Sea off Thailand's Ko Lan turns green in Noctiluca plankton bloom

Heavy rains and floods helped spark a plankton bloom off Ko Lan, a popular tourist island in the northern Gulf of Thailand, turning the sea a bright, pungent green this week. 1 2 Thick patches extended along sections of the coast, with jet skis floating in discoloured water, while other stretches of shoreline were unaffected. 1 Arvut Munhapon, a senior researcher at the Institute of Marine Science, Burapha University, said the colour comes from a plankton called Noctiluca. His team of four was collecting water samples and measuring water quality to build a database of species. 1

Researchers said plankton blooms are a natural, recurring phenomenon but have worsened worldwide as climate change has warmed seas, and that fertiliser runoff and nutrient-rich wastewater feed rapid plankton growth. 1 Blooms typically last two to three days. Anukul Buranapratheprat, the institute's deputy director, said the mass die-off afterwards consumes oxygen and can create hypoxic conditions, an "aquatic dead zone" too low in oxygen to support marine life. 1 Anukul said, based on his own research, that hypoxia in the inner Gulf of Thailand has become more severe, and his biggest concern was a wide hypoxic zone formed this year that is too low in oxygen for bottom-dwelling marine life. 1 2

This year's monsoons and El Niño may be intensifying both the bloom and the hypoxia, since warmer water holds less dissolved oxygen, but Anukul said more research was needed to confirm the connection. 1 Significant flooding has hit Thailand in recent weeks, including in central provinces and Bangkok, adding to the freshwater reaching the Gulf. 1 Food vendors said customer numbers had thinned since the green water appeared, and some visitors moved to unaffected areas. Latipeya Thantibhapat, a 29-year-old tourist from Chiang Mai, told Reuters she did not go in because she feared a rash. 1