintillans blooms are a harbinger of darker tidings, a paper published in Nature earlier this year warns. A map produced using satellite data on chlorophyll concentration. The red swirls indicate the presence of Noctiluca blooms in the Arabian Sea in February 2009. Image courtesy of Joaquim I. Goes. The outbreaks occur every winter in the northern Arabian Sea, stretching from India’s western coast to the edges of the boot-shaped Arabian Peninsula. Scientists at Columbia University say they fear the rise of these blooms could herald massive declines in fisheries in the region. “We are seeing an ecosystem shift in the Arabian Sea,” said Helga do Rosario Gomes, one of the study’s authors. “That can cause massive declines in fisheries and ultimately lead to the emergence of a dead zone.” If the team is right, it would jeopardize the livelihoods of more than million fishers living in settlements sprinkled along the coasts of India, Pakistan, Iran, Oman and Yemen. A plant and an animal Noctiluca cells in seawater collected in a beaker. Image courtesy of Joaquim I. Goes. Gomes and her husband, Joaquim I. Goes, run a lab at Columbia University’s Lamont Doherty Earth Observatory in New York. For almost two decades, the couple has studied the sea sparkle blooms that have baffled scientists on at least three continents. N. scintillans is a dinoflagellate: it has two strands of antennae-like flagella projecting from its cell membrane. They guide food to its mouth and help it to move. But when researchers first examined the cells closely in 2003, it was not the flagella that caught their attention. Gomes remembered being struck by what was inside the N. scintillans cell. Within its translucent globular structure were other cells, tiny verdant ones. These endosymbionts living in the N. scintillans cell were the reason for its atypical green color. Usually, the microorganism is red in color.