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Predicting species distribution in the ocean has become a crucial task to assess marine ecosystem responses to ongoing climate change. In the Humboldt Current System (HCS), the endemic copepod Calanus chilensis is one of the key species bioindicator of productivity and water masses. Here we modeled the geographic distribution of Calanus chilensis for two bathymetric ranges, 0–200 and 200–400 m. For the 0–200 m layer, we used the Bayesian Additive Regression Trees (BART) method, whereas, for the 200–400 m layer, we used the Ensembles of Small Models (ESMs) method and then projected the models into two future scenarios to assess changes in geographic distribution patterns. The models were evaluated using the multi-metric approach. We identified that chlorophyll-a (0.34), Mixed Layer Depth (0.302) and salinity (0.36) explained the distribution of C. chilensis. The geographic prediction of the BART model revealed a continuous distribution from Ecuador to the southernmost area of South America for the 0–200 m depth range, whereas the ESM model indicated a discontinuous distribution with greater suitability for the coast of Chile for the 200–400 m depth range. A reduction of the distribution range of C. chilensis is projected in the future. Our study suggests that the distribution of C. chilensis is conditioned by productivity and mesoscale processes, with both processes closely related to upwelling intensity. These models serve as a tool for proposing indicators of changes in the ocean. We further propose that the species C. chilensis is a high productivity and low salinity indicator at the HCS. We recommend further examining multiple spatial and temporal scales for stronger inference. [ABSTRACT FROM AUTHOR]

Eastern boundary upwelling systems (EBUS) are highly productive and climatically sensitive ecosystems of the ocean. A critical component sustaining EBUS is the zooplankton secondary production (ZSP) which links primary production (PP) and the higher trophic levels. However, estimating ZSP is a complex task and many questions remain regarding its controlling factors. Here, we used automated analysis to assess taxonomic-structured biomass of zooplankton from a time series (2003–2012) at a fixed station off central-southern Chile. Zooplankton biomasses combined with empirically estimated growth rates, as a function of temperature, Chorophyll-a concentration, and body size, were used to estimate seasonal and interannual changes in ZSP. The annual integrated ZSP yielded a mean of 8.0 g C m−2 y−1, with a minimum in 2009 of 5.7 g C m−2 y−1 and a maximum in 2011 of 13 g C m−2 y−1, and an average annual P/B ratio of 35. The transfer efficiency from PP to ZSP was only 0.8%, indicating a surplus of PP to the system and/or the importance of intermediate microzooplankton levels. Seasonal variation in biomass, ZSP and the P/B ratio were explained mostly by changes in taxonomic structure while interannual variation reflected large-scale climatic changes, such as the Pacific decadal oscillation. [ABSTRACT FROM AUTHOR]

The trophic structure of deep-sea fish communities has been poorly studied in the Southeastern Pacific Ocean. Here, using the analysis of multiple (CNS) stable isotopes, we provide a first approach to characterize the structure of a marine food web including mesopelagic (9 species) and demersal (13 species) fishes. At a species level, Dissostichus eleginoides were the most 13C-depleted and the grenadier Coryphaenoides ariommus the most 13C-enriched species. The most 15N-depleted species was the lanternfish Diogenichthys laternatus and macrourid fishes Trachyrincus villagai and C. ariommus the most 15N-enriched. δ34S values showed less variation, but ranged considerably, varying between 10.5 and 17.7‰: C. ariommus was the most 34S-depleted species and D. eleginoides the most 34S-enriched. At a whole study level, individual δ13C and δ15N values were positively correlated. Relationships between δ13C and δ34S, and δ15N and δ34S were both negative. When analyses were conducted separately for demersal and mesopelagic fishes, δ13C showed a positive correlation with δ15N. There was a negative relationship between δ13C and δ34S in demersal fish but no apparent relationship between δ15N and δ34S. In mesopelagic fishes, there was no statistical support for relationships between δ13C and δ34S or δ15N and δ34S. Mean log-transformed total length (TL) and mean δ15N were related in mesopelagic fishes, but there was no apparent relationship between TL and δ13C or δ34S values. In the case of demersal fishes there was no relationship between TL and either δ15N, δ13C or δ34S. Using cluster analysis, species were classified into 4 distinct trophic groups (G1 - G4) that display different trophic strategies according to the literature. Groups G1 and G2 included zooplanktivorous, micronektonivorous and gelatinovorous fishes associated with pelagic habitats. Groups G3 and G4 include micronektonivorous, piscivorous and generalist fishes foraging in benthic habitats. The demersal fish Dissostichus eleginoides was classified as a member of G1, suggesting that its diet in northern Chile is likely dominated by pelagic prey. In addition, Macrourus holotrachys (G3) showed very marked individual variability in δ15N values indicating considerable intraspecific variation in diet and foraging behavior. Given that this species had isotope values that extended across values typical of benthic and pelagic habitats, it suggests that some individuals may perform vertical migrations. Our results also highlighted that some demersal species (M. holotrachys and Coryphaenoides ariommus) had δ34S values that indicate the assimilation of some chemosynthetic-derived sulfur. Our results provide isotopic information on deep-water species in this region and show likely coupling between the demersal and mesopelagic assemblages. This information improves our understanding of deep-sea ecosystem functioning and provides key information for fisheries management and conservation initiatives. [Display omitted] • First study of multiple (CNS) stable isotopes in deep-sea fishes from the South Eastern Pacific. • The role of coastal upwelling in the N enrichment is proposed. • Macrourus holotrachys seem to be a fish with dietary vertical migrations. [ABSTRACT FROM AUTHOR]

A total of 106 specimens of the big eye grenadier, Macrourus holotrachys , were obtained from 2015 to 2019 as bycatch from the artisanal fishery for Patagonian toothfish (Dissostichus eleginoides) at depths between 1000 and 2200 m in Northern Chile (app. 22°S 70°W). All individuals were examined for their endoparasite fauna and diets. A total of twenty-five parasite taxa (e.g. fifteen Digenea, six Nematoda, three Cestoda, and one Acanthocephala) were found. Twenty taxa were found as adults, four species were found in the larval stage, and one species was found in both the larval and adult stages. Hysterothylacium sp. (Nematoda); Trypanorhyncha gen. sp. (Cestoda); and Monorchiinae gen. sp. (Digenea) were the predominant species, which had a prevalence of 64.2%, 42.5% and 31.1%, respectively. The diet of M. holotrachys included thirteen item-prey, Decapoda and Ophiuridae showed the highest frequency of occurrence (66.3% and 43.3% respectively). A multivariate canonical correspondence analysis (CCA) showed that the association between endoparasites and diet of M. holotrachys explained 45.1% of the total variance. The detected parasite community consisted of parasites linked to benthic, benthopelagic and pelagic environments. This suggests the role of M. holotrachys as a predator of communities close to the seabed but also within the water column, performing vertical and horizontal migrations in the South Eastern Pacific Ocean. [Display omitted] • First study on the diversity of trophically transmitted parasites and diet of Macrourus holotrachys. • Overall a rich trophically transmitted parasite fauna, dominated by Digenea. • Detailed parasite-prey relationships have been suggested. • Potential transmission pathways have been proposed for the recovered parasites. [ABSTRACT FROM AUTHOR]

Seasonal differences in the concentration and biochemical composition of seston have been assessed for the first time in the Humboldt Current System off northern Chile (21°S). The study comprised four seasonal surveys in the Bay of Chipana, including the summer and winter of 2006 and 2007, when El Niño 2006 and La Niña 2007 developed. Protein, lipid, carbohydrate and biogenic silica contents were measured in samples collected at four selected depths. The highest protein, lipid and carbohydrate concentrations were found at the fluorescence maximum (between 10 and 15 m depth), whereas the highest biogenic silica concentration was found 1 m above the seabed. When El Niño started developing, every variable showed low values throughout the water column; however, the lowest values were found when La Niña conditions dominated, together with low oxygen concentrations. Samples collected within the oxygen minimum zone (65 m depth) showed the lowest values for the water column and the lowest seasonal variations. After the evident decline coincident with El Niño 2006, the abundance and biochemical quality (high protein and lipid contents) of seston recovered earlier in the surface layer (upper 15 m) than at other depths. [ABSTRACT FROM PUBLISHER]

The article discusses a study on microbial assemblages in the upwelling system off Concepción, Chile from 2002 to 2003. It analyzes the relationship of virioplankton (VP) abundance/biomass to bakterioplankton (BP), autotrophic (ANF) and heterotrophic (HNF), cholorophyll-a abundance/biomass. Samples taken from off Concepcion area were studied on board the R/V Kay-Kay ship. The study showed that only VP abundance appear to be influenced by upwelling conditions and suggests that viruses may be playing another type of top-down control in the upwelling system.

Abstract: The coastal upwelling ecosystem of the Humboldt Current System off Peru and Chile exhibits strong interannual variability due to changes in the oceanographic conditions related to the El Niño (EN) Southern Oscillation. It is generally believed that major changes occur in the community structure and biological production of this system as a consequence of El Niño-La Niña periods. This paper presents a summary of the information available on the physical, chemical, and biological responses of the Chilean upwelling zone resulting from the strong 1997–1998 EN event. Oceanographic changes for the whole region included the intrusion of oceanic, low-nutrient, warmer, and more oxygenated waters into the coastal areas, with positive sea-surface temperature anomalies lasting until the winter of 1998. Off northern Chile, small-sized phytoplankton prevailed and chlorophyll-a fluctuated widely during most of the EN event, although inshore levels were consistently high. Zooplankton assemblages shifted to smaller species during the warm phase; the total biomass, however, did not change. Primary production rates and the vertical flux of carbon were not greatly affected. The total anchovy catch for 1997 held stable, reaching up to 1 million tons. In 1998, the catch decreased to 400,000tons before recovering to 1.2 million tons in 1999 and 2000. Off central/southern Chile, the ‘normal’ seasonal regime (spring/summer benthic hypoxia) was replaced by oxygenation near the bottom and lower carbon input as a result of the EN event. Macrofaunal biomass increased significantly in the inshore sediments during the warm phase, then diminished in the following spring/summer period. The decreased macrofaunal biomass was associated with the disappearance of filamentous bacterial mats and increased benthic bioturbation. The overall productive capacity of the Chilean upwelling systems seems to have recovered rapidly after the EN decline, suggesting weaker ecological impacts than those observed in the seasons after the 1972–1973 and 1982–1983 events. [Copyright &y& Elsevier]

We present an analysis of seasonal variations in the trophic pathways of carbon in a highly productive coastal upwelling region in the Humboldt current system off Chile. Seasonal changes in phytoplankton, protozooplankton, and bacteria biomass, along with rates of primary production (PP), bacterial growth, secondary production, vertical particle fluxes, and feeding by protozooplankton, omnivorous mesozooplankton, and carnivorous gelatinous zooplankton were determined from July 2004 to June 2005. Phytoplankton biomass and PP were maximal during spring/summer months, associated with upwelling episodes. Heterotrophic nanoflagellates (HNF) were the principal consumers of bacteria, removing >100% of their biomass daily. During autumn/winter, the protozooplankton grazed down a large fraction of HNF production (56% to 96% d-1). The mesozooplankton consumed 1-6% of the PP d-1; the different size fractions of copepods were omnivorous mostly during autumn/winter months, and ctenophores preyed most strongly on small copepods (0.5% to 5% d-1). A large part of the PP was channeled through the microbial food web, and only a small part directly to copepods via the herbivore food chain. The microbial food web transfers bacterial or small algal carbon to protozooplankton, and then to mesozooplankton, and a large percentage of this carbon is also available for the gelatinous predators. Because zooplankton are not able to feed on dissolved organic matter and cyanobacteria, the combined feeding activity of zooplankton either by direct (phytoplankton) or indirect (microbial) pathways increases the yield of PP reaching the zooplankton and, eventually, the upper trophic levels. Our findings suggest that the carrying capacity for larger omnivorous and carnivorous metazoans, and even for commercially exploitable pelagic fishes, might be considerably larger than that expected from a simple herbivore-dominated food chain in coastal upwelling areas [ABSTRACT FROM AUTHOR]

Temporal variability in the daily growth rate (DGR) of the Humboldt Current krill, Euphausia mucronata , was studied in eighteen incubation experiments off the coast of Dichato, central Chile (36.5°S), carried out in 2011–2014. Intermolt period (IMP) was derived from the molting rate method in order to estimate the DGRs. Mean IMP was 9.2 ± 4.8 days (range: 2.9–18.7 d). Overall mean DGR was 0.03 ± 0.13 mm d − 1 . DGR showed a dome-shaped pattern, with a higher mean DGR when upwelling was moderate (0.06 ± 0.04 mm d − 1 ) than intense (0.01 ± 0.00 mm d − 1 ) or weak (0.01 ± − 0.01 mm d − 1 ). This dome-shaped trend was observed in chlorophyll- a concentrations (Chla) at similar upwelling regimens. E. mucronata DGR variability was best explained by a generalized linear model which included the contribution of the Equatorial Subsurface Water, temperature, dissolved oxygen and Chla as predictor variables. Results suggest that E. mucronata is better adapted to grow under upwelling conditions when it can take advantage of high biological productivity, although the species growth is not limited when weak upwelling or even downwelling occurs. Analysis of the duration of the upwelling events suggest that E. mucronata growth is limited (shrinking) when upwellings last > 10 days. [ABSTRACT FROM AUTHOR]

The structure of the pelagic food web is a key issue to understand the variability in C and N fluxes in the ocean. The trophic structure of the hyperiid amphipods and its spatial variation in the subtropical area of the Southeast Pacific was studied based on C and N isotope composition. Zooplankton were collected off northern and Central-southern Chile during September-November 2016 at the coastal zone and in oceanic areas. Measurements of δ15N and δ13C of individual hyperiids were used to estimate the trophic position for each species, and to assess the community isotopic niche for 3 pre-defined areas: the coastal upwelling (eutrophic) zone, the coastal transition (mesotrophic) zone and the oceanic (oligotrophic) zone, as well as three depth layers. Our results showed different assemblages of species among the 3 zones, but also a large overlap between the isotopic niche for all zones and depth layers. In the mesotrophic zone there was a noticeable increase in the trophic position of individual species. The trophic diversity of hyperiids over the study region was relatively high, including primary consumers, omnivores and carnivorous feeders, and was associated with the changes in productivity across zones. However, carnivory was more prevalent in the mesotrophic zone and in the mesopelagic (500–1000 m) layer. We suggest that such variations reflect both the biogeochemical processes controlling the productivity in each zone, and the life-traits of individual species. • Hyperiid assemblages are different according to productivity zones. • Hyperiids amphipods are more enriched in δ15N and δ13C in the EZ. • Isotopic niche of hyperiids display large overlap among zones and among depth layers. • Hyperiids amphipods niche size decreased from EZ to OZ. • Trophic position of hyperiid assemblages were similar among zones. [ABSTRACT FROM AUTHOR]

Oxygen Minimum Zones (OMZ's) are expanding and intensifying as result of climate change, affecting Eastern Boundary Upwelling Systems. Local effects of vertical movements of OMZ's that result from changes in upwelling intensity could reduce or expand the oxygenated surface layer that most zooplanktonic species inhabit in coastal areas. Using the copepods Calanus chilensis and Acartia tonsa as model organisms, an experimental test of the impact of different dissolved oxygen (DO) concentrations (between 0.5 and 5 ml L − 1 ) on egg production and hatching success was carried out and compared with field estimations of egg production, female and egg abundance in Mejillones Bay (23°S). Abundance of C. chilensis was highly variability and no consistent pattern in egg production and hatching success was found across DO levels, whereas A. tonsa egg production had maximum values between 2.6 and 4.7 ml O 2 L − 1 and hatching success was positively correlated with DO (r = 0.75). In the field, temperature was the main factor controlling the dynamics of both species, while Chl- a and DO were also correlated with C. chilensis and A. tonsa , respectively. Principal Component Analysis showed that abundances of both copepods were controlled by temperature, stratification, OMZ depth, and Ekman transport, which together explained more than 70% of the total variance and were the main factors that modulated the populations of C. chilensi s and A. tonsa in the upwelling zone of northern Chile (23°S). The differential responses of C. chilensis and A. tonsa to changes in DO concentrations associated with vertical movements of the OMZ suggest that C. chilensis may be better adapted to hypoxic conditions than A. tonsa , however both species are successful and persistent all year-round. We suggest that physiological responses of copepods could be used to evaluate population dynamics affected by the shoaling of OMZ's and the repercussions to trophic food webs of eastern boundary current systems. [ABSTRACT FROM AUTHOR]

Abstract: This study assesses the spatial and temporal patterns of the euphausiid community from the coastal upwelling zone and oceanic areas of central-southern Chile, surveyed between August 2007 and November 2008. A total of 22 species were found, most of them already described for the region. The numerically dominant species was Euphausia mucronata for the entire study area (>60%), which was found in more oceanic waters (>90°W), thereby expanding its longitudinal distribution range. The species showed distinct spatial distribution patterns, allowing its classification as a coastal, oceanic, southern and northern species. The community descriptors – species richness, total abundance, Pielou and Shannon index – all had patterns associated with the cross-shelf and alongshore axes. Over a temporal scale, species abundance and community descriptors showed strong seasonal patterns. Abundances decreased offshore but diversity increased towards the oceanic area, revealing an inverse relationship between total abundance and the Shannon index. Diversity was positively related to sea surface temperature. Although the most abundant species were concentrated within the coastal zone, euphausiid abundance and diversity in the oceanic region were high. Our findings suggest that the high productivity of the upwelling region may sustain the euphausiid populations in the coastal transition zone and in the offshore region, and that high abundance and diversity across the entire region may be maintained by a highly heterogeneous environment promoted by upwelling, giving rise to an increased number of potential ecological niches. [Copyright &y& Elsevier]

The loss of biodiversity in marine populations is one of the consequences of the increased events of extreme environmental conditions in the oceans, which can condition the persistence of populations to future scenarios of climate change. Therefore, it is extremely necessary to explore and monitor the genetic diversity of natural populations. In the Southeast Pacific Ocean (SEPO), specifically on the coast of Chile, the presence of the copepod Acartia tonsa has been indicated solely using morphological evidence, due to the absence of genetic information. In the present work, the genetic diversity, population structure and phylogenetic position within the genus Acartia, of populations identified morphologically as A. tonsa, was evaluated by amplification of the mitochondrial cytochrome c oxidase subunit I and nuclear marker 18 s. Our results showed that the populations identified as A. tonsa correspond to a new monophyletic group endemic to SEPO (GMYC = 1.00; PTP = 0.95). The populations showed moderate to high genetic diversity with an incipient structuring between populations and biogeographic zones. Our results suggest that despite the homogenizing effect of the Humboldt Current, isolation by distance and contrasting environmental conditions at different geographic scales have an important influence on the genetic diversity of zooplankton in the SEPO region., (© 2024. The Author(s).)

Two deep-sea shark species were obtained as by-catch of the local fishery of the Patagonian toothfish, Dissostichus eleginoides, at depths ranging from 1000 to 2200 m off central and northern Chile. A total of 19 parasite taxa were found in 133 specimens of the southern lanternshark, Etmopterus granulosus, (n = 120) and largenose catshark, Apristurus nasutus, (n = 13). Fourteen taxa (four Monogenea, one Digenea, four Cestoda, one Nematoda, two Copepoda, one Annelida and one Thecostraca) were found in E. granulosus, whereas five taxa (one Monogenea, two Cestoda and two Nematoda) were found in A. nasutus. Representatives of Cestoda showed higher values of prevalence and a greater intensity of infection; this pattern is consistent with reports for elasmobranchs, but the monogenean richness was higher than that previously reported for related deep-sea sharks. Regarding E. granulosus, a positive and significant correlation between host length and abundance was found for six (four ectoparasites, one mesoparasite, and one endoparasite) of the 14 taxa recorded, but prevalence was significantly correlated with host length only for the monogenean Asthenocotyle sp. Although the sample size for A. nasutus was limited, we compared richness, abundance, diversity and evenness at the infracommunity and component community levels. All of these variables were higher for E. granulosus, but at the infracommunity level, abundance was higher for A. nasutus. All the parasite taxa (except two) represent new host and geographical records., (© J.F. Espínola-Novelo et al., published by EDP Sciences, 2018.)