We observed the behavior of individual crabs in situ. In each habitat, we collected groups of five adult A. pisonii by hand and determined the sex and carapace width (to the nearest 0.1mm) of each individual. The groups of crabs were made up of the first five individuals that we encountered and could capture and were drawn from all accessible habitat. We then painted the carapace of each crab an identifying color with nail polish to aid in identification and visibility. Following a short period of observation to ensure normal behavior, we released the crabs onto a single tree within 10 m of the collection tree of all individuals (mangrove), onto separate S. alterniflora stalks within 10 m of the area of collection (saltmarsh), or onto the same piling (dock) of the dock where all individuals were captured. Release in the saltmarsh occurred during the rising tide when the crabs had no access to the sediment.

We observed crabs in the mangrove and saltmarsh habitats from the time they lost access to the sediment until the receding tide once again allowed access to the sediment (~6h depending on site and day). In contrast, we observed crabs on docks from three hours before slack high tide until three hours after slack high tide. The total time of observation, in minutes, was recorded. Throughout the observational period we recorded the position of the crab as in sun or shade. We calculated the proportion of time during the observational period that each crab spent in the sun and shade.

To further examine the thermal habitat experienced by the observed crabs, we used a FLIR instruments C2 compact thermal imaging camera to take a thermal image of each visible marked crab every 15 minutes throughout the observational period. The days when crabs were observed took place over a wider range of air temperatures, which was measured on site, in the mangrove and saltmarsh habitats than on docks. Thus, to avoid the confounding factor of relatively cooler air temperatures in these habitats, only thermal pictures taken on days which had an average air temperature greater than 29^oC were examined. We then employed the program FLIR tools to obtain the temperature at the center of the carapace of each crab.

We averaged the recorded body temperature of individual crabs over the course of an observational period. We expected that the solar radiation experienced by crabs over the course of an observational period (~6h depending on site and day) would impact their body temperature. Thus, to examine the impact of solar exposure on crab temperature, we obtained short and long-wave solar radiation from the NCEP North American Regional Reanalysis (NARR). NARR has a resolution of 32km and calculates solar radiation in 3hr intervals. We obtained the solar radiation at the grid point closest to each site and averaged the sum of the short and long-wave solar radiation over the observational period. This number, in W/m² was then multiplied by the number of seconds the crab was observed to spend in the sun to obtain a relative measure of the solar energy experienced over the observational period. This calculated variable will hereafter be referred to as “solar exposure”.

Average crab body temperature was calculated as the average body temperature, obtained from thermal photos, over the course of the observational period.

Proportion of time in sun and water were both calculated as the proportion of minutes that crab was observed in the sun or water during the observational period.

Relative solar exposure was calculated by using NARR to obtain the solar radiation at the grid point closest to each site and averaging the sum of the short and long-wave solar radiation over the observational period. This number, in W/m² was then multiplied by the number of seconds the crab was observed to spend in the sun over the course of the observational period to obtain a relative measure of the solar energy experienced over the observational period.

Locations:
Florida East Coast:
Round Island Park: 27o33'33"N 80o19'53"W
Pepper Park: 27o29'42'N 80o18'12"W
Bear Point: 27o25'48"N 80o17'10"W
North Causeway Park: 27o28'28"N 80o19'12"W
Oslo Road: 27o35'14"N 80o21'55"W
Anastasia State Park: 29o52'40"N 81o16'32"W
Guana-Tolomato-Matanzas NERR: 30o0'49"N 81o20'42"W
Palm Valley/Nocatee Canoe Launch: 30o07'57"N 81o23'08"W
St. Augustine Yacht Club: 29o53'09"N 81o17'08"W