Food manipulation and selection in the omnivorous grapsoid crab Neohelice granulata (Decapoda: Varunidae)

Abstract

Neohelice granulata is an omnivorous, semi-terrestrial burrowing crab endemic to southwestern Atlantic saltmarshes that behaves as a herbivore when it inhabits vegetated saltmarsh areas or a deposit feeder on bare mudflats. In order to gain insights into how non-specialized crabs manage to rely on low quality diets, we studied in laboratory i) how they use feeding appendages to manipulate the food items commonly eaten (halophytic plant leaves and sediment), and ii) their ability to sort particles when they act as deposit feeders by analysing the food particle content of sediment and stomach. According to the source of food consumed, different behaviours and mouthparts involved in food processing were observed. Sex differences were found in handling halophytic plant leaves in the herbivore feeding mode. In deposit feeding, a concentration of potentially N-rich items of animal origin was detected in stomach contents. Indirect evidence of food item concentration from sediment was revealed by analysis of the C and N content of sediment and feces. N. granulata seems to be an effective deposit feeder even though it lacks the characteristic mouthparts commonly associated with this type of food source.