Meeting Abstract
Different demographic groups within a population (i.e., males/females, small/large individuals) are often distributed differently along environmental gradients, suggesting different ecological or physiological needs. The intertidal zone porcelain crab Petrolisthes cinctipes is distributed along a vertical thermal gradient within the intertidal, though it is currently unknown how individuals are distributed along this gradient. We monitored under-rock temperature and crab demographics (size, sex) over summer and autumn months in fixed transects along the species’ vertical distribution boundaries. In the upper intertidal, under-rock temperatures were strongly size dependent, with smaller rocks reaching temperatures up to 37°C but larger rocks never exceeding 20°C. Lower in the intertidal, rock size was less important and no rocks exceeded 17°C. Results show mean crab density much lower in the warm high intertidal (83 crabs/m2) compared to the cooler low intertidal (171 crabs/m2). In addition, we found male-skewed sex ratios in the upper and lower intertidal zones where male crabs were 25% and 21% more abundant than female crabs respectively. From these data we can conclude that under-rock temperatures influence demographic parameters of P. cinctipes within the intertidal.
