The emergence of ghost crabs from their burrows seemed to be keyed more to 
temperature than to season. Figure 16 plots the number of ghost crabs found 
against temperature. It is obvious from this figure that ghost crab activity 
is triggered when temperatures reach about 15° Celsius. Landy (1977), using 
controlled temperature chambers, has established that the critical temperature 
is 16° Celsius. The fact that temperature serves as the activity trigger rather 
than day length or some other seasonal factor is borne out by the fact that 
ghost crabs were found on a particularly warm night in early December 1977 after 
several weeks of inactivity (Fig. 15). 
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Air Temperature (°C ) 
Figure 16. Ghost crab (Ocypode quadrata) densities at Fort Macon as they 
correspond with air temperature. Points are represented by small 
circles. No activity was recorded at temperatures below 15° Celsius. 
At 15° Celsius burrow activity was evident (noted by a star) but no 
crabs were seen. The study was repeated three times, and the 
points in the center of slashed vertical lines represent the mean 
number of crabs. The lines represent the range. 
Density of ghost crabs was depressed following nourishment. The postnour- 
ishment summer population peak was nearly 50 percent lower and came nearly a 
month later than the peak the summer before nourishment (Fig. 15). This would 
seem to be a significantly greater difference than can be explained by the 
simple yearly variation. The mechanism responsible for the decrease is not 
clear, but one of the following seems likely: 
(1) The ghost crabs could have been buried in their burrows during 
their winter dormancy period. 
29 
