PARENT SESSION
Oral Session #57: Aquatic Ecology: Wetlands, Estuaries, Marine. Presiding: T. Klinger.
Wednesday, August 8, 2001. 1:00 PM to 5:15 PM. Hall of Ideas J.
Ecosystem engineering at the intertidal: Interaction crabs - halophytic plant facilitates growth of creeks .
Iribarne, Oscar1, Gutierrez, Jorge1, Botto, Florencia1, Palomo, Gabriela1, Perillo, Gerardo2, 1 2
ABSTRACT- The burrowing crab Chasmagnathus granulata is one of the most abundant macro invertebrates on SW Atlantic salt marshes. They are distributed in the bare sediment flats and in areas with the cordgrass Spartina alterniflora and the halophyte Salicornia ambigua. S. ambigua is the dominant species in the salt marshes of the Bahia Blanca Estuary (Argentina) where they form ring-shaped patches of up to 8 m wide. Observations and experiments show that these patches are the result of their interaction with crabs. New S. ambigua plants settle far from the already expanded patches, and as the plant grows, the sediment underneath increases relative humidity and decrease hardness. Crabs construct burrows in these sites facilitated by the presence of the plant. Once crab burrows are established (up to 1 m deep), their sediment removal affects the plants that start growing eccentrically living the central part with dead material and crab burrows. As the patch becomes larger, it may collapse with a tidal channel, being rapidly eroded. Most tidal channels found in this area showed evidences of growing using this mechanism. These evidences show a chain of interactions between ecosystem engineers that have profound ecological effects. They indirectly affect the intertidal community structure. While arachnids and insects characterize high Salicornia marshes, polychaete, clams and crabs dominate low intertidal soft bottoms. Feeding habitats of migratory shorebirds are also affected.
KEY WORDS: Salicornia marsh, burrowing, creek formation, ecosystem engineering