The black-ribbed mussel, Septifer virgatus, is a northern species which forms dominant bands in the mid-low levels of exposed rocky shores along the Northwest Pacific coast. S. virgatus is thought to reach its southern distributional limits just south of Hong Kong. In Hong Kong, mass mortalities of S. virgatus were recorded with the onset of the hot and wet season, with mussel cover decreasing at the upper limit of the mussel bed at Shek O from 82 % (~1746 ind m-2) in May to 9 % (~ 38 ind m-2) in August 2012. Elevated temperatures played an important role in driving physiological responses of the mussel, including heart rate, oxygen consumption and mantle water and haemolymph osmotic concentrations. The upper thermal limit in water (36 °C, as indicated by the Arrhenius breakpoint temperature, ABT), was unlikely to be reached by local seawater, but the ABT in air (~ 41 °C) was often lower than rock temperatures on Hong Kong shores, suggesting S. virgatus is living at its thermal limit. When immersed, both heart rates and oxygen consumption increased from 25 – 35 °C and dropped beyond 35 °C; whilst in air, haemolymph and mantle water osmolalities increased with duration (0 vs 6 hrs) and temperature (30 vs 40 °C) and 60 % of individuals died at 40 °C after 6 hours. Mortality of S. virgatus is, therefore, linked to the high temperatures and desiccation stress experienced on the shore, which are likely to impose high energetic costs. To better understand the performance of S. virgatus under natural conditions, and the energetic implications of thermal stress on its survival and fitness and hence potential distribution, a Dynamic Energy Budget (DEB) model was constructed. The model had a high goodness of fit. Mussels were predicted to live 5 years, and their main growth and energy reserves were derived from high assimilation during the hot and wet season when food was most abundant, while another slower growth period and reproduction occurred during the cool and dry season. Energy stored in the reserve during growth periods was likely to be allocated to combat thermal stress during the hot and wet season and reproduction during the cool and dry season. The DEB model was used to investigate the energy allocation strategies of S. virgatus under the most conservative and extreme scenarios associated with climate change as projected by the IPCC. The model predicted that reproductive events throughout the mussels’ life-span would be reduced by 30 – 70 %, despite an increase (18 – 470 %) in number of eggs per event. This reduction in the number of reproductive events might not be able to sustain local populations due to the high annual mortality. Such a decrease in performance and fitness, associated with not being able to reach the energy threshold necessary for somatic maintenance, suggests that S. virgatus may be limited to living lower on the shore, where conditions and duration of exposure are more benign, and ultimately experience a northwards range shift as environmental temperatures increase. / published_or_final_version / Biological Sciences / Master / Master of Philosophy

Background: As modern nations undergo demographical and epidemiological transitions, infectious diseases are replaced by non-communicable and chronic illnesses as the main source of ill-health. In particular, the obesity epidemic is of important public health concern as the prevalence of overweight and obesity continues to increase at an alarming rate globally. The trend in childhood and adolescent obesity is also escalating rapidly as people are gaining excess weight at younger ages, representing a growing threat as obesity is linked to a myriad of detrimental psychosocial and physical health consequences which may persist through adulthood. The fundamental cause of obesity is energy imbalance with energy intake exceeding energy expenditure within the human body. Total daily energy expenditures can vary substantially among individuals due to non-exercise activity thermogenesis (NEAT), which accounts for the energy expended from activities we do in daily living, including spontaneous behaviours such as fidgeting. Cumulatively, trivial activities such as fidgeting may accrue to have a significant impact on total daily energy expenditure. Studies have shown that NEAT levels increase or decrease in response to over- and under-feeding, respectively, to counterbalance changes in energy homeostasis. Therefore, fidgeting and NEAT may be an important component in maintaining weight. Decreased levels of fidgeting and NEAT has been hypothesized to be more common among obese individuals as the body fails to activate NEAT in response to over-eating, leading to weight gain. Understanding the correlates of fidgeting and non-exercise physical activity will be helpful in supplementing the design and implementation of effective strategies against obesity. Objective: To investigate the correlates of fidgeting among Hong Kong adolescents, including the association between fidgeting and weight status. Methods: Post hoc statistical analysis was conducted using secondary data from the Hong Kong Student Obesity Surveillance (HKSOS) Project from 2006-2007, which surveyed 34 678 students across 42 secondary schools in Hong Kong. Multivariate logistic regression analyses yielded crude and adjusted odds ratios for the associations of background characteristics, lifestyle characteristics, and dietary intake on fidgeting. Multinomial logistic regression analyses estimated crude and adjusted odds ratios to evaluate the associations between weight status and fidgeting/non-exercise physical activity. Results: Among the sample of Hong Kong adolescents, subjects who were male, older, born outside of Hong Kong, and had daily consumption of fresh fruits, fresh vegetables, and protein were associated with having lower odds of fidgeting. In contrast, high paternal control, high maternal control, smoking, alcohol consumption, elevated levels of daily screen time, exercise time, non-exercise physical activity time, and increased intake in deep fried/fatty foods, snacks/fizzy drinks, coffee, and tea were all associated with having higher odds of fidgeting. Fidgeting did not appear to have any significant relationships with weight status. However, non-exercise physical activity was associated with increased odds of being both underweight and overweight. Conclusions: The results from this study indicate that there are meaningful associations between fidgeting and various correlates, including background demographic characteristics and modifiable behavioural factors. Further studies are required to gain a better understanding of the correlates of fidgeting and their implications to public health. / published_or_final_version / Public Health / Master / Master of Public Health

published_or_final_version / Zoology / Doctoral / Doctor of Philosophy