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

Abstract

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 (), 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.

The Early Life History Transitions of the Bivalve Aulacomya atra From the Humboldt Current System Off Peru Are Affected by Human Exploitation and Modulated by El Niño–La Niña Cycle

“…Seasonal changes in the frequency and magnitude of upwelling pulses -with the concurrent changes in temperature and food availability -have been suggested to drive the chronology of the reproductive cycle of A. atra at several locations in Chile (Jaramillo and Navarro, 1995;Cantillánez, 2013, 2014). In our case, strong decreases in the SSB, which most likely reflect spawning episodes (Riascos et al, 2017), coincide with periods of drops in the SST in Bahía Independencia (e.g., Vélez et al, 2005). This suggests that the reductions in the SSB, reflecting periods of gamete release, are influenced by seasonal pulses of cold water.…”

“…A more plausible explanation for the increased recruitment during EN, despite a simultaneous drop in the SSB, seems to be a reduction in interspecific competitive interactions during the recruitment phase of A. atra on shallow benthic areas from Bahía Independencia that may overcompensate for the mortality associated with abiotic stress. This mechanism was described by Riascos et al (2017) to explain the increased recruitment of the scallop A. purpuratus during EN in 1997-1998 in this bay; there was a decreased competition for food with filter-feeder polychaetes and a decreased predation by crabs, which were negatively affected during EN (Taylor, 2008).…”

“…Therefore, it is possible to have densities for each month (Gayanilo et al, 2005). Previously, the growth parameters (L∞, K) were calculated using the routine ELEFAN_SA in TropFishR (see Riascos et al, 2017) and the estimate of "t0" was obtained by the Pauly equation (Pauly, 1983):…”

“…factors, through teleconnections (Riascos et al, 2017). Therefore, we included variables describing environmental variability at macro, regional, and local spatial scales.…”

The Decreasing Availability of Settlement Surfaces Affects the Transition From Larvae to Early Recruitment of the Scallop Argopecten purpuratus Through El Niño and La Niña Episodes

“…Populations of A. purpuratus typically display outbreaks during exceptionally strong El Niño episodes, resulting from faster recovery between spawning events, increased larval production, increased settlement of larvae and increased survival rate and somatic production of juveniles (Illanes et al, 1985;Wolff, 1987;Cantillánez et al, 2005;Wolff et al, 2007). These changes seemingly herald responses of a relict of tropical Miocene fauna that evolved in the cold Humboldt Current System but retained warm water characteristics because recurrent El Niño episodes (Wolff, 1987;Uribe et al, 2012;Riascos et al, 2017). Therefore, it is surprising that larval abundance of A. purpuratus increased only slightly during El Niño 1997-1998 ( Figure 5A).…”