PARENT SESSION
Poster Session #25: Marine Ecology.
Wednesday, August 8, 2001. Presentation from 10:30 AM to 12:00 PM. Exhibition Hall
120
The ecological importance of passive deposition of organic matter into burrows of crabs.
Botto, Florencia1, Iribarne, Oscar1, Gutierrez, Jorge1, Palomo, Gabriela1, Gagliardini, Antonio2, Bava, Jose2, 1 2
ABSTRACT- The burrowing crab Chasmagnathus granulata is one of the most abundant macroinvertebrates in saltmarshes of the southwestern Atlantic (southern Brazil to central Argentina). This crab is a deposit feeder that excavates and maintains large funnel-shaped burrows. Bedload and nearbed detritus transport in tidal saltmarshes is one of the pathways to transport marsh-derived organic matter toward adjacent water systems. Mimics of burrows with different width depth ratios and straight tubes were placed in the intertidal to evaluate the efficiency of different burrow shapes in this trapping. After a tidal cycle, the material trapped showed that burrow shapes did not influence the trapping of material when current velocities were high. However, when burrows of different shapes were compared in low current velocities, the most common burrow shapes at field (width-depth ratio = 1) were the ones with higher capture of detritus in the form of small pieces of estuarine plants, and therefore with high percentage of organic matter. However, the straight tubes captured more proportion of sediment that resulted in a higher weight and detritus. Satellite images show that burrows are distributed in the upper part of estuaries and saltmarshes, mostly in areas of low energy covering extensive areas between the marsh vegetation and the open estuary. All evidences suggest that these extensive burrow beds may also be considered a large macrodetritus retention area, reducing the amount of organic matter exported or imported from marshes.
KEY WORDS: Chasmagnathus granulata, organic matter, burrowing