This study examined 24 hour activity patterns of a diurnally refuge seeking palaemonid, Macrobrachium australiense. The results obtained improve our understanding of the mechanistic processes that are likely to underlie observed patterns of anti-predatory refuge usage, and diurnal inactivity, in a wide range of crustaceans. When introduced to a novel environment M. australiense altered their searching behaviours in response to changes in available refugia. These behaviours were consistent with attempts to reduce exposure to predation. They altered in response to variation in stalk density of a vegetated refuge, environmental conditions, and individual body size. When settled in the environment all vegetated refuges were attractive to the test species, though higher stalk densities were preferred. M. australiense demonstrated both an active and a passive strategy of mediating exposure to predation. Like numerous other prawn species they substantially reduced activity during periods of high light. The underlying preferences and behavioural mechanisms displayed by the test animals were consistent with the theory that diurnal inactivity is a form of antipredator behaviour, even in the absence of predators. Upon subsequent exposure to predation, refuge seeking behaviour altered depending on the current activity level of the individual: during periods of low activity there was no significant change in behaviour. The presence of a predator had no significant impact upon the occurrence of periods of high activity. However, during these periods the presence of the predator caused an increase in the time prawns spent within the refuge, and decreased the number of transitions between the refuge and the open area.
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Vol. 29 • No. 2