Environmental Stress and Its Implications for Behavioural Plasticity of Foraging in Cellana Grata

This dissertation, "Environmental Stress and Its Implications for Behavioural Plasticity of Foraging in Cellana Grata" by Avis, Ngan, 顏基衛, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Abstract of the thesis entitled ENVIRONMENTAL STRESS AND ITS IMPLICATIONS FOR BEHAVIOURAL PLASTICITY OF FORAGING IN Cellana grata Submitted by Avis Ngan For the degree of Doctor of Philosophy at The University of Hong Kong in September 2006 The limpet, Cellana grata Gould, forages whilst awash over the mid-high rocky shore, becoming inactive in refuge habitats when the tide is out. On-shore observations at Cape d'Aguilar, Hong Kong, showed that activity was coupled with tidal fluctuations, but varied in duration and intensity between season (summer and winter), tidal condition (spring and neap tides), sites and days. Percentage activity was generally greater in winter and on neap tides. Limpets showed reduced movement during summer spring tides when the potential duration of activity was reduced, implying a strategy to maximise rasping and hence ingestion. Individual duration of activity was best predicted by time spent awash but not size or resting height, indicating a labile response that varied between individuals. Smaller scale variations in behavioural patterns suggested that C. grata modified its behavioral strategies in response to site-specific environmental variables, such as rock slope and wave splash. Summer mortality rates were not constant but varied with day and site. The highest rates occurred in mid summer (July), with the smallest and largest size classes being most susceptible. Differences in mortality between sites suggested that factors causing mortality were ameliorated by properties of the site and substrate. Habitat selection by the limpets also changed over the summer with decreased usage of stress susceptible microhabitats (open rock surfaces and cracks) and a lowering of the resting height adopted by the limpets. Mortality was not highest in the hottest habitats, reflecting that thermal stress is a combination of environmental factors. Logistic regression models showed that microhabitat type, total bright sunshine, relative humidity and mean air pressure were positively correlated with mortality, whilst rainfall negatively affected mortality. Mushrooming behaviour (lifting the shell from the rock surface) and mortality were not directly related and were influenced by different environmental factors, suggesting that mushrooming may have additional benefits apart from alleviating extreme thermal and desiccation stress. The behaviour of Cellana grata was best predicted by an energy maximising strategy, as assessed by a deterministic model based on the limpets projected energy budget. The temporal behaviour of C. grata was replicated by a state dependent dynamic model, suggesting the organisation of behaviour is similar to the theoretical optimal trade off between constraints of gut volume, energetic costs and gains, and the risk of mortality. Predictions for size-related changes in strategy were not, however, evident in the observed population. The synthesis of data into such models allowed patterns of behaviour to be examined and predicted patterns based on simple parameters, processes and constraints. DOI: 10.5353/th_b3847853 Subjects: Limpets - Effect of stress on - China - Hong Kong Limpets - Behavior - China - Hong Kong