Rising surface temperatures lead to more frequent and longer burrow retreats in males of the fiddler crab, Minuca pugnax

The fiddler crab Minuca pugnax occupies thermally unstable mudflat
habitats along the eastern United States coastline, where it uses
behavioral thermoregulation, including burrow retreats, to manage body
temperature (Tb). We explored the relationship between frequency of burrow
use and environmental conditions, including burrow and surface
temperatures, relative tidal height, and time of day, by twenty male M.
pugnax in breeding areas around Flax Pond, New York, USA. We found a
highly significant positive correlation between burrow use and surface
temperature, with a clear shift to longer times underground above 32°C
degrees. We also experimentally heated live crabs in the laboratory and
allowed them to retreat into cooled artificial burrows while continuously
measuring body temperatures (Tb). Laboratory data on cooling times were
compared to field observations of burrow retreat durations. The median
burrow stay in the field of 2.74 min was enough time for our laboratory
crabs to capture over 70% of the cooling potential of artificial burrows
10 or 15 degrees below Tb. Because crab bodies in burrows experience
exponential declines in Tb due to Newton’s law of cooling, there are
diminishing returns to remaining in a burrow, and many crabs probably
leave before coming to equilibrium. For M. pugnax, burrow retreats reduce
time spent feeding and courting, activities that only occur on the
surface. Current concerns about the impacts of climate change on animals
include whether compensatory mechanisms, like more frequent and longer
burrow retreats, will come at the cost of other behaviors necessary for
survival and reproduction.