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.