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Title: Aspects of the ecology, behaviour and physiology of the ghost crab Ocypode saratan (Forskål)
Author: Eshky, Ali Adnan
Awarding Body: University of Glasgow
Current Institution: University of Glasgow
Date of Award: 1985
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Abstract:
The ghost crab, oCypode sara tan (Forskal) is the most conspicuous member of sandy beach communities in the Red Sea. The present studies were on populations occurring in the Jeddah region where the crabs burrow in moderately well sorted, mostly fine to medium grain sands above the tide level. The beaches experience small semi-diurnal tides which influence crab feeding behaviour and the level of mean sea level varies seasonally with higher levels (c. 1m) in winter which modify crab distribution since their zones move further up the shore. The crabs exhibited a clear cut zonation pattern with mature males constructing their burrows furthest from the sea, females occurring lower down the supralittoral shore and juveniles confined to a zone close to the water's edge. Most burrows opened towards the sea. Adult male crabs constructed canplex burrows which in the breeding season had a sand pyramid at the entrance of a spiral burrow section from which there could be an extensive system of side branches. The burrows of female crabs were generally of a shallow U-shape but often with the landward shaft stopping just short of the sand surface. Most juvenile burrows were Y-shaped but again with the landward shaft often stopping just below the surface of the sand. The overall distribution of burrows was usually random but there was evidence of territorial spacing of male burrows in some months during the breeding season. A comparison of ambient temperatures and relative humidities with the conditions within the crab burrows showed that the burrows provided protection from environmental extremes. Even in summer when air temperatures approached 400C, temperatures within burrows remained below 300C and at no time were in-burrow temperatures of less than o 20 C measured. Relative humidity within burrows was always high. vii Crabs were usually active away from their burrows around dawn and dusk and during the night. Various crab activities are discussed, especially feeding behaviour. o. saratan can be a deposit feeder, general herbivorous forager, scavenger or predator. Feeding behaviour is discussed in relation to stomach contents and mouthport morphology. viii o. sara tan avoided extreme environmental conditions by behavioural means but also showed physiological adaptation to its high temperature semiterrestrial environment. Branchial morphology, gill area, and branchial volume were examined in a size range of crabs and terrestrial adaptations demonstrated. The species had fewer gills and less gill area than aquatic crabs and had epibranchial 'lungs'. Cardiac and ventilatory activity were investigated. Heart rate varied with body size such that the smallest crabs had the highest heart rates and experiments at a range of temperatures showed adaptation to high temperature conditions. Ventilatory activity indicated different patterns in air and water with special patterns of scaphognathite activity responsible for ventilating the 'lungs' with air and for filling and flushing the gill chamber with water. Weight specific oxygen consumption was examined under aerial and aquatic conditions. This indicated that the smallest crabs had the highest weight specific oxygen consumption and that the rate of aquatic respiration was lower than that in air. QI0 data and information on blood characteristics again indicated both semiterrestrial adaptation and adaptation to a high temperature environment. This was also supported by data on desiccation which indicated that small crabs were more susceptible to water loss than large ones and that loss was greatest in conditions of low relative humidity.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.374509  DOI: Not available
Keywords: QL Zoology Ecology Human anatomy Oceanography
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