Sediment dynamics modulated by burrowing crab activities in contrasting SW Atlantic intertidal habitats.

ESCAPA, C.M.,; PERILLO G.M.E.; IRIBARNE, O.O.,

ESTUARINE COASTAL AND SHELF SCIENCE

Elsevier

Lugar: Amsterdam; Año: 2008 vol. 80 p. 365 - 373

0272-7714

Biogenic bottom features, animal burrows and biological activities interact with the hydrodynamics ofthe sediment–water interface to produce altered patterns of sediment erosion, transport and depositionwhich have consequences for large-scale geomorphologic features. It has been suggested that dependingon the hydrodynamic status of the habitat, the biological activity on the bottom may have a variety ofeffects. In some cases, different bioturbation activities by the same organism can result in differentconsequences. The burrowing crab Neohelice granulata is the most important bioturbator at SW Atlanticsaltmarshes and tidal plains. Because of the great variety of habitats that this species may inhabit, it ispossible to compare its bioturbation effects between zones dominated by different hydrodynamicconditions. Internal marsh microhabitats, tidal creeks bottoms and basins, and open mudflats wereselected as contrasting zones for the comparison on a large saltmarsh at Bahı´a Blanca Estuary (Argentina).Crab burrows act as passive traps of sediment in all zones, because their entrances remain openduring inundation periods at high tide. Mounds are generated when crabs remove sediments from theburrows to the surface and become distinctive features in all the zones. Two different mechanisms ofsediment transport utilizing mounds as sediment sources were registered. In the first one, parts of freshmound sediments were transported when exposed to water flow during flooding and ebbing tide, withhigher mound erosion where currents were higher as compared to internal marsh habitats and openmudflats. In the second mechanism, mounds exposed to atmospheric influence during low tide becamedesiccated and cracked forming ellipsoidal blocks, which were then transported by currents in zones ofintense water flow in the saltmarsh edge. Sedimentary dynamics varied between zones; crabs werepromoting trapping of sediments in the internal saltmarsh (380 g m2 day1) and open mudflats(1.2 kg m2 day1), but were enhancing sediment removal in the saltmarsh edge (between 10 and500 g m2 day1 in summer). The implication is that biologically mediated sedimentological changescould be different among microhabitats, potentially leading to contrasting geomorphologic effects withina particular ecosystem.