Resumen del producto

The trophodynamics of the Río de la Plata ecosystem over a long time scale (from 1948 to 2008) weresimulated using a food-web model forced by two environmental factors. The Atlantic Meridional Mode(meridional sea surface temperature anomalies) was used as regional forcing, and the Río de la Plata(RdlP) runoff was applied as local forcing. The entire food web was impacted by the regional forcingon a decadal scale; at the inter-annual scale, this remote factor had partial effects on the base of thefood web. The RdlP runoff impacted primary producers and secondary consumers at the inter-annualscale. The higher effects of the local forcing were temporally coupled with seven of the strongest El Ni˜noevents from 1950 to 2008 (1957–1958, 1965–1966, 1972–1973, 1982–1983, 1986–1987, 1991–1992,1997–1998). In contrast, the lower effects of RdlP runoff on the food web were coupled with six of thestrongest La Ni˜na events since 1950 (1950–1951, 1954–1956, 1964, 1970–1971, 1974–1975, 1988–1989).Total system biomass (trophic web attribute) and a measure of system entropy (holistic indicator) wereused to identify ecosystem degradation. The entropy and total biomass of the RdlP ecosystem showedtwo opposite phases: before and after the early 1970s. During the period 1948–1971, the system showedhigh entropy and low total biomass, indicating high degradation. This cycle was reversed after 1972, andprevailed until the beginning of the 2000s. During this new cycle, the system entropy decreased andit was compensated by an increase in total system biomass. A sustainable entropy gain occurred after2003, suggesting a new period of ecosystem degradation. The findings are discussed in light of temporalchanges in the structural properties of this coastal ecosystem.

Palabras clave: Uruguayan coastal waters; Estuarine ecosystem; Long-term environmental disturbances; Biomass variations; Dynamic food web model

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