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(searched for: doi:10.3354/sedao00014)
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ICES Journal of Marine Science, Volume 79, pp 61-75; https://doi.org/10.1093/icesjms/fsab241

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.
Journal of Plankton Research, Volume 43, pp 712-724; https://doi.org/10.1093/plankt/fbab059

Abstract:
Cnidarian jellyfish can be dominant players in the food webs of highly productive Eastern Boundary Currents (EBC). However, the trophic role of inconspicuous hydromedusae in EBCs has traditionally been overlooked. We collected mesozooplankton from five stations along two cross-shelf transects in the Northern California Current (NCC) during winter and summer of 2018–2019. We analyzed gut contents of 11 hydromedusan species and the prey community to (i) determine prey resource use by hydromedusae and (ii) determine temporal shifts in the trophic niche of hydromedusae, focusing on the two most collected species (Clytia gregaria and Eutonina indicans). Hydromedusae in the NCC fed mostly on copepods, appendicularians and invertebrate larvae. Nonmetric multidimensional scaling of hydromedusan diets showed seasonal shifts in prey resource driven by the abundant C. gregaria, which fed mostly on copepod eggs during winter and fed mostly on appendicularians and copepods during summer. Prey selectivity for copepod eggs increased during winter for C. gregaria and E. indicans. Intriguingly, theoretical ingestion rates show that both species acquire similar amounts of carbon during upwelling and nonupwelling conditions. Hydromedusae’s consistent presence and predation impact across seasons may lead to significant effects in carbon and energy transfer through the NCC food web.
, Kim Hünerlage, Thorsten Werner
Published: 24 March 2020
Frontiers in Physiology, Volume 11; https://doi.org/10.3389/fphys.2020.00248

Abstract:
Oxygen Minimum Zones prevail in most of the world’s oceans and are particularly extensive in Eastern Boundary Upwelling Ecosystems such as the Humboldt and the Benguela upwelling systems. In these regions, euphausiids are an important trophic link between primary producers and higher trophic levels. The species are known as pronounced diel vertical migrators, thus facing different levels of oxygen and temperature within a 24 h cycle. Declining oxygen levels may lead to vertically constrained habitats in euphausiids, which consequently will affect several trophic levels in the food web of the respective ecosystem. By using the regulation index (RI), the present study aimed at investigating the hypoxia tolerances of different euphausiid species from Atlantic, Pacific as well as from Polar regions. RI was calculated from 141 data sets and used to differentiate between respiration strategies using median and quartile (Q) values: low degree of oxyregulation (0.25 < RI median < 0.5); high degree of oxyregulation (0.5 < RI median < 1; Q1 > 0.25 or Q3 > 0.75); and metabolic suppression (RI median, Q1 and Q3 < 0). RI values of the polar (Euphausia superba, Thysanoessa inermis) and sub-tropical (Euphausia hanseni, Nyctiphanes capensis, and Nematoscelis megalops) species indicate a high degree of oxyregulation, whereas almost perfect oxyconformity (RI median ≈ 0; Q1 < 0 and Q3 > 0) was identified for the neritic temperate species Thysanoessa spinifera and the tropical species Euphausia lamelligera. RI values of Euphausia distinguenda and the Humboldt species Euphausia mucronata qualified these as metabolic suppressors. RI showed a significant impact of temperature on the respiration strategy of E. hanseni from oxyregulation to metabolic suppression. The species’ estimated hypoxia tolerances and the degree of oxyconformity vs. oxyregulation were linked to diel vertical migration behavior and the temperature experienced during migration. The results highlight that the euphausiid species investigated have evolved various strategies to deal with different levels of oxygen, ranging from species showing a high degree of oxyconformity to strong oxyregulation. Neritic species may be more affected by hypoxia, as these are often short-distance-migrators and only adapted to a narrow range of environmental conditions.
, Jaime Gómez-Gutiérrez, María Del Carmen Franco-Gordo, Viridiana Plascencia-Palomera, , , Bertha E. Lavaniegos
Published: 24 August 2018
Continental Shelf Research, Volume 168, pp 54-67; https://doi.org/10.1016/j.csr.2018.08.007

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Jaime Gómez-Gutiérrez, José Raúl Morales-Ávila, So Kawaguchi
Global Diversity and Ecological Function of Parasites of Euphausiids pp 17-38; https://doi.org/10.1007/978-3-319-41055-5_2

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, Jaime Gómez-Gutiérrez, Jocelyn Silva-Aburto, , Wolfgang Schneider
Published: 22 May 2017
Invertebrate Biology, Volume 136, pp 260-270; https://doi.org/10.1111/ivb.12176

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, Carmen Franco-Gordo, Ricardo Palomares-García, Jaime Gómez-Gutiérrez, Eduardo Suárez-Morales
Estuarine, Coastal and Shelf Science, Volume 184, pp 138-150; https://doi.org/10.1016/j.ecss.2016.11.012

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