Grooming and agonistic behaviors in the semi-terrestrial crabs Ocypode quadrata (Fabricius, 1787) and Minuca (Uca) burgersi (Holthuis, 1967) (Decapoda: Brachyura: Ocypodidae)

Abstract

Grooming behaviors reduce body fouling and are well documented in crustaceans. There are more detailed laboratory-based grooming studies on fully aquatic crabs compared to semi-terrestrial crabs. By contrast, semi-terrestrial crabs are predicted to have different grooming time budgets than fully aquatic crabs because semi-terrestrial crabs are not constantly submerged in water that can mechanically remove sedimentary fouling, whereas fully aquatic crustaceans have increased fouling from algae and epibionts. We studied the grooming behaviors of two semi-terrestrial crab species. Crabs (N = 50 ghost crabs, Ocypode quadrata (Fabricius, 1787); N = 50 fiddler crabs, Minuca (Uca) burgersi (Holthuis, 1967)) were observed in isolation for 45-min trials. We recorded grooming frequency, location, appendage, and time. Ghost crabs were also observed in agonistic encounters to determine how grooming varied in the presence of a conspecific individual. Ghost crabs and fiddler crabs have different grooming time budgets, (0.526 and 0.895%, respectively) with both species having lower grooming time budgets than fully aquatic crustaceans. Some similarities and differences in grooming between the two semi-terrestrial crabs exist, with both species frequently grooming their eyes and maxillipeds using a brush or scrape mechanism, but with fiddler crabs using their eyes as a grooming appendage more frequently than ghost crabs. Ghost crab males groom less than females, whereas fiddler crab males and females groom equally. In agonistic interactions in ghost crabs, the grooming time budget decreased compared with isolated observations and individuals engaged in a “playing dead” behavior (thanatosis) after engaging in a fight. Semi-terrestrial crabs were found to groom significantly less than fully aquatic crustaceans.