Call number: LD2668 .T4 1957 R84 / Master of Science

Graduation date: 1997

Graduation date: 1992

Intertidal rocky shores represent an extremely stressful physical environment dictated by the rise and fall of the tides. One of the major environmental stresses over this gradient is temperature, especially towards the upper reaches of the shore where species spend long periods out of water exposed to hot, desiccating conditions. As a result, the thermal tolerance of intertidal species is often positively correlated with their vertical distributions, and the physiological and molecular limits that drive such patterns have been the subject of recent research. Understanding these tolerance limits, from small (e.g. vertical distribution) to large (e.g. latitudinal) spatial scales, may provide information to predict species’ success under future climate change scenarios, and thus possible changes in community structure. Given their abundance in the high shore, and well resolved taxonomy and phylogeography, the littorinids Echinolittorina malaccana, E. radiata and E. vidua are excellent models to investigate the relationship between thermal tolerance and spatial distribution patterns. These littorinids are widely distributed on Hong Kong shores and exhibit a distinct and consistent vertical distribution that ranges from temperate to tropical regions along the western Pacific coast. Field surveys in summer and winter at two moderately exposed shores (Stanley and South Bay, Hong Kong) showed that E. malaccana was distributed highest on the shore, followed by E. radiata and E. vidua respectively, and all the three species were found ~ 0.25m lower on the shore in summer than winter. Laboratory experiments, including determination of survival limits (LT50), Arrhenius breakpoint temperature of heart rate (ABT of HR) and activities of metabolic enzymes (MDH and LDH), were used to establish if the physiological attributes of the three species were related to their distribution patterns. The LT50 of E. malaccana were the highest of the three species (56.47oC), followed by E. radiata (55.5oC), and finally the lower shore species E. vidua (53.7oC); while ABT of HR in E. malaccana (48.2oC) was also higher than E. radiata (46.5oC) and E. vidua (46.6oC). The enzyme activities did not show any clear patterns. In terms of seasonal variation, LT50 and ABT of HR of all three Echinolittorina species were higher in summer than winter, which showed the potential for the littorinids to acclimate when environmental conditions become more severe. The present study provided a fundamental understanding of how physiological, temperature tolerance may determine the spatial and temporal distribution patterns of Echinolittorina species at a local scale where strong environmental gradients vary vertically and also between seasons. Information on the tolerance limits of physiological traits such as LT50, heart rates and enzyme functioning may direct further investigations to identify the underlying causes of the survival limits of these species to temperature variation, and whether this tolerance is genetically or environmentally determined, for example through acclimation. Such studies will provide insights into how a species' physiology may limit their present-day distributions at multiple scales from local to biogeographical, but also enable predictions of how species may respond to changing temperature regimes. / published_or_final_version / Biological Sciences / Master / Master of Philosophy

As global climate change accelerates, there is increasing concern about how ecosystems may change as a result of biodiversity loss and species replacement. Marine bivalves are important as commercial food resources, ecosystem-engineers and invasive or fouling species. Understanding how beneficial and harmful bivalve species may respond to the changing environment will be important for marine coastal management. Given the expected speed of climate change, it is unlikely that species will have time to evolve adaptively in time, instead, they will have to tolerate environmental stressors or acclimate and vary their life history traits. Studies were conducted to compare the interspecific differences in thermal tolerance between the non-invasive bivalve Septifer virgatus and the invasive Perna viridis, to see if differential tolerance can explain the invasion success of bioinvaders. The intraspecific thermal tolerance of the invasive P. viridis was also assessed to determine how thermal tolerance may differ among populations. In the second stage of the study, by acclimating both S. virgatus and P. viridis at different temperatures, the interspecific differences in thermal acclimation capacity was tested to assess their susceptibility to climate change. As the two species are ecologically and economically important, understanding how they will respond to climate change is important to help manage fisheries and coastal resources. Results showed that S. virgatus had a higher thermal tolerance than P. viridis in the cold and dry season in Hong Kong, but after acclimation at 27°C, which is the average sea surface temperature in the hot and wet season in Hong Kong, P. viridis had significantly increased its thermal tolerance and was more tolerant than S. virgatus acclimated at the same temperature, showing this species has a high capacity for acclimation. In comparison, S. virgatus showed limited acclimation capacity. The results suggest that to conclusively determine the full potential of a species' thermal tolerance, tests have to be conducted in different seasons to take into account phenotypic plasticity. The broad thermal tolerance range and the highly flexible physiology of P. viridis may represent the hallmark of a successful invasive species, and may provide a model for success in a changing world. As invasive species are generally more stress tolerant and plastic, it is expected that global climate change will facilitate bioinvasion, and efforts to manage this will need to take into account the physiological capacities of these species. / published_or_final_version / Environmental Management / Master / Master of Science in Environmental Management

published_or_final_version / Civil Engineering / Master / Master of Philosophy

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