IIMYC   23581
INSTITUTO DE INVESTIGACIONES MARINAS Y COSTERAS
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Food manipulation and selection in the omnivorous crab Neohelice granulata.
Autor/es:
LANCIA, JUAN; BAS CLAUDIA; SPIVAK, EDUARDO
Lugar:
Frankfurt
Reunión:
Congreso; 8th International Crustacean Congress (ICC-8); 2014
Resumen:
Neohelice granulata (Decapoda, Varunidae) is an omnivorous semi-terrestrial burrowing crab endemic of Southwestern Atlantic saltmarshes that behave as herbivore when inhabit vegetated saltmarsh areas or deposit feeder in bare mudflats. In order to elucidate how non-specialized crabs manage to rely on low quality diets, we studied how they use feeding appendages to manipulate the different food items commonly eaten, and evaluated their ability to sort particles when they act as deposit feeders. According to the source of food consumed, different behaviors and mouthparts involved in food processing were observed. Differences were found in handling Spartina densiflora leaves in the herbivore feeding mode among crabs of different sex and size. Females and younger males separated the longitudinal fibers of a leaf with their chelae and cut a thin strand with their mandibles. Large males used their chelae to bend the entire leaf before cutting it along the fold with their mandibles, handling the resulting piece with both chelae. The subsequent phase of fractioning and ingestion was similar in both sexes: dactylus of 3rd maxilliped holds and guides cut pieces into the mouth, food was manipulated by the dactyl of 2nd maxilliped and processed by mandibles; finally the small sectioned pieces were ingested. When feeding on sediment, no differences were observed between sexes. Each individual roamed through the area introducing occasionally their chelae into the sediment and carrying some mud into the mouth. During this raking, sometimes crabs found larger items (mainly plant detritus) taking them between propodus and dactylus before carrying to the mouth. Otherwise, they eventually stopped in a given area and ingest sediments with one or both chelae alternately as spoons. Third maxillipeds were not used in sediment manipulation and remained open. In contrast, dactyls of 2nd maxillipeds actively pushed the sediment obtained by chelae into the mouth or helped to expel undesirable portions. Activity of maxillules, maxilles and first maxillipeds was not evident during feeding on sediment. In deposit feeding, a concentration of N-rich items in stomach contents was detected. Diatoms and nematodes concentration was lower in stomach than in sediment; ostracods, copepods and foraminifera were more abundant in stomach content; S. densiflora remains did not differ between sediment and stomachs. C and N content in feces was higher than in sediment. Neohelice granulata is found in all areas where some species of Spartina are present. The ability of this crab to degrade cellulose and feed on vascular plants is presumably associated to their success in colonizing Southwestern Atlantic marsh environments. However, it is also able to select energy rich items from sediment, compensating the limited periods of feeding after each tidal receding allowing them to obtain the necessary complement to an N-low diet. In spite of lacking the main morphological characteristics associated to feeding on sediment, as small spooned chelae or profuse and diverse setation in feeding appendices and/or body surface, N granulata could be an effective deposit feeder.