Tree Climbing and Temporal Niche Shifting: An Anti-Predatory Strategy in the Mangrove Crab Parasesarma plicatum (Latreille, 1803)

Parasesarma plicatum, a common sesarmid crab in mangrove habitats of India, always climbs onto the mangrove vegetation during high tide. We studied whether this temporal niche shifting of the crab is an anti-predatory strategy against potential predators that invade their habitat during high tide. We studied the difference in density of this crab on the forest floor and vegetation during low and high tides in three selected study sites. Ex situ experiments were also conducted using the crab and a predatory fish simulating the habitat. The study confirmed that all the crabs climbed onto the vegetation from the forest floor during high tide and came down to the forest floor during low tide. Regression analysis revealed a positive correlation between water level and the height climbed by crabs on vegetation. Crabs completely migrated from sites which were fully submerged during high tide to nearby areas where mangrove trees and the shrub Acanthus ilicifolius provided them ample refuge above water level. Ex situ experiments showed that though P. plicatum could remain under water and feed in starved conditions, they climbed onto the vegetation above water level so as to seek refuge in the presence of predatory fish, Lutjanus argentimaculatus. Therefore, it is inferred that the tree-climbing character exhibited by P. plicatum is a strategy to escape from predators that invade their habitats during high tide inundation and flooding.