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Oceanic islands and seamounts are considered biodiversity hotspots. Here, we present a taxonomy and community analyses of hyperiid amphipods collected near oceanic islands and over seamounts of the Juan Fernández Archipelago and Desventuradas Archipelago in the South-east Pacific. Both archipelagos are separated by about 800 km over the meridional gradient, suggesting the existence of different hyperiid communities because of apparent geographic isolation and distinctive oceanographic characteristics between regions. To test this hypothesis, zooplankton samples were collected from 19 stations during the CIMAR 22 ‘Oceanic Island’ cruise in October–November 2016. In total, 56 species of hyperiids were found, of which Phrosina semilunata, Lestrigonus schizogeneios, Hyperietta stephenseni, Hyperioides longipes, Phronimella elongata and Primno latreillei were the most abundant and recurrent species. The species richness (S), Shannon–Wiener diversity (H’) and dominance (D) of both the archipelagos were not significantly different. Additionally, except for a small group of rare species, the species composition was similar in both areas. Most species showed greater abundances than those observed in the coastal upwelling zone off Chile, whereas shared species between regions suggested the presence of a single biogeographic unit comprising the coastal transition zone and oceanic area off Chile within which both archipelagos are included. Correlation analysis indicated that salinity was the best predictor for the community structure, which provides evidence that the contributions of previously described water masses of the South-east Pacific may influence the spatial distribution and composition of the hyperiid community.

A select group of marine organisms can enter the Oxygen Minimum Zones (OMZs) and even anoxic waters, while performing diel vertical migration (DVM). DVM of the euphausiid Euphausia eximia off northern Chile in the spring of 2015 was documented based on acoustic measurements using an echo sounder along with net samplings. Dissolved oxygen (DO) concentrations were obtained using a vertical profiler, and water samples were collected to obtain in situ nitrite (NO2−) concentrations as well as pHT, total alkalinity (AT), and therefore carbon dioxide partial pressure (pCO2) was estimated. Krill were found to migrate up to the surface (0–50 m) during the night and returned to ca. 200–300 m depth during the day, spending between 11 and 14 h at these layers. At the surface, DO and NO2− concentrations were 208 and 0.14 μM respectively, while pHT was 8.04 and 405 μatm pCO2. In contrast, at the deeper layers (200–300 m), DO and NO2− were T 7.53 and 1490 μatm pCO2. The pHT and high pCO2 values at depths represent the conditions predicted for open ocean waters in a worst-case global warming scenario by 2150. The acoustic scatter suggested that > 60% of the krill swarms enter the OMZ and anoxic waters during the daytime. These frequent migrations suggest that krill can tolerate such extreme conditions associated with anoxic and high-pCO2 waters. The inferences drawn from the observation of these migrations might have strong implications for the current oceanic carbon pump models, highlighting the need for understanding the molecular and physiological adaptations allowing these migrations.

Respiration is a key process in the cycling of particulate matter and, therefore, an important control mechanism of carbon export to the ocean's interior. Most of the fixed carbon is lost in the upper ocean, and only a minor amount of organic material sustains life in the deep-sea. Conditions are particularly extreme in hadal trenches, and yet they host active biological communities. The source of organic carbon that supports them and the contribution of these communities to the ocean carbon cycle, however, remain uncertain. Here we report on size-fractionated depth profiles of plankton respiration assessed from the activity of the electron transport system in the Atacama Trench region, and provide estimates of the minimum carbon flux (FC) needed to sustain the respiratory requirements from the ocean surface to hadal waters of the trench and shallower nearby sites. Plankton < 100 μm contributed about 90% to total community respiration, whose magnitude was highly correlated with surface productivity. Remineralization rates were highest in the euphotic zone and declined sharply within intermediate oxygen-depleted waters, remaining fairly constant toward the bottom. Integrated respiration in ultra-deep waters (> 1000 m) was comparable to that found in upper layers, with 1.3 ± 0.4 mmol C m−2 d−1 being respired in the hadopelagic. The comparison between our FC models and estimates of sinking particle flux revealed a carbon imbalance through the mesopelagic that was paradoxically reduced at greater depths. We argue that large fast-sinking particles originated in the overlying surface ocean may effectively sustain the respiratory carbon demands in this ultra-deep marine environment.

This paper focuses on the calibration of heat source parameters to reproduce temperatures and distortions in welded joints. Specifically, the proposed methodology, which combines the Finite Element Method and Design of Experiments, is applied to calibrate a T-joint dissimilar titanium laser welding process. The thermal problem is addressed using a 3D transient model with a Conical Gaussian heat flux, and the mechanical problem is tackled using a 3D elastic-plastic model. A Fractional-Factorial Design is performed to define a set of thermo-mechanical uncoupled models. Finally, optimal parameter combinations that replicate experimental data are identified. This methodology allows automation that replaces the traditional trial and error process, which frequently does not provide good results, is an exhausting task and requires a dubious amount of time.

The subtropical gyres occupy approximately 40% of the surface of the Earth and are widely recognized as oligotrophic zones. Among them, the South Pacific subtropical gyre (SPSG) shows the lowest chlorophyll-a levels (0.02–0.04 μgL–1), the deepest nutricline (>200 m) and euphotic zone (∼160 m), and the lowest rates of nitrogen fixation. The zooplankton community is poorly known in the SPSG. We report a study focused on the composition and distribution of pelagic copepods within the gyre so as to uncover the diversity and habitat conditions of this special community. Therefore, during the austral spring of 2015, an oceanographic cruise was conducted across the eastern side of the SPSG. Physical and chemical variables were measured in the upper 1000 m, while zooplankton samples were collected by means of vertically stratified hauls using a multiple net sampler for five layers (0–800 m). Satellite data were also used to assess near-surface phytoplankton biomass (Chl-a) and physical-dynamics conditions during the cruise, and 121 species of copepods were identified, which belonged to five taxonomic orders, 24 families, and 50 genera. Calanoida and Cyclopoida were the most frequent orders, containing 57% and 38% of species, respectively, whereas Harpacticoida and Mormonilloida contained 2% of species each, and Siphonostomatoida contained 1% of species. The vertical distribution of copepods revealed an ecological zonation linked to a strongly stratified water column, such that three different vertical habitats were defined: shallow (0–200 m), intermediate (200–400 m), and deep (400–800 m). Both the abundance and diversity of copepods were greater in the shallow habitat and were strongly associated with water temperature, whereas copepods in the subsurface layers subsisted with relatively low oxygen waters (2–3 mL O2 L–1) and presumably originated at the Chilean upwelling zone, being transported offshore by mesoscale eddies. Furthermore, the analysis of species composition revealed a marked dominance of small-sized copepods, which may play a key role in nutrient recycling under an oligotrophic condition, as inferred from their mostly omnivorous feeding behavior. Our findings also suggested a potentially high endemism within the gyre, although basin-scale circulation and mesoscale eddies, traveling from the coastal upwelling zone and transporting plankton, can also influence the epipelagic fauna.

Eurythenes S.I. Smith in Scudder, 1882 (Crustacea: Amphipoda) are prevalent scavengers of the benthopelagic community from bathyal to hadal depths. While a well-studied genus, molecular systematic studies have uncovered cryptic speciation and multiple undescribed lineages. Here, we apply an integrative taxonomic approach and describe the tenth species, Eurythenes atacamensis sp. nov., based on specimens from the 2018 Atacamex and RV Sonne SO261 Expeditions to the southern sector of the Peru-Chile Trench, the Atacama Trench (24–⁠21°S). Eurythenes atacamensis sp. nov. is a large species, max. observed length 83.2 mm, possesses diagnostic features, including a short gnathopod 1 palm and a chelate gnathopod 2 palm, and a distinct genetic lineage based on a 16S rRNA and COI phylogeny. This species is a dominant bait-attending fauna with an extensive bathymetric range, spanning from 4974 to 8081 m. The RV Sonne SO261 specimens were recovered along a 10-station transect from abyssal to hadal depths and further examined for demographic and bathymetric-related patterns. Ontogenetic vertical stratification was evident across the trench axis, with only juveniles present at abyssal depths (4974–6025 m). Total length-depth analysis revealed that the size of females was unrelated to depth, whereas juveniles followed a sigmoidal relationship with a step-up in size at depths >7200 m. Thus, these bathymetric trends suggest that juveniles and females employ differing ecological strategies in subduction trench environments. This study highlights that even dominant and ecologically important species are still being discovered within the abyssal and hadal environments. Continued systematic expeditions will lead to an improved understanding of the eco-evolutionary drivers of speciation in the world’s largest ecosystem.

The subtropical region of the Southeast Pacific exhibits a strong onshore-offshore gradient in hydrographic conditions and biological production from the eutrophic upwelling zone to the ultra-oligotrophic oceanic area in the central South Pacific gyre (SPG). Across this gradient, zooplankton must cope with either gradual or abrupt changes in environmental conditions. Here, the distribution and diversity of hyperiid amphipods were assessed over this gradient in the upper 1000 m in relation to temperature, salinity, oxygen, chlorophyll-a, sea level anomalies, the bulk of mesozooplankton biomass and the biomass of salps, siphonophores, and other hydrozoans during October/November 2015 from the coastal zone off Chile (27° 00‵ S, 70° 52‵ W) to near Easter Island within the SPG (27° 10‵ S, 109° 20‵ W). The most frequent and abundant species were Hyperioides longipes Chevreux, 1900, Eupronoe minuta Claus, 1879, and Hyperioides sibaginis (Stebbing, 1888). Significant changes in abundance and community structure across the gradient with respect to the evaluated environmental variables and significant correlations of 17 hyperiid species with the gelatinous category other hydrozoans were found. These changes were closely linked to previously defined zonation patterns, which contained distinct species assemblages and a unique dominant species per zone. These zones represented ecoregions based on diversity patterns of hyperiids and other shared species among such ecoregions suggesting a possible ecological connectivity among the zones, promoted by mesoscale eddies travelling westward from the coastal upwelling zone to offshore waters. Environmentally forced zonation and the interactions with mesoscale features are thus suggested as the driving processes maintaining spatial patterns of diversity of the hyperiid community in the Southeast Pacific.

BackgroundCurrently, 24 species of Encotyllabe Diesing, 1850 (Monogenea: Capsalidae) are listed in WoRMS, but the validity of many species has been questioned due to deficient or incomplete descriptions. On the other hand, almost all species in the genus have been described from one host species or closely related host species, suggesting host specificity, but other species, specifically Encotyllabe spari Yamaguti, 1934, have been reported at least from 19 species belonging to nine families in two orders (Perciformes and Scorpaeniformes) from Japan, the Arabian Gulf and Brazil. Concerning Brazilian records of Encotyllabe spari (but also as Encotyllabe cf. spari); seven host species belonging to four families and two orders have been reported as hosts for this species. The aim of this study was to describe two new species of Encotyllabe from Brazil, previously considered as E. spari.MethodsDuring 2016, we examined specimens of Orthophristis ruber (Cuvier) (Haemulidae) and Pagrus pagrus (Linnaeus) (Sparidae) caught off the coast of Cabo Frio, Rio de Janeiro, Brazil by local fishermen. Specimens of Encotyllabe were collected from the pharyngeal plates of the hosts. Morphological and morphometric (multivariate analysis of proportional measurements standardized by total length) and molecular analysis (LSU rRNA and cox1 gene) were performed in order to identify the collected monogenea. ResultsThe presence of two new species of Encotyllabe, Encotyllabe yamagutii n. sp. and Encotyllabe haemuli n. sp., parasitizing the pharyngeal plates of Pagrus pagrus and Orthopristis ruber, respectively, is strongly suggested by the three approaches used in this study. The main morphological differences from the most related species include a combination of body size, shape of the penis, and size and position of the testes.ConclusionsSpecimens of Encotyllabe, hitherto recorded as E. spari or E. cf. spari, belong to two new species. Our results suggest that the host specificity for members of Encotyllabe and specimens registered as E. spari, other than those from the original description, must be revisited.

Across boundary currents, zooplankton are subject to strong oceanographic gradients and hence strong selective pressures. How such gradients interact with the speciation process of pelagic organisms is still poorly understood in the open ocean realm. Here we report on genetic diversity within the pelagic copepod Pleuromamma abdominalis in the poorly known Southeast Pacific region, with samples spanning an ocean gradient from coastal upwelling to the oligotrophic South Pacific Subtropical Gyre. We assessed variation in fragments of the mitochondrial (mt) genes cytochrome c oxidase subunit I (COI) and Cytochrome b as well as in the nuclear internal transcribed spacer (ITS) region and 28 S rRNA. Phylogenetic analyses revealed the presence of 8 divergent lineages occurring across the gradient with genetic distances in the range of 0.036 and 0.44 (mt genes), and GMYC species delimitation methods support their inference as distinct (undescribed) species. Genetic lineages occurring across the zonal gradient showed strong genetic structuring, with the presence of at least two new lineages within the coastal upwelling zone, revealing an unexpectedly high level of endemism within the Humboldt Current System. Multivariate analyses found strong correlation between genetic variation and surface chlorophyll-a and salinity, suggesting an important role for hydrographic gradients in maintaining genetic diversity. However, the presence of cryptic lineages within the upwelling zone cannot be easily accounted for by environmental heterogeneity and poses challenging questions for understanding the speciation process for oceanic zooplankton.

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.

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.

Seamounts in the Juan Fernandez Ridge, as well as in other seamount regions in the eastern South Pacific and in the world oceans, remain poorly studied ecosystems in terms of structure and functioning. Here, community respiration by epipelagic mesozooplankton in three seamounts of the Juan Fernandez Ridge, including the O`Higgins Seamount close to the coastal upwelling zone and two oceanic seamounts near the Juan Fernandez Archipelago (~33°S–78°W), was assessed. Oxygen consumption by mixed assemblages was estimated using continuous measurements of dissolved oxygen concentration under controlled temperature during onboard, short-term incubations (2–4 h). Mesozooplankton composition was analyzed with a ZooScan device and expressed in terms of community normalized size spectra, and taxa and size diversity (Shannon-Wiener index). Carbon-specific community respiration rates in the upper 100 m layer were in the range of 0.3–1.9 mg O2 m−2 d−1, indicating that up to 3.1% of the mesozooplankton biomass can be respired on a daily basis. The mesozooplankton community was dominated by small-size copepods but the proportions of small copepods, large copepods, and gelatinous zooplankton (mostly salps) changed between the seamounts, in association with modifications in taxa composition, size diversity, and the slope of the size spectrum. Community respiration was significantly correlated to these community descriptors, suggesting the composition of the pelagic community has a direct impact on the total amount of respired-C. Connectivity between the coastal upwelling zone and the Juan Fernandez Ridge region mediated by mesoscale activity, interacting with the seamounts, is suggested as a most important process in controlling zooplankton community structure and in turn community metabolism.

The Humboldt Current Large Marine Ecosystem (HCLME) is recognised as one of the largest and most productive marine ecosystems. The estimated number of teleost fish species for the Chilean coast influenced by the HCLME reaches c.1,030 but digeneans have been reported for 39 teleost species, i.e. less than 4% of the potential hosts. During a survey of parasites of the Galapagos sheephead wrasse Semicossyphus darwini (Jennyns) (Perciformes: Labridae) from off northern Chile, we obtained representatives of three digenean species, Helicometrina nimia Linton, 1910 (Opecoelidae), Proctoeces humboldti George-Nascimento & Quiroga, 1983 (Fellodistomidae) and Labrifer secundus Manter, 1940 (Lepidapedidae). Labrifer secundus, originally described from Semicossyphus pulcher (Ayres, 1854) off the coast of Baja California, Mexico is re-described. Helicometrina nimia is a common parasite from littoral fishes in the HCLME. Semicossyphus darwini is a new host for these three digenean species.

Deoxygenation of the ocean has become a critical issue in coastal upwelling systems, which are subjected to shallow Oxygen Minimum Zones (OMZs). The OMZ can expand into the photic zone, causing hypoxic conditions and affecting pelagic organisms. During the winters 2013 and 2014, the copepod Calanus chilensis was collected off northern Chile to evaluate how oxygen conditions may affect its vital rates and to assess the physiological responses of developmental stages to oxygen. Adult females, eggs, and early nauplii (N1 to N3) were exposed to hypoxia (~ 32.6 μmol kg − 1 , ~ 2.5 kPa) and normoxia (~ 252.2 μmol kg − 1 , ~ 19.9 kPa) in the laboratory. Survival of females and their egg production were not affected by hypoxia. No significant differences in female somatic growth and potential respiration between hypoxic and normoxic conditions were found. Early stages, however, were strongly affected by hypoxia. Hatching success diminished by at least 29% from normoxia (72.3 ± 6.6% and 55.5 ± 3.7%) to hypoxia (22.9 ± 9.7% and 26.8 ± 6.8%). Naupliar growth was significantly lower under hypoxia (0.15 ± 0.02 d − 1 ) than normoxia (0.24 ± 0.01 d − 1 ). These findings suggest that expansion of OMZs in upwelling systems may substantially influence copepod dynamics by suppressing growth and survival of early life stages.

The role of zooplankton in microbial nitrogen turnover in marine environments is poorly understood. Here, we present results from two experiments designed to determine the excretion rate of ammonium and dissolved organic nitrogen (DON) by dominant copepods, Acartia tonsa and Paracalanus cf indicus, fed with two natural sized-fractioned diets (20–150 μm and

The Humboldt Current krill, Euphausia mucronata (Crustacea: Euphausiacea), is an endemic and keystone species in the food web of this highly productive eastern border current ecosystem. The morphology and ontogeny of E. mucronata is known from calyptopis I to the adult phase, but the embryonic and early-life stages (nauplius and metanauplius) of this broadcast spawning species are unknown. We describe the morphology and development time of these life stages to complete the knowledge of its life cycle. Embryos were obtained from purple-gonad gravid females collected off Dichato, central Chile, during November 2012. Eight gravid females (mean=16 mm total length) were incubated in seawater at 12°C under laboratory conditions. The average development time from single-cell embryos to the metanauplius stage was 2.2 d and hatching occurred between 20 and 25 h. The average growth rate was 0.35 mm d−1 from the late limb bud to the metanauplius stage (range=0.21–0.48 mm d−1). Embryos of E. mucronata had a mean chorion diameter of 0.460 mm, embryo diameter of 0.343 mm, and perivitelline space of 0.056 mm. Our biological information reported here constitutes a baseline for future ecological studies on distribution and temporal variability of spawning activity and reproductive strategies of E. mucronata in the highly variable and productive Humboldt Current ecosystem.

Little is known about the diversity of parasites of the deep-sea fish of the world's oceans. Here, a new species of monogenean parasite of the deep-sea skate Gurgesiella furvescens is described. Specimens of parasites were obtained from the skin of two specimens of the dusky finless skate, G. furvescens (Rajidae), in the vicinity of Valparaiso (33°S, 72°W), central Chile, from midwater trawl fishing at depths of 350–450 m. Both morphological and molecular analyses were conducted to provide a full description of the new species, named Acanthocotyle gurgesiella. For the molecular analyses, nuclear large subunit (LSU) rDNA and the mitochondrial gene cytochrome c oxidase 1 (COI) were used. From the morphological analysis and a comparison with the known species of the genus, A. gurgesiella can be identified by a combination of morphological characteristics, including the number of testes, number of radial rows of sclerites in the pseudohaptor, aperture of the genital pore and shape of the vitelline follicles. The results from the DNA analysis indicated that A. gurgesiella has a genetic divergence of 3.2–3.7% (LSU rDNA gene) from A. urolophi, the only congener species for which molecular data are available.

Crustacean zooplankton, often dominated by copepods and euphausiids, are the major phytoplankton grazers in coastal upwelling systems. It has been argued that grazing by zooplankton is a size-dependent process, such that models incorporating the size structure of zooplankton are appropriate for describing herbivore C-transfer. Here, b ased on the size-spectrum theory and on gut-fluorescence experiments, conducted with numerically dominant copepods from two upwelling sites off the Chilean coast , we show that C-specific ingestion rates of copepods are size-dependent. We further show that the size structure of the copepod community, synthesized by the slope of the normalized size spectrum, determines the impact of grazing on phytoplankton. C-specific ingestion rates, depending on species size, were in the range of 0.02-8.40 (µg C x µg C -1 d -1 ). A modelled normalized biomass-spectra of a copepod community in the size range of 0.5 to 74.0 µg C showed that C-specific grazing impact can increase by a factor of 4 when small-sized species (0.1-10 µg C indiv -1 ), such as Paracalanus cf. indicus , Acartia tonsa , Oncaea spp. and Corycaeus spp., dominate the community in terms of biomass. By contrast, when larger-sized copepods dominate (10-100 µg C indiv -1 ), such as Calanus chilensis , Calanoides patagoniensis and Rhyncalanus nasutus , total zooplankton biomass may increase, but with a sharp decrease in the efficiency of C transfer via herbivores. Our findings indicate that processes affecting the size structure of zooplankton communities can substantially impact on phytoplankton C flux through the pelagic food web, thus controlling production of higher trophic levels.

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.

Background Parasites of deep-sea fishes from the South-East Pacific (SPO) are poorly known. Of c.1030 species of fish found in this area, 100–150 inhabit the deep-sea (deeper than 200 m). Only six articles concerning metazoan parasites of fish from deep-waters of SOP are known, and nine monogenean species have been reported. Currently, ten species are known in Acanthocotyle Monticelli, 1888 (Monogenea) and when stated, all of them are found in shallow waters (10–100 m). Acanthocotyle gurgesiella Ñacari, Sepulveda, Escribano & Oliva, 2018 is the only known species parasitizing deep-sea skates (350–450 m) in the SPO. The aim of this study was the description of two new species of Acanthocotyle from two Rajiformes. Methods In September 2017, we examined specimens of two species of deep-sea skates (Rajiformes), Amblyraja frerichsi (Krefft) and Bathyraja peruana McEachran & Myyake, caught at c.1500 m depth off Tocopilla, northern Chile, as a by-catch of the Patagonian tooth fish Dissostichus eleginoides Smitt fishery. Specimens of Acanthocotyle were collected from the skin of the skates. Morphometric (including multivariate analysis of proportional measurements, standardized by total length), morphological and molecular analyses (LSU rRNA and cox1 genes) were performed in order to identify the collected specimens. Results The three approaches used in this study strongly suggest the presence of two new species in the genus Acanthocotyle: Acanthocotyle imo n. sp. and Acanthocotyle atacamensis n. sp. parasitizing the skin of the thickbody skate Amblyraja frerichsi and the Peruvian skate Bathyraja peruana, respectively. The main morphological differences from the closely related species Acanthocotyle verrilli Goto, 1899 include the number of radial rows of sclerites, the non-discrete vitelline follicles and the number of testes. Conclusions The two species of monogeneans described here are the only recorded parasites from their respective host species in the SPO. Assessing host specificity for members of Acanthocotyle requires clarifying the systematics of Rajiformes.

The daily vertical movement of zooplankton, known as diel vertical migration (DVM), can enhance the vertical flux of carbon (C) and so contributing to the functioning of the biological pump. The magnitude and efficiency of this active transport of C may depend on the size and taxonomic structure of the migrant zooplankton. However, the impact that a variable community structure can have on zooplankton-mediated downward C has not been properly addressed. This taxonomic effect may become critically important in highly productive eastern boundary upwelling systems (EBUS), where zooplankton biomass becomes aggregated in the coastal zone, but comprised by a highly variable community structure (size-composition). In these systems, presence of a subsurface oxygen minimum zone (OMZ) can impose an additional constraint to vertical migration and so influencing the downward C export. Here, we address these issues based on a high-resolution zooplankton sampling at three stations off northern Chile (20°S−30°S) during November 2015. Automated analysis of zooplankton composition and taxa-structured biomass allowed us to estimate daily migrant biomass by taxa, amplitude of migration and daily rate of migration, defined as the daily exchange of biomass between the upper mixed layer and below the thermocline. We found that high biomass aggregates above the oxycline, associated with more oxygenated surface waters and this condition was more evident upon a more intense OMZ. Some taxa however, were found closely associated with the OMZ. We found that most taxa were able to perform DVM in the upwelling zone withstanding severe hypoxia. Even, several strong migrants, such as copepods Eucalanidae and Euphausiids, can exhibit a large migration amplitude (~500 m), remaining either temporarily or permanently during the day or night condition within the core of the OMZ and so contributing to the release of C below the thermocline. Our estimates of DVM-mediated C flux showed that migrant biomass (5099 ± 2701 mg C m−2d−1) may contribute with about 678 ± 465 mg C m−2d−1 to the OMZ system through respiration, mortality, and production of fecal pellets, implying the existence of a very efficient mechanism to incorporate freshly produced C into the OMZ. This downward C by zooplankton is however strongly depending on taxonomic structure due to variable migration amplitude and behavior affecting the daily rate of diel vertical migration.

Global environmental changes are challenging the structure and functioning of ecosystems. However, a mechanistic understanding of how global environmental changes will affect ecosystems is still lacking. The complex and interacting biological and physical processes spanning vast temporal and spatial scales that constitute an ecosystem make this a formidable problem. A unifying framework based on ecological theory, that considers fundamental and realized niches, combined with metabolic, evolutionary, and climate change studies, is needed to provide the mechanistic understanding required to evaluate and forecast the future of marine communities, ecosystems, and their services.

A 10-year time series (2002–2012) at Station 18 off central/southern Chile allowed us to study variations in zooplankton along with interannual variability and trends in oceanographic conditions. We used an automated analysis program (ZooImage) to assess changes in the mesozooplankton size structure and the composition of the taxa throughout the entire community. Oceanographic conditions changed over the decade: the water column became less stratified, more saline, and colder; the mixed layer deepened; and the oxygen minimum zone became shallower during the second half of the time series (2008–2012) in comparison with the first period (2002–2007). Both the size structure and composition of the zooplankton were significantly associated with oceanographic changes. Taxonomic and size diversity of the zooplankton community increased to the more recent period. For the second period, small sized copepods ( 1.5 mm) and medium size copepods (1–1.5 mm), whereas euphausiids, decapod larvae, appendicularian and ostracods increased their abundance during the second period. These findings indicated that the zooplankton community structure in this eastern boundary ecosystem was strongly influenced by variability of the upwelling process. Thus, climate-induced forcing of upwelling trends can alter the zooplankton community in this highly productive region with potential consequences for the ecosystem food web.

We describe Calicotyle hydrolagi n. sp. (Monogenea: Monocotylidae) infecting the cloaca of deep-water Eastern Pacific black ghost sharks, Hydrolagus melanophasma captured as bycatch at a local fishery for Patagonian toothfish Dissostichus eleginoides, (Nototheniidae) in the Atacama Trench using morphological and nucleotide (LSU rRNA and SSU rRNA) data. This new species is differentiated from its congeners by a number of characters, including the absence of a cecal diverticula, the size and shape of the male copulatory organ and the shape of the vagina, as well as by differences in molecular data (SSU rRNA and LSU rRNA). The suitability of some sclerotized structures such as the male copulatory organ (MCO) as a taxonomic character is discussed; specifically, we found that the relationship between MCO and total length exhibit different trends in members of Calicotyle isolated from sharks, skates and chimaeras. Additional efforts to obtain sample of Calicotyle species and further molecular studies based on ribosomal and mitochondrial genes are necessary to clarify the degree of host specificity in this genus. Additionally, this is the first report of a member of Calicotyle to be reported in the Southeastern Pacific Ocean.

Motivation The BioTIME database contains raw data on species identities and abundances in ecological assemblages through time. These data enable users to calculate temporal trends in biodiversity within and amongst assemblages using a broad range of metrics. BioTIME is being developed as a community-led open-source database of biodiversity time series. Our goal is to accelerate and facilitate quantitative analysis of temporal patterns of biodiversity in the Anthropocene. Main types of variables included The database contains 8,777,413 species abundance records, from assemblages consistently sampled for a minimum of 2 years, which need not necessarily be consecutive. In addition, the database contains metadata relating to sampling methodology and contextual information about each record. Spatial location and grain BioTIME is a global database of 547,161 unique sampling locations spanning the marine, freshwater and terrestrial realms. Grain size varies across datasets from 0.0000000158 km2 (158 cm2) to 100 km2 (1,000,000,000,000 cm2). Time period and grain BioTIME records span from 1874 to 2016. The minimal temporal grain across all datasets in BioTIME is a year. Major taxa and level of measurement BioTIME includes data from 44,440 species across the plant and animal kingdoms, ranging from plants, plankton and terrestrial invertebrates to small and large vertebrates. Software format .csv and .SQL., Global Ecology and Biogeography, 27 (7), ISSN:1466-822X, ISSN:1466-8238

Zooplankton is an important component to understand oceanographic dynamics, they are considered good indicators of environmental variability, since most species are short-lived they can be tight coupling of climate and population dynamics, and some taxa are sensitive to variables such as temperature, quality and quantity of food, oxygenation and stratification. In the Colombian Caribbean two oceanographic cruises were carried out, in order to characterize and analyze the biodiversity of the continental margin, for the periods May-June 2008 and November-December 2009. The objective of this study was to determine which oceanographic variable was the most important in the distribution of zooplankton in the oceanic waters, and how the variables structure the community. In each cruise, zooplankton samples were obtained by vertical hauls with a 1 m2 diameter conical net (200 μm mesh size). The zooplankton community structure was studied by automated image analysis (ZooImage), which combined with abundance data, allowed to calculate the slope of size spectrum, and diversity indexes of taxa and sizes. The environmental variables included temperature, salinity, oxygen and chlorophyll a of the water column, and were used to calculate the stratification with the Brunt-Vaiisala frequency; this information was complemented by satellite images of temperature, surface chlorophyll, geostrophic currents and sea level, obtained from MODIS and AQUA products. The association between environmental variables and the zooplankton community structure was determined using Spearman’s correlation ranges with the Bioenv routine and a stepwise regression model, and Principal component analysis (PCA). Our results showed spatial and temporal patterns in the oceanographic conditions of the study area, such as upwelling in the Northeast region, strong stratification in the Southwest, and mesoscale activity. The abundance of zooplankton exhibited differences between the two climatic seasons and zones. Temporal differences were also evident in the size and diversity of taxa (ANOVA 2-way p

Zooplankton play a key role in the regeneration of nitrogen and phosphorus in the ocean through grazing and metabolism. This study investigates the role of the organic and inorganic nitrogen and phosphorus compounds released by copepods on biogeochemical processes and on the microbial community composition during the OUTPACE cruise (18 February–3 April 2015) at three long duration stations (LD). Two LD stations were located in the Melanesian Archipelago region (MA; LD A and LD B) and one in the South Pacific Gyre (SG; LD C), which represent oligotrophic and ultraoligotrophic regions respectively. At each station, microcosm onboard experiments were performed with locally sampled organisms, comprising a mix of epipelagic copepods fed with their natural food and then incubated along with wild microbial assemblages. In presence of copepods, ammonium and dissolved organic nitrogen showed a significant increase, compared to a control in two situations: in ammonium concentration (increasing rate: 0.29 μmol L−1 h−1 after 4 h of incubation) in LD C and in dissolved organic nitrogen concentration (rate: 2.13 μmol L−1 h−1 after 0.5 h of incubation) in LD A. In addition, during the three experiments, an enhanced remineralization (ammonification and nitrification) was observed when adding copepods compared to the controls. A shift in the composition of active bacterial community was observed for the experiments in LD A and LD B mainly characterized by an increase in Alteromonadales and SAR11, respectively and linked with changes in nutrient concentrations. In the experiment performed in LD C, both groups increased but at different periods of incubation, Alteromonadales between 1 and 2 h after the beginning of the experiment, and SAR 11 at the end of incubation. Finally, our experimental results in near in situ conditions, show that copepods can be a source of organic and inorganic compounds for bacterial communities, which respond to excretion pulses at different scales, depending on the initial environmental conditions and on their community composition. These processes can contribute significantly to nutrient recycling in the epipelagic ecosystem of ultra and oligotrophic oceanic regions.

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 O2 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. chilensis 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.

Copepods are major components of zooplankton in the Humboldt Current system. Here, intra-seasonal (monthly) variation of upwelling and its influence on the copepod community were assessed. Species abundances, species richness, diversity (Shannon–Wiener index) and dominance, were studied during four upwelling periods (2002–2009) at the Station 18 time series off of Concepcion (36°S). Although 77 species were identified, most variability of the community structure was explained by few (

Mesoscale eddies are prominent structures in the world's oceans generating a high degree of spatial and temporal heterogeneity that influences zooplankton distribution. Euphausiids (krill) are a key zooplankton group mainly inhabiting coastal upwelling areas where high productivity, advection, and eddy kinetic energy (EKE) play pivotal roles in the distribution and structure of zooplankton. We analyzed the spatial distribution of the Humboldt Current krill, Euphausia mucronata, in relation to environmental variability and mesoscale circulation during the 2007 austral spring. Using net-based zooplankton samples, remotely sensed environmental conditions, multivariate analysis, and generalized additive models, we described and tested the effect of oceanographic variability and mesoscale eddies on E. mucronata abundance and biomass. E. mucronata was significantly more abundant in coastal (97%) than oceanic habitats, and more abundant in cyclonic cores (mean: 76 indiv. m−2) than in surrounding waters (mean: 13–29 indiv. m−2). Abundance correlated to current and EKE fields at >10–20 cm s−1 and >50–200 cm2 s−2, respectively, and biomass correlated negatively to sea level anomaly and positively to alongshore winds. Krill abundance and biomass were also strongly coupled to both eddy dynamics and the coastal upwelling regime in spring 2007. Mesoscale eddies may doubly influence the E. mucronata population dynamic by retaining krill within them and, by advection from coastal to oligotrophic regions.

The most studied digenean of marine organisms in Chile is by far Proctoeces humboldti , a parasite of the intestine of the clingfish Sicyases sanguineus and gonad of the keyhole limpet Fissurella spp. (progenetic metacercariae). The mussel Perumytilus purpuratus has been suggested as the first intermediate host for this digenean. In a study examining the parasites of S . sanguineus from central Chile, we found specimens of Proctoeces showing significant morphological differences with P . humboldti . To assist in the resolution of the taxonomic identification of these specimens, as well sporocysts obtained from the mussel P . purpuratus from central and northern Chile, phylogenetic studies using DNA sequences from the SSU rRNA, as well the LSU rRNA and Cox 1 gene were performed. Results showed that the clingfish S . sanguineus is a host for two species of Proctoeces ( P . humboldti and P . syciases n. sp.) along the northern and central Chilean coast, without geographic separation; the mussel P . purpuratus is the first intermediate host for P . syciases n. sp. but not for P . humboldti in central and northern Chile. Fissurellids (Archaeogastropoda) along the Chilean coast harbor only progenetic stages of P . humboldti , but there is no evidence of progenesis for P . syciases . The reinstatement of Proctoeces humboldti is strongly suggested.

Here we present results of direct observations of seawater temperature and salinity over the continental shelf off central-south Chile that shows an unprecedented cooling of the entire water column and an increase in upper layer salinity during 2002 to 2013. We provide evidence that this phenomenon is related to the intensification but mostly to a recent southward displacement of the South Pacific High over the same period, from 2007 on. This in turn has accelerated alongshore, equatorward, subtropical coastal upwelling favorable winds, particularly during winter, injecting colder water from below into the upper water column. Consequently, the environmental conditions on the shelf off central-south Chile shifted from a warmer (fresher) to a cooler (saltier) phase; water column temperature dropped from 11.7 °C (2003–2006) to 11.3 °C (2007–2012) and upper layer salinity rose by 0.25; water column stratification gradually decreased. The biological impacts of such abrupt cooling are apparently already happening in this coastal ecosystem, as recent evidence shows substantial changes in the plankton community and negative trends in zooplankton biomass over the same period.

Estimating growth and production rates of mesozooplankton, and copepods in particular, is important in describingflows of material and energy though pelagic systems. Over the past 30 years, the Moult Rate (MR) method has beenused to estimate juvenile copepod growth rates in 40 papers. Yet the MR method has been shown to have seriousflaws. Herewe re-examine the results from the majorityof published MR method studies and re-estimate growth ratesusing the modified Moult Rate (MMR) method, which ascribes changes in mass to the appropriate time period overwhich it was accrued. The MR method has typically over-estimated growth rates (on 80% of occasions) for life stageswhere the subsequent stage is actively moulting; the median and mean MRvalues are 138 and 164%, respectively, ofthe corrected MMR values. We were unable to correct the original data for life stages that are followed by a non-moulting stage, e.g. copepodite stage 5 to adult. We performed experiments with Calanus pacificus to estimate growth ofstage C5 using an alternative method. We found that the error size andsignvaried between masstype (i.e. DW, C andN).Recommendationsfor practicalfutureassessmentsofgrowthincopepodsaremade.KEYWORDS: copepod; error; growth; modified Moult Rate