published_or_final_version / Ecology and Biodiversity / Doctoral / Doctor of Philosophy

Physiological response to environmental change is examined in species of the intertidal limpets, Patella (Prosobranchia) and Siphonaria (Pulmonata). Characteristics of heart beat were determined using impedance pneumography and these are described. Heart rate of P. granularis is related to temperature and body size, and cardiac arrest in this limpet is apparently stress-related. Siphonaria oculus may exhibit a temperature-independent, extreme, and often prolonged bradycardia (<10 beats/min). When measured shortly after aerial exposure, heart rate and oxygen consumption of the above limpet species are closely correlated. The relationships of aerial oxygen consumption with body weight and ambient temperature were determined for the above high shore species of limpet. Both have low aerial rates of oxygen consumption relative to low shore limpet species, and their QlO values decrease with increasing temperature. Diel field recordings of heart rate of S. oculus, taken during summer and winter, suggest absence of temperature acclimation, and this was also shown for oxygen consumption at high aerial temperatures (30°C) in laboratory experiments. Oxygen consumption of P. granularis is partially temperature compensated temperature acclimation). In air, even though S. oculus loses water faster, it shows greater tolerance of water loss and survives longer than P. granularis. Prolonged aerial exposure of S. oculus leads to depression of heart rate and of V02 (down to 18% of the pre-exposure rate), responses interpreted as representing adaptive metabolic rate depression. In P. granularis aerial heart rate remains constant and V02 never falls below IX 38% of pre-exposure rate. This reduction in V02 in air is considered as being stress-related, resulting from impairment of oxygen uptake. In declining oxygen tension S. capensis shows a better capacity for oxyregulation than P. granularis. On exposure to hypoxia, sand-inundation and hyposalinity, S. capensis may show typical bradycardia ( <10 beats/min), suggesting depression of aerobic metabolism, and on return to pre-exposure conditions there is no overshoot of heart rate, suggesting absence of oxygen debt. The effect of hypoxia, sand-inundation and hyposalinity on heart rate of P. granularis is variable; this becomes depressed and is often interspersed with extended cardiac arrest. When conditions are normalized, this species exhibits a clear overshoot of heart rate. The significance of differences in physiological response between patellid and siphonariid limpets is discussed with regard to their habitat segregation, particularly in the upper-shore zone (open rock and tidal pools) and sand-inundated rock substrata, where only siphonariid limpets may be found. While not previously characterized in marine gastropods, metabolic rate depression by Siphonaria, through facilitating isolation and conserving food reserves, is suggested as a key factor determining their distribution in physico-chemically more extreme and variable intertidal habitats.

Mobile, rocky shore species often exhibit distinct but dynamic spatial distribution patterns, such as the occupation of microhabitats and formation of aggregations. These patterns are likely to be influenced by the behavioural patterns of a species, their population dynamics and the consequent benefits of adopting particular patterns at certain times of the year. Using Planaxis sulcatus (Planaxidae) as a model species, this thesis documented spatial and temporal variation in the spatial patterns of this species, and attempted to identify the causes and consequences of these behaviours in the seasonally variable Hong Kong intertidal zone. Activity patterns and snail behaviour during activity influenced the locations and types of spatial patterns formed. Planaxis was active and foraged whilst awash, with activity initiated by the ebbing or rising tides. Activity continued until the rock dried on an ebbing tide, or until snails were submerged by the rising tide. Snails were more active and moved for longer durations in summer than winter. When inactive, Planaxis occupied microhabitats such as cracks and crevices in summer and winter, but in the cooler months snails also formed aggregations on open rock surfaces and around microhabitats such as crevices. The extent of aggregation and number of snails in each aggregation showed strong seasonal variation, being greater in the transition period between summer and winter, and differed between sites, being the greatest at one site at Stanley. Seasonal differences in aggregation patterns may be linked with concurrent variation in Planaxis populations which, as a result of life histories events, had a greater abundance of snails and a larger number of recruits in the summer-winter transition, potentially increasing the chances and likelihood of aggregation formation. Microhabitat occupation in the summer provided physiological benefits to the snails. Compared with snails on open rock surfaces during summer low tides, those in crevices remained cooler and suffered less osmotic stress; while individuals in rock pools experienced lower osmotic but not thermal stress. In summer, aggregated snails suffered higher thermal and osmotic stresses than solitary individuals. The winter aggregations, however, showed little physiological benefits; with aggregations of different sizes having no effect on snail body temperatures, and only weak indications of large aggregations relieving osmotic stress. Winter aggregations, therefore, may be linked to minimizing dislodgement risks due to increased wave action at this time. A computer simulation incorporating seasonal differences in population densities, the likelihood and duration of activity, different topographies and three behavioural “rules” produced spatial patterns similar to those on the shore in terms of aggregation sizes, and the proportions of aggregating and crevice-occupying snails. These variables, therefore, play a role in determining the spatial patterns seen in Planaxis. This simple model did not, however, completely match field observations, suggesting that seasonal and spatial differences in distribution patterns involved more complex processes such as variation in local environmental conditions (temperature, wave action, shore topography) and/or biological factors (population densities, size structures, behavioural variation). Further investigations of these processes may better resolve our understanding of how these patterns form and their potential benefits. / published_or_final_version / Biological Sciences / Doctoral / Doctor of Philosophy

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Copies of author's previously published articles inserted. / Bibliography: p. 377-400. / xiv, 400, [20] p., [5] leaves of plates : ill. (some col.), maps ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Zoology, 1995

Typescript. / Bibliography: leaves 563-582. / xiii, 593 leaves ill. (some col.), map