Co-ocurrence of two species of crabs with similar ecological traits: dominance, feeding and burrowing behaviour

GABRIELA PALOMO; PAULINA MARTINETTO; MARTIN BRUSCHETTI; OSCAR IRIBARNE

Cairs, Australia

Conferencia; The Society of Wetland Scientists 27th International Conference and the Australian Marine Sciences Association 44th Annual Meeting; 2006

Society of Wetland Scientists y Australian Marine Sciences Association

When two similar species coexist, the strength of intra-specific competition increases. Ecological differences between species allowed them to escape or minimize competition. In this study, we investigated if in the absence of the dominant competitor Cyrtograpsus angulatus takes the habitat and feeding mode of the competitor. We predicted that in absence of the dominant crab species, (1) C. angulatus would construct burrows and feed on the sediment, (2) sediment with a higher density of burrows would have higher water content, organic matter content and silt proportion than sediment without crabs. In areas where both species coexist, we predicted that on exclusion of the dominant crab, C. angulatus would take the ecological role (define here as habitat and feeding mode) of the dominant species. Sampling on a C. angulatus crab bed on Caleta Valdés was performed, analyzing characteristics of crab burrows and sediment with spatial autocorrelograms. Feeding mode of crabs was determined analyzing the stomach content of 160 individuals. Manipulative experiments were performed in Mar Chiquita coastal lagoon to distinguish between the effect of Ch. granulata, C. angulatus or both species on sediment physico-chemical characteristics. Our results showed that the C. angulatus inhabit dense crab beds in Caleta Valdés. The density of burrows was correlated with the sediment silt proportion and the organic matter content. The crabs were mainly deposit feeders. Results from the experiments suggest that crabs decreased the water content, organic matter content and the silt proportion of the sediment. These effects occurred only in the mud area. This study supported the model that in the absence of the dominant competitor, Cyrtograpsus angulatus would change its feeding mode and the habitat. Interactions such as competence are strongest among species with similar functions and this enhances the functional diversity of a system making the habitat less vulnerable to disturbance.