Do Big-headed Turtles Affect the Community and Ecosystem of Hill Streams?

Freshwater turtles have been found to suppress invasive species or dominant grazer populations, alter macroinvertebrate communities and accelerate carcass decomposition. The ecological roles of Asian freshwater turtles are poorly known because wild populations have been severely depleted. For instance, the critically endangered Big-headed Turtle (Platysternon megacephalum) has been widely poached across its native range. However, several remnant populations persist in Hong Kong, providing a valuable opportunity to study their influences on the ecosystem. In this study, we seized the opportunity to examine the effects of the Bigheaded Turtle on three aspects: prey behaviour, macroinvertebrate communities, and food web structure. First, we exposed a common prey item, Sulcospira hainanensis, of the Big-headed Turtle to four different treated waters, e.g., water carrying the smell of the Big-headed Turtle, in controlled laboratory experiments. We observed that the smell of the turtle triggered the snails to hide under a shelter, which is a common antipredator behaviour in freshwater snails. Second, by sampling macroinvertebrates in streams with and without the Big-headed Turtle, we found that the presence of the turtle was associated with a higher abundance of Chironomidae. Third, we aim to construct food webs using stable isotope signatures to demonstrate how the removal of the turtle may affect predator-prey interactions of other members of stream communities. Findings from this study emphasize how freshwater turtles affect the ecosystem at multiple ecological levels, and fill knowledge gaps in our understanding of Asian turtle ecology. Better protection of the Big-headed Turtle and other chelonian species against poaching and other threats do not only conserve these rare animals, but also reduce disruptions to the function and stability of stream ecosystem.