
‘Red Ghost’ Algae Swarms China’s Coast, Threatening Marine Life
A massive toxic algal bloom has swarmed China’s southern coastline, choking marine life, disrupting fisheries, and covering beaches in thick layers of jelly-like algae. The outbreak, fueled by warming seas and pollution, has spread across Guangdong, the Guangxi Zhuang Autonomous Region, and Hainan.
According to the South China Sea Forecast and Disaster Mitigation Center under the Ministry of Natural Resources, the bloom is caused by Phaeocystis globosa, a common algal species linked to harmful algal blooms, also known as red tides. Locally called the “red ghost,” these blooms can also turn seawater yellow, green, or brown depending on conditions.
Luo Jun, a representative from the South China Sea Forecast and Disaster Mitigation Center, told local media that P. globosa red tides are currently at their peak. Experts warn that the algae produce hemolytic toxins harmful to human health, while the bloom’s decomposition releases hazardous gases.
The rapid proliferation of the algae is also depleting oxygen levels in seawater, leading to hypoxia that threatens marine life. In addition, dense blooms pose a risk of clogging nuclear power plant facilities — an issue previously observed with jellyfish invasions. Authorities warn against visiting affected coastlines or consuming seafood from impacted areas.
The bloom has drawn attention from local residents, who have shared images of algae-covered coastlines on social media. Shenzhen resident and amateur environmentalist Declan Xu posted on the popular lifestyle app Xiaohongshu that beaches in two nearby national parks were blanketed in yellowish-brown, bubble-like algae.
“These algae are especially noticeable when the sea level ebbs,” Xu, who frequently birdwatches in the area, told Sixth Tone. He added that P. globosa red tides have become increasingly common in the area. “This year is particularly severe,” he said, citing two months of dry, sunny weather and the absence of strong cold air as key factors that may be fueling the outbreak.
Xu also urged the public to stop feeding migratory birds, warning that excess food waste could worsen the already eutrophic seawater. “The influx of large amounts of food scraps into coastal areas will worsen the condition,” he said.
Meanwhile, Luo noted that P. globosa red tides can typically last from one week to several months. “Currently, the area affected by this red tide is showing a decreasing trend,” he said.
More than 180 plankton species worldwide can trigger red tides, with 63 recorded in China. Their occurrence is driven by both natural and human factors. Pollutants such as nitrogen, phosphorus, and heavy metals from industrial wastewater, sewage, agricultural runoff, and aquaculture effluent contribute to eutrophication, creating ideal conditions for blooms.
Environmental factors like warm water temperatures, seawater mixing, and sunlight also play a role. In 2024, China’s coastal waters recorded their highest average temperature on record.
Red tides have become a global phenomenon, impacting marine ecosystems and fisheries. Between 2014 and 2023, China recorded an average of 50 red tide events annually, affecting 5,448 square kilometers per year. Some toxin-producing species can contaminate the food chain, posing serious risks to marine life and human health.
Editor: Apurva.
(Header image: An algae bloom at Shenzhen Bay. Courtesy of Declan Xu)