Environmental and ecological factors associated with stinging jellyfish at a tourism hotspot in the Gulf of Thailand

Abstract

The waters of Thailand are associated with some of the most severe cases of envenomation from jellyfish in Asia, often attributed to the extensive marine recreational tourism industry it supports. The western Gulf of Thailand in particular has been shown to host among the highest abundances of box jellyfish, while also being home to some of the highest marine recreational tourism, such as along the Koh Samui archipelago. Here we utilise aspects of the same tourism industry to develop a deeper understanding of stinging jellyfish population dynamics, by combining citizen science at the island of Koh Tao, with dedicated in-situ surveys and remote sensing data. Our analyses of 170 box jellyfish sightings and 81 blooms of Pelagia sp. across a six-year period revealed a strong seasonal trend, with both groups being most abundant between July and December. Decision tree analysis of the complete observation dataset and multiple environmental variables revealed a combination of precipitation and lunar cycle to be the strongest predictors of the assessed stinging jellyfish at Koh Tao. Furthermore, blooms of Pelagia sp. were associated with extensive medusivory by a large diversity of predators, including reef building corals. These observations add to the growing literature showing that scleractinian corals are readily able to ingest larger prey items, either by solitary or protocooperative feeding strategies. Meanwhile, no consumption of box jellyfish medusae was recorded during the study. These findings may allow for improved tourism management practices while also supporting a wider biogeographic assessment of stinging jellyfish in south-east Asia.