Breaking out of the comfort zone: El Niño-Southern Oscillation as a driver of trophic flows in a benthic consumer of the Humboldt Current ecosystem.

The trophic flow of a species is considered a characteristic trait reflecting its trophic position and function in the ecosystem and its interaction with the environment. However, climate patterns are changing and we ignore how patterns of trophic flow are being affected. In the Humboldt Current ecosystem, arguably one of the most productive marine systems, El Niño-Southern Oscillation is the main source of interannual and longer-term variability. To assess the effect of this variability on trophic flow we built a 16-year series of mass-specific somatic production rate (P/B) of the Peruvian scallop (Argopecten purpuratus), a species belonging to a former tropical fauna that thrived in this cold ecosystem. A strong increase of the P/B ratio of this species was observed during nutrient-poor, warmer water conditions typical of El Niño, owing to the massive recruitment of fast-growing juvenile scallops. Trophic ecology theory predicts that when primary production is nutrient limited, the trophic flow of organisms occupying low trophic levels should be constrained (bottom-up control). For former tropical fauna thriving in cold, productive upwelling coastal zones, a short time of low food conditions but warm waters during El Niño could be sufficient to waken their ancestral biological features and display massive proliferations.