Monsoon dynamics shape spatiotemporal patterns in green sea turtle nesting on an island-based habitat

Abstract

Sea turtles, as endangered and focal conservation organisms, are important in both marine and terrestrial ecosystems but are threatened with extinction due to climate change and human disturbance. Although studies have revealed combined influences of environmental variables on sea turtle reproduction, little is known about impacts of alternating monsoons on their nesting activities on island-based habitats. In the South China Sea, prevailing monsoon winds shift from southwesterly in summer to northeasterly in winter, with transitional periods in spring and autumn. These seasonal wind patterns subsequently change local environmental conditions. Through daily and monthly intensive surveys, we evaluated spatiotemporal variations in the nesting of green sea turtle Chelonia mydas and predicted conditions that increased their probabilities of successful nesting on Taiping Island. The results revealed that the green sea turtles on the island were nested mainly on north coast and nesting proportion increased monthly as monsoon winds changed. They exhibited tortuous routes, particularly on south coast during the summer, and expressed emergence preferences under specific climatic and circadian conditions. The prediction model revealed bimonthly temporal variations following monsoon alternations, with total distance being consistently an important variable, whereas climatic and circadian variables weakly influenced successful nesting under the prevailing southwesterly summer monsoon. Successful nesting additionally was positively correlated with total distance and atmospheric pressure but negatively correlated with straightness index, humidity, tidal height, and daily high tide. Overall, the nesting activities of green sea turtles exhibit spatiotemporal changes on the island-based habitats, and future management and conservation of nesting beaches should consider coastal conditions that may present challenges in response to monsoon alternations.