Climate change scenarios experiments predict a future reduction in small pelagic fish recruitment in the Humboldt Current system

Abstract

The Humboldt Current System (HCS) sustains the world's largest small pelagic fishery. While a cooling of this system has been observed during recent decades, there is debate about the potential impacts of rising atmospheric CO2 concentrations on upwelling dynamics and productivity. Recent studies suggest that under increased atmospheric CO2 scenarios the oceanic stratification may strongly increase and upwelling-favorable winds may remain nearly constant off Peru and increase off Chile. Here we investigate the impact of such climatic conditions on egg and larval dispersal phases, a key stage of small pelagic fish reproduction. We used larval retention rate in a predefined nursery area to provide a proxy for the recruitment level. Numerical experiments are based on hydrodynamics downscaled to the HCS from global simulations forced by pre-industrial (PI), 2 × CO2 and 4 × CO2 scenarios. A biogeochemical model is applied to the PI and 4 × CO2 scenarios to define a time-variable nursery area where larval survival is optimum. We test two distinct values of the oxycline depth that limits larval vertical distribution: One corresponding to the present-day situation and the other corresponding to a shallower oxycline potentially produced by climate change. It appeared that larval retention over the continental shelf increases with enhanced stratification due to regional warming. However, this increase in retention is largely compensated for by a decrease of the nursery area and the shoaling of the oxycline. The underlying dynamics are explained by a combination of stratification effects and mesoscale activity changes. Our results therefore show that future climate change may significantly reduce fish capacity in the HCS with strong ecological, economic and social consequences.

The future of coastal upwelling in the Humboldt current from model projections

“…This marine ecosystem is highly susceptible to changes in upwelling patterns, such as alteration in frequency or magnitude (Aravena et al 2014). Significant potential impacts due to climate change have been projected on the spawning rate of small pelagic fish, such as the Peruvian anchovy Engraulis ringens and the sardine Sardinops sagax (Brochier et al 2013), despite the projected temperatures remaining within accepted ecological ranges (Bertrand et al 2004). Small pelagic species strongly depend on zooplankton availability and the exceptional phytoplankton productivity in coastal upwelling zones .…”

“…In effect, the optimal environmental range for primary productivity in coastal marine ecosystems has been associated with moderate upwelling intensity (Cury and Roy 1989;Bakun et al 2015). Outcomes from a coupled physical-biochemical model by Brochier et al (2013) project decreasing nursery areas for small pelagic fish under extreme climate change in the Humboldt ecosystem.…”

“…A significant concentration of nitrate, associated under climate change also depend on additional factors not commonly considered in model formulations, such as ocean acidification (Bakun et al 2015), ecosystem structure (Rykaczewski and Checkley 2008) or external dynamics associated to environmental factors and predators dynamics (Brochier et al 2013). As Travers et al (2007) suggest, these interactions should be addressed with marine ecosystem models comprising physical-biological integration and two-way interactions for the ecosystems components.…”

Under Pressure: Climate Change, Upwelling, and Eastern Boundary Upwelling Ecosystems

“…In the central California Current EBUS, Palacios et al (2004) estimated that stratification has increased since the 1950s in coastal and offshore areas. However, this change may reflect interdecadal variability (Bograd and Lynn, 2003;Chhak and Di Lorenzo, 2007), and its impacts on the nutrient input and consequent biological productivity have not been assessed except by theoretical modeling (Brochier et al, 2013;Schroeder et al, 2014). In other systems, similar studies are lacking due to the paucity of observational data on water-column temperature.…”

“…Nevertheless, a modeling study by Brochier et al (2013), based on downscaling of an AOGCM (Echevin et al, 2012), found that stratification might increase in the Humboldt Current under global climate change. In conjunction with negligible change in winds, their models showed limited nutrient input into the euphotic zone, which would negatively affect biological productivity.…”