MEPS 312:201-210 (2006)  -  doi:10.3354/meps312201

Ecological importance of passive deposition of organic matter into burrows of the SW Atlantic crab Chasmagnathus granulatus

Florencia Botto1,2,*, Oscar Iribarne1,2, Jorge Gutierrez1,2, José Bava2,3, Antonio Gagliardini2,3, Ivan Valiela4

1Departamento de Biología (FCEyN), Universidad Nacional de Mar del Plata, CC 573 Correo Central, 7600 Mar del Plata, Argentina
2Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Rivadavia 1917, 1033 Buenos Aires, Argentina
3Instituto de Astronomía y Física del Espacio, CC 67, sucursal 28, 1428 Buenos Aires, Argentina
4Boston University Marine Program, Marine Biological Laboratory, 7 MBL Street, Woods Hole, 02543 Massachusetts, USA

ABSTRACT: The burrowing crab Chasmagnathus granulatus is the most abundant bioturbator in estuarine intertidal sediments from southern Brazil to central Argentina. This crab is a deposit feeder that excavates and maintains large semi-permanent open burrows with funnel shaped entrances. In this study we showed that the funnel shaped burrows with low aspect ratio are the most common and, with field experiments, we demonstrated that these burrows are also the most efficient in the capture of organic matter. As shown by C isotopic signatures, the origin of trapped detrital material is Spartina densiflora. Burrows are distributed in the upper part of estuaries and saltmarshes, mostly in areas of low energy, and cover extensive areas between the marsh vegetation and the open estuary. Through sampling of crab densities and use of satellite images, we estimated the number of burrows of different shapes in the Bahia Blanca estuary (38°50’S), one of the largest estuarine intertidals in the SW Atlantic. After combining this information with the trapping efficiency of burrows of different shapes, we estimated that within 100 d, a crab bed could capture the entire annual production from a marsh area of similar size. Therefore, we suggest that these extensive burrow beds may be considered large macrodetritus retention areas, reducing the amount of organic matter exported from marshes but locally increasing the sediment organic matter content.

KEY WORDS: Spartina-marsh · Chasmagnathus granulatus · Burrowing · Detritus dynamics

Full text in pdf format