The purpose of this investigation was to quantitatively describe the colour patterns of the fiddler crab Uca capricornis and their ability to change on a socially significant timescale. Five experiments were conducted as part of this investigation, with fieldwork completed in East Point Reserve, Darwin (NT) from Nov. to Jan. in 04/05 and 05/06. The five experiments were:
Quantifying colour patterns on the black carapace of the fiddler crab Uca capricornis- To examine the relationship between colouration, carapace size, and sex. This information was used to construct images illustrating the probable colour patterns of various groups of crabs.
Colour changes associated with moulting - Cages were constructed and stocked with crabs which had been measured and photographed. In total 21 individuals (11 females, 10 males) were photographed through at least one moult.
Colour changes associated with the semilunar cycle - During one semilunar cycle, from one neap tide to the next, digital photographs were taken of 22 crabs (10 males, 12 females) active in the cages at approximately low tide. Photos were examined to observe any colour changes on a day to day basis.
Daily colour changes - Twenty-seven crabs (13 males, 14 females) were observed on the day after spring tide over several semilunar cycles. Digital photos of the crabs were taken before, during and after low tide. These photographs were examined for any changes in colour or pattern.
Rapid colour changes - The ability of the crab to change colour over a 20 minute period was assessed using a portable spectrophotometer.