Spatial and interannual variability in the distribution of euphausiid life stages in the permanent upwelling system off northern Chile

Abstract

Euphausiids are crustaceans with a complex life cycle that play a significant role in the trophic pathways of the highly productive Humboldt Upwelling System. We studied the effect of upwelling and climate variability on the austral spring distribution and abundance of krill life stages using 8 years of physical and biological sampling off northern Chile. During the study period, conditions shifted from negative to positive temperature anomalies and climate indices. Consequently, large interannual variability associated with the El Niño Southern Oscillation and the Pacific Decadal Oscillation was observed in all life stages, with lower abundances during their positive phases. The distribution patterns and the statistical associations with environmental variables show that the effect of upwelling varies ontogenetically. Eggs, nauplii, calyptopis, and furcilia larvae had higher abundances offshore, suggesting they are transported offshore through the Ekman layer. Juveniles and adults avoid advection via their deeper distribution and vertical migrations, and although they were present in the entire study area, abundances were higher to the south associated with lower salinity. This is the first study evaluating the impacts of climate variability on krill life stages and finds a direct effect of these low-frequency oscillations on krill reproduction and abundance in the HUS.

Disentangling species-specific krill responses to local oceanography and predator’s biomass: The case of the Humboldt krill and the Peruvian anchovy

“…Krill communities of the HCS are strongly influenced by the hydrographic structure and advective processes associated with upwelling dynamics. The cross-shore distribution of krill life stages in northern Chile suggests that, during spring months, early stages are advected offshore through the Ekman layer (Dıáz-Astudillo et al, 2022). Similar observations have been made in central Chile, where upwelling is highly seasonal, and smaller individuals are usually found farther offshore (Riquelme-Bugueño et al, 2012).…”

“…The region presented high environmental variability at interannual, seasonal, and spatial scales. The fall of 2015 was the warmer period (21.96 ± 0.3°C), followed by the spring of 2016 (21.74 ± 0.25°C), both periods coinciding with the highest values of the Multivariate El Niño Index for the study period (see Dıáz-Astudillo et al, 2022). In contrast, the coldest periods were the spring of 2010 (20.02 ± 0.26°C) and 2014 (20.06 ± 0.33°C).…”

“…The HCS is subject to climate perturbations that account for most of the interannual environmental variability (Thomas et al, 2009;Di Lorenzo et al, 2013). During the study period, both ENSO and PDO indices shifted from negative (2010-2013) to positive (2014)(2015)(2016), and then to neutral values (2017), with consequent fluctuations in water temperature, along-shore wind stress, and satellite chlorophyll-a (Dıáz-Astudillo et al, 2022). Thermal fluctuations associated with climate oscillations and/or heatwaves tend to modulate interannual changes in euphausiid assemblages of upwelling systems (Pareś-Escobar et al, 2018;Lilly and Ohman, 2021;Phillips et al, 2022).…”

“…The area presents a generally narrow continental shelf, with no river discharges. Along-shore winds are dominant and sustain intense upwelling year-round, which produces a very shallow oxygen minimum zone (OMZ) and chlorophyll-a filaments that extend several kilometers offshore (for a more detailed description of the study area please refer to Dıáz-Astudillo et al, 2022). The in situ data used in this study (i.e., euphausiid abundance, anchovy biomass and CTD-O (conductivity, temperature, depth and, oxygen) data) were collected during 16 research cruises, conducted every austral fall (8 in April each year) and austral spring (8 in December each year) from 2010 to 2017 onboard the R/V Abate Molina by the Instituto de Fomento Pesquero (IFOP).…”

“…Warm events can also modify the phenology and intensity of primary productivity peaks (Thomas et al, 2009). Consequently, the abundance of cold-water species decreases, and reproductive processes are delayed and/or altered (Dıáz-Astudillo et al, 2022;Killeen et al, 2022). In the HCS, climate events affect net primary productivity and zooplankton communities by modifying species composition and increasing species diversity (Aroneś et al, 2009;Thomas et al, 2009;Escribano et al, 2012).…”