Contrasting effects of two burrowing crabs (Chasmagnathus granulata and Uca uruguayensis) on sediment composition and transport in estuarine environments
F. Botto et O. Iribarne, Contrasting effects of two burrowing crabs (Chasmagnathus granulata and Uca uruguayensis) on sediment composition and transport in estuarine environments, EST COAST S, 51(2), 2000, pp. 141-151
The burrowing crabs Chasmagnathus granulata and Uca uruguayensis are import
ant bioturbators of intertidal flats in SW Atlantic estuaries reworking lar
ge amounts of sediment (C. granulata 2234.6 g m(-2) day(-1), U. uruguayenis
678.9 g m(-2) day(-1)) and influencing sediment quality and bedload transp
ort. Their activities increase substrate penetrability. Organic matter and
water content are higher in crab beds when compared with nearby areas witho
ut crabs. Burrows of U, uruguayensis are closed during high tide while burr
ows of C. granulata are always open effectively trapping clay and silt size
particles rich in organic matter. This trapping of sediment enhances the e
ffect of C. granulata in modifying sediment characteristics. Both species i
mpact sediment erodability but have contrasting effects on sediment bedload
transport. Daily bedload transport was lower inside C. granulata beds than
outside, while it was higher in U. uruguayensis beds when compared with co
ntrol areas. While C. granulata stabilizes the sediment by placing fine and
cohesive sediment on the surface, U. uruguayensis disrupts the sediment by
pelletizing it and making it more easily eroded. The contrasting activitie
s of these two species may produce opposing and significant impacts on the
structure of the benthic community because of their impact on sediment stab
ility. (C) 2000 Academic Press.