CONICET | Buscador de Institutos y Recursos Humanos

Large parts of the SW Atlantic soft bottom intertidals are inhabited by the burrowing crab N. granulata and the mud crab C. angulatus but they rarely coexist in the same microhabitat. N. granulata, excavates and maintains burrows, generating burrowing assemblages, while C. angulatus is mainly a subtidal species. The increase in habitat complexity generated by theburrows in these large muddy flats and the possible protection from predation by the adults, suggest that burrows may enhance settlement not only for conespecific settlers but also for C. angulatus. The objective of this work was to determine if 1) N. granulata burrows facilitate C. angulatus settlement, 2) there is a stage conditioned predation by N. granulata on C.angulatus, and 3) this influences C. angulatus migration to the subtidal. Burrows were sampled during two summers (2004-2005, 2005-2006), and it was observed that both species settles inside burrows. To evaluate the mortality of recruits inside burrows, we performed a field experiment with juvenile and adult crab exclusion cages that only allows first instars of crabs topass through the mesh and inclusion of juveniles or adult of N. granulata. The results showed differences in crab sizes between treatments, due to predatory interactions that depended on size. When only juveniles of N. granulata were present, the higher mortality of C. angulatus was observed in smaller crabs. However when adults of N. granulata were present, larger juvenilecrabs suffered the highest mortality. These results suggest that adults are preying upon larger juveniles reducing the mortality of the smaller ones that are preyed by the larger ones. We also measured emigration from these burrowing assemblages using bi-directional pitfall traps, which shows that 20 % of C. angulatus juveniles are leaving the burrows towards the subtidal. Herewe demonstrated that N. granulata have important effects on the settlement of C. angulatus.

enviar mensaje