Date of Award


Degree Type


Degree Name

Master of Philosophy (MPHIL)


Environmental Science


Freshwater turtles and tortoises are ecologically important organisms; however, they are underappreciated, and conservation attention often focuses on the more charismatic animals such as birds and mammals. Although turtles are the most traded group of animals and many species are at the brink of extinction, little research has been done to understand their ecology in Asia because of the rarity of wild populations. Hong Kong is a biodiversity hotspot for freshwater turtle species. The Big-headed Turtle (Platysternon megacephalum) is a critically endangered species that still maintains small populations in Hong Kong, providing a rare opportunity to study the ecological impacts of freshwater turtles on the community and ecosystem in hill streams.

I study the ecological impacts of P. megacephalum in two parts. First, I carried out a laboratory experiment to study the anti-predatory behaviour of freshwater snails (Sulcospira hainanensis), which dominate the diet of P. megacephalum. Second, I did field experiments to examine the macroinvertebrate community, the primary production and decomposition rates in streams with and without P. megacephalum. Overall, I aim to gain a better understanding of the effect of P. megacephalum on population, community and ecosystem. I hope that the results will highlight the ecological importance of Asian freshwater turtles, initiate further studies of the species and support Asian turtle conservation.

In Chapter 1, I present a literature review summarising the threats against wild turtle populations and the ecosystem. I also provide our current understanding of the ecology of the study turtle species, P. megacephalum. In Chapter 2, I describe and present the behavioural study of snail anti-predatory behaviour against different predatory risks. I found that the smell of turtles triggered snails to hide under shelters, and this behaviour was stronger with adult turtles compared to juveniles. I also found that snails moved less and become more alert as time passed. In Chapter 3, I compare the macroinvertebrate assemblage and ecological processes in turtle-present and turtle-absent streams in Hong Kong. I found that the presence of turtles increased the chironomid larvae abundance, but has no effect on the abundance and diversity of other macroinvertebrates. Additionally, primary production and decomposition rates changed with certain macroinvertebrate abundance, but not with turtles. In Chapter 4, I summarise the major findings of each chapter, then discuss the importance of ecological studies of turtles. Understanding the ecological importance and having the opportunity to appreciate wildlife in the wild are sometimes the gateway towards successful conservation. I hope that my work can highlight the importance of P. megacephalum and support local conservation of the species.



Recommended Citation

Fok, W. L. (2023). The effects of the Big-headed Turtle (Platysternon megacephalum) on community and ecosystem in Hong Kong hill streams (Master's thesis, Lingnan University, Hong Kong). Retrieved from