The smear of “blue tears” on Taiwan's Matsu Islands lures many to its coasts to witness the gleam of bioluminescent plankton. Yet sometimes there is danger in the glow of too much beauty. 

In a first, scientists have now tracked these creatures, called red Noctiluca scintillans (NS), in the East China Sea using satellite imagery. These dazzling “sea sparkles,” as they’re also known, form red tides when waters fill with too many nutrients, growing rapidly into blooms that can be deadly. When they proliferate out of control, they can drain oxygen from the surrounding waters, killing marine life in the process.

"Red NS itself is not toxic (i.e., doesn't produce toxins). However, at high concentrations, they may block sunlight, use up oxygen, or release ammonia to create a hostile environment to marine animals," said co-author Chuanmin Hu, from the College of Marine Science at the University of South Florida, to IFLScience.

To “fingerprint” these critters from above, the team analyzed almost 1,000 images taken by instruments onboard two NASA satellites and the International Space Station from 2000 to 2017. The “fingerprint” is based on their ability to absorb blue light and scatter red light in a unique ratio compared to their ocean peers. 

"More than 10 years ago, researchers already noticed its unique color, but were suspicious whether satellites can capture them because a bloom patch can be too small for satellites," said Hu. "What we found was that even if the size of the bloom patch is only a few [percents] of a satellite pixel, it can still be detected. Because satellite observations can go back several decades, the findings set a template to study their historical changes and to understand what caused such changes."

They found that the range of N. scintillans was previously underestimated, with many blooms located farther from the coast than expected. The results also suggest the creatures can live in waters around 28°C (82°F) – a 2 to 8°C increase on previous estimates. 

However, the blooms appear to be increasing, with 2017 seeing a particularly long bloom that persisted from mid-April to mid-July. It’s possible nutrient runoff from farms contributed to the excessive build-up of nutrients in the water, disrupting the delicate ecosystem and producing toxic red tides. Other possible reasons include higher?than?usual temperatures and increased light availability. The team can’t say for certain whether this trend will continue, but it is cause for further observation. 

The authors suspect the construction of China’s controversial hydroelectric gravity dam called the Three Gorges Dam is the reason there were fewer blooms in the early 2000s. They also suggest the satellite data can be used to improve tourism sightings of the region's “blue tears."

One “significant limitation is that the current detection is only applicable to near?surface high concentrations of red Noctiluca scintillans,” write the authors of the study published in the journal Geophysical Research Letters. However, they may be mixed throughout the water column, making accurate detection difficult.

"There is actually much follow-up work to do, one of which is to keep monitoring the red NS to see whether the recent increasing trend will continue and why. For example, is the change due to human activities or to climate variability?" added Hu. "Increases in red NS around beaches may be a good thing for tourism and tourists, but if their concentration is too high, they can form red tides and be harmful to marine life – a double-sided sword."