Coupling mechanisms related to benthic production in the SW Gulf of Mexico  <B>Coupling mechanisms related to benthic production in the SW Gulf of Mexico</B><P><B>Luis A. Soto & Elva Escobar-Briones</B><I><P> Benthic Ecology Laboratory, AP 70-305 UNAM, ICMyL, Mexico DF 04510, Mexico</I><B><P> Abstract</B><BR> A long-term study (1983-1988) of the structure and function of the soft-bottom benthic compartment of the continental shelf in the SW Gulf of Mexico, reveals a significant variability in space and time. This system is highly influenced by climatic conditions and the prevailing hydrographic regime; both factors contribute to establish a dynamic system best reflected by two contrasting environmental conditions: stratified versus homogeneous. Intrusion of oceanic water onto the inner shelf, and high river-runoff create a two-layer system which prevents resuspension of organic materials; whereas winter storms create a vertically mixed water column which promotes coupling between pelagic and benthic compartments. Despite the ample seasonal fluctuations observed, total benthic biomass (0.31 g C.m2.y1) exhibited an increasing trend during rainfall and winter storms, attributed to large riverine input prior to the onset of homogeneous conditions on the shelf. Small-scale variability, due to either hydrological or sedimentological factors, is accountable for the biomass fluctuations observed. Benthic biomass on the continental shelf maintained an inverse relation with depth, particularly the infauna (r = 0.85), which displayed an eastwardly increasing gradient from silty to carbonate environments. Coupling between pelagic and benthic compartments was further tested by stable isotopic analysis. The inner-shelf food web mostly received estuarine input, while that of the middle and outer shelf depended on marine carbon sources. Possible energy pathways are proposed in a theoretical trophic model in which production values (g C.m2) were estimated for pelagic and benthic components of the shelf ecosystem.<I><P> Keywords</I>: benthic production, coupling, continental shelf.<P>