Abstract
Tropical crabs are abundant and seem to play an important role in mangrove ecosystems. Two crab groups are dominant: sesarmids (Grapsidae) and Uea (Ocypodidae). Australian Uea are poorly known. To understand the significance of crab activity on mangrove communities, the behavioural ecology of Uea found in Darwin Harbour was investigated. The aims were to describe distributional patterns and to identify factors important to these patterns.An observational sampling method, developed for quantifying apparent abundance of Uea, was used at various spatial-e.g. creek, habitat, microhabitat-and temporale. g. year, season, tide-scales. Behaviour of different popUlations was observed. Results were used to develop hypotheses that were tested by examining physiological tolerances, morphology, changes in abundance at experimental treatments and survival in different habitats. Ueajlammula were active in lower forests, at wetter, cooler times. This species avoided buttress roots, often interacted with sesarmids and had inconspicuous behaviour.
Uca elegans inhabited high, flat clearings, and apparent abundance increased during windy, less humid weather, provided the soil was wet. Uea elegans' foraging and social behaviours were correlated with crab density. Uea signata's habitats were more vegetated at higher elevations. Sesarmids inhabited lower forests and were associated with buttress roots.
Shade, but not appearance or physical structure of vegetation, significantly affected crab counts. Uea signata, Ueajlammmuia and sesarmids invaded shaded treatments; Uca elegans avoided them. In enclosures, crabs survived longer in clearings than in forests, and U.flammula survived longer than U. elegans. Uca species differed in physiological tolerances, size-thereby strength-and speed.
Physical factors were important in determining distributional patterns and interspecific competition may be significant. Risk of sesannid predation appeared to vary between Uca species and, because sesarmids generally inhabit forests, may influence Uca spatial distribution. Interactions with other crabs may significantly effect the behavioural ecology of Uca.
| Date of Award | Dec 1999 |
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| Original language | English |
| Supervisor | Keith Mcguinness (Supervisor) |