Humboldt Current System Off Research Articles

Temporal variation of the concentration and biochemical composition of seston within the Humboldt Current System off northern Chile (21°S)

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.

Multiscale characterization of spatial relationships among oxycline depth, macrozooplankton, and forage fish off Peru using geostatistics, principal coordinates of neighbour matrices (PCNMs), and wavelets

Upwelling ecosystems are particularly heterogeneous and present intense mesoscale (tens of kilometres) and submesoscale (hundreds of metres to kilometres) activity that are expected to drive the distribution of the organisms and thus their interactions. Here we addressed the impact of the physical forcing in the northern Humboldt Current system off Peru, which is characterized by the presence of an intense and shallow oxygen minimum zone and used the variability of the depth of the oxycline as a proxy of the physical forcing that impacts the epipelagic communities. We analyzed simultaneous high-resolution acoustic observations of the oxycline depth, the biomass in macrozooplankton, and the biomass in pelagic fish. Three complementary methodologies were considered: (i) geostatistical methods and correlation tests, (ii) principal coordinates of neighbour matrices, and (iii) wavelet analysis. Our results highlight the relevance of a multimethod framework to characterize the multiscale relationships between marine ecosystem components. We also provided evidence that the submesoscale-to-mesoscale variability of the oxycline depth drives the distribution of macrozooplankton, which further structures the distribution of forage fish in a bottom-up cascade.

Concentration of ascorbic acid and innate immune effectors in Engraulis ringens and Strangomera bentincki during their main spawning period (2007–2008) in the Humboldt current system off Chile

In this study, we determined variations in ascorbic acid (AA) concentrations in the gonads and liver, and of the innate immune response (lysozyme activity and antiprotease) in the plasma of Engraulis ringens (anchoveta) and Strangomera bentincki (common sardine) during their reproductive seasons of 2007 and 2008 in the central area of the Humboldt Current. During the main spawning season in 2007, colder environmental conditions, higher phytoplankton biomasses, low dinoflagellate abundance and the dominance of large copepods in winter-early spring and of small copepods in late spring contributed to explain higher AA concentrations in anchoveta tissues. During the warmer year of 2008, lower phytoplankton biomasses, a notable increase of dinoflagellate abundance and the dominance of small-size copepods in winter and of larger copepods in spring occurred along with a drastic drop in AA concentrations in anchoveta tissues. These results contrasted with those in common sardine, a species in which AA did not vary as much as in anchoveta. An inverse trend between AA concentration in the liver and the gonadosomatic index suggested the AA utilization during gonadic maturation. Innate immune parameters were determined for the first time in small pelagic fish and constitute a new baseline data to evaluate their natural response to environmental changes. Changes in the distribution and abundance of edible taxa containing AA and edible for fish along with variations in AA in fish tissues during their reproductive season could become good indicators of the overall fish physiological condition resulting from variations in the trophic web structure.

The role of fungi in processing marine organic matter in the upwelling ecosystem off Chile

In a study that spanned from March 2007 through November 2009, we report high fungal biomass and over 90% of extracellular enzymatic activity occurring in the size classes dominated by fungi during periods of high autotrophic biomass in surface waters of the upwelling ecosystem off central-southern Chile (36°30.80′S–73°07.70′W). Fungal biomass in the water column was determined by the abundance of hyphae and was positively correlated with the concentration of the fungal biomarker 18:2ω6. High fungal biomass during active upwelling periods was comparable to that of prokaryotes (bacteria plus archaea) and was associated with an increase in phytoplankton biomass and in extracellular enzymatic hydrolysis in waters from the depth of maximum fluorescence. We show fungi as a new microbial component in the coastal upwelling ecosystem of the Humboldt Current System off central Chile. Our results suggest that the temporal pattern in fungal biomass in the water column during a year cycle is a reflection of their capacity to hydrolyze organic polymers and, in consequence, fungal biomass and activity respond to a seasonal cycle of upwelling in this ecosystem.

Recurrent, thermally-induced shifts in species distribution range in the Humboldt current upwelling system

El Niño-Southern Oscillation (ENSO) is a global climate variablility, which fundamentally influences environmental patterns of the Humboldt Current System (HCS) off Chile and Peru. The surf clams Donax obesulus and Mesodesma donacium are dominant and highly productive bivalves of exposed sandy beaches of the HCS. Existing knowledge indicates that El Niño (EN, warm phase of ENSO) and La Niña (LN, cold phase of ENSO) affect populations of both species in a different way, although understanding of the mechanisms underlying these effects is still lacking. The aim of this study was to test hypotheses attempting to explain field observations on the effect of strong EN or LN events by using controlled experimental conditions. Growth and mortality rates of both species were registered during a four-week experiment under EN temperature conditions, normal temperature conditions and LN temperature conditions. While D. obesulus exhibited reduced growth and higher mortality under LN conditions, M. donacium showed reduced growth and higher mortality under EN conditions. The results clearly indicate different temperature tolerance windows for each species, possibly reflecting the evolutionary origins of the Donacidae and Mesodesmatidae in regions with contrasting temperature regimes. These results provide experimental support for previous hypotheses suggesting that thermal tolerance is the driving factor behind observed changes in the species distributions of D. obesulus and M. donacium during the extreme phases of ENSO.

Diet of sardine ( Sardinops sagax) in the northern Humboldt Current system and comparison with the diets of clupeoids in this and other eastern boundary upwelling systems

Sardines are one of the main small pelagic fish resources in eastern boundary upwelling systems (EBUS) where they play an important ecological role both as a predator of plankton and as prey of top predators. Sardine trophodynamics have been relatively well studied in three of the EBUS (the Benguela, California and Canary upwelling systems) but not in the Humboldt Current system. In this paper we describe the diet of sardine Sardinops sagax in the northern Humboldt Current system (NHCS) off Peru, using an analytical method which assesses relative dietary importance in terms of estimated prey carbon content. We assessed sardine diet by examining a total of 555 stomachs collected during six surveys conducted off Peru during the period 1996–1998, and compare our results with the diet of anchoveta Engraulis ringens off Peru and with the diets of sardines from the southern Benguela (also S. sagax) and the northern Canary ( Sardina pilchardus) upwelling systems. The diet of sardine off Peru is based primarily on zooplankton, similar to that observed for anchoveta but with several important differences. Firstly, sardine feed on smaller zooplankton than do anchoveta, with sardine diet consisting of smaller copepods and fewer euphausiids than anchoveta diet. Secondly, whilst phytoplankton represents <2% of sardine dietary carbon, this fraction is dominated by dinoflagellates, whereas diatoms are the dominant phytoplankton consumed by anchoveta. Hence, trophic competition between sardine and anchovy in the northern Humboldt Current system is minimized by their partitioning of the zooplankton food resource based on prey size, as has been reported in other systems. Whereas sardine in the NHCS feed on smaller zooplankton than do anchovy in that system, sardine in the NHCS forage on larger prey and obtain a substantial portion of their dietary carbon from euphausiids compared to sardine from the northern Canary and southern Benguela Current systems.

Small pelagic fish reproductive strategies in upwelling systems: A natal homing evolutionary model to study environmental constraints

Although little is known about the individual-level mechanisms that influence small pelagic fish species’ reproductive strategy, Mullon et al. [Mullon, C., Cury, P., Penven, P., 2002. Evolutionary individual-based model for the recruitment of anchovy ( Engraulis capensis) in the southern Benguela. Canadian Journal of Fisheries and Aquatic Sciences 59, 910–922] showed that the observed anchovy spawning patterns in the southern Benguela Current system off South Africa could be accurately reproduced by simulating a natal homing reproductive strategy, i.e. individuals spawning at their natal date and place. Here we used a similar method, i.e., an individual-based model of the natal homing reproductive strategy, and applied it to other upwelling systems: the northern Humboldt Current system off Peru, the southern Humboldt Current system off Chile and the central Canary Current system off Morocco. We investigated the spatial (horizontal and vertical) and seasonal spawning patterns that emerged after applying different environmental constraints in the model, and compared these to observed spawning patterns of sardine and anchovy in their respective systems. The selective environmental constraints tested were: (1) lethal temperature; (2) retention over the continental shelf; and (3) avoidance of dispersive structures. Simulated horizontal spatial patterns and seasonal patterns compared reasonably well with field data, but vertical patterns in most cases did not. Similarly to what was found for the southern Benguela, temperature was a determinant constraint in the southern Humboldt. The shelf retention constraint led to selection of a particular spawning season during the period of minimum upwelling in all three of the upwelling regions considered, and to spatial patterns that matched observed anchovy spawning off Chile and sardine spawning off Morocco. The third constraint, avoidance of dispersive structures, led to the emergence of a spawning season during the period of maximum upwelling off Chile and Morocco, but not in Peru. The most accurate representation of observed spatio-temporal spawning patterns off Peru was achieved through a combination of shelf retention and non-dispersion constraints.

Carbon fluxes within the epipelagic zone of the Humboldt Current System off Chile: The significance of euphausiids and diatoms as key functional groups for the biological pump

The information from 54 drifting sediment traps deployed between 1997 and 2006 along the Humboldt Current System off Chile (from 19.9°S to 42.2°S) was analyzed to contribute to unveiling the recurrent global-ocean issue of the lack of relationship between gross primary production (GPP) and particulate organic carbon (POC) export below 50 m depth. When the proportion of carbon that effectively sinks is relatively low compared to the carbon being fixed through GPP, a significant amount (average of 32%) of the sinking organic matter is composed of diatoms, regardless of GPP rates. Such a fraction seems to be affected by the physiological state of phytoplankton. In contrast, when the fraction of carbon sinking is high relative to GPP, most of sinking organic matter is composed of euphausid faecal strings. Such a situation occurs at relatively low values of GPP and chlorophyll-a. Most of these high sinking rates of pellets and low phytoplankton biomass occur during summer, when physical conditions favour the presence of phytoplankton blooms, and when the GPP/Biomass ratio indicates healthy phytoplankton physiological conditions. All this evidence supports the assessment of the relevance of euphausiids as key species in the Humboldt Current System pointing to (i) the top–down control that euphausiids are capable of exerting over primary producer biomass, and (ii) euphausiids‘ paramount role on total organic carbon flux over the Concepción continental shelf, regarding both POC export to the sediments and possibly the channelling of GPP directly to higher trophic levels.

Water column distribution of phospholipid-derived fatty acids of marine microorganisms in the Humboldt Current system off northern Chile

Suspended particulate matter samples from the oxygenated surface zone, the oxygen minimum zone, and the oxygenated deeper zone were collected from the upwelling area off Antofagasta in northern Chile during austral autumn (April 2001) to study the composition of microbial phospholipid-derived fatty acid methyl esters, using capillary gas chromatography-mass spectrometry. Whereas phytoplanktonic carbon dominated living organic matter near the coast, bacterial carbon was most abundant offshore. The biomarker distribution showed some differences between the depth levels sampled, such as the highest microbial abundance in the epipelagic zone represented by phytoplankton, especially diatoms, and a homogeneous distribution of bacterial biomarkers, with no indication of vertical segregation of functional groups as previously thought.

Common catabolic enzyme patterns in a microplankton community of the Humboldt Current System off northern and central-south Chile: Malate dehydrogenase activity as an index of water-column metabolism in an oxygen minimum zone

Abstract An extensive subsurface oxygen minimum zone off northern and central-south Chile, associated with the Peru–Chile undercurrent, has important effects on the metabolism of the organisms inhabiting therein. Planktonic species deal with the hypoxic and anoxic environments by relying on biochemical as well as physiological processes related to their anaerobic metabolisms. Here we characterize, for the first time, the potential enzymatic activities involved in the aerobic and anaerobic energy production pathways of microplanktonic organisms (

Spatial and temporal variability of planktonic archaeal abundance in the Humboldt Current System off Chile

Abstract The latest advances in the field of microbial ecology have shown that planktonic Archaea are one of the most abundant unicellular microorganisms of the oceans. However, no information is available on the contribution this group makes to the prokaryote assemblages that inhabit the eastern South Pacific Ocean. Here, we describe the relative abundance and vertical distribution of planktonic Archaea off northern and central-southern Chile. Data come from several cruises and a 45-month time series at a station located on the shelf off central-southern Chile. Both the taxonomic composition of the prokaryote community and its relative abundance were determined using quantitative dot blot 16S-rRNA hybridizations. Total Archaea in central-southern Chile made up 6–87% of the prokaryote rRNA in the water column and did not present evidence of any seasonal pattern. Crenarchaea were the most abundant archaeal group at this site and were significantly associated with the ammonium concentration ( r 2 =0.16, p =0.0003, n =80). Archaeal abundance in the time series was usually greater in the deeper layer (>50 m), with contributions reaching up to ∼90% of the prokaryote rRNA on certain occasions, and decreasing towards the surface. Important increments in the relative abundance of total Archaea were observed on given dates at the surface of the time-series station off central-southern Chile. Off northern Chile, total Archaea normally contributed from ∼10% to 50% of the prokaryote rRNA found between 10 and 1000 m, and were generally important in the mesopelagic realm. Our results indicate that Archaea constitute an important fraction of the prokaryote assemblage in the water column of the Humboldt Current System, especially in the oxygen minimum zone.

Reproduction and feeding of Sagitta enflata in the Humboldt Current system off Chile

Abstract Giesecke, R., and González, H. E. 2008. Reproduction and feeding of Sagitta enflata in the Humboldt Current system off Chile. – ICES Journal of Marine Science, 65: 361–370. This study is based on 3 years (August 2002–July 2005) of monthly zooplankton sampling at a fixed station located 18 km off Coliumo Bay (36°S), Chile. The reproduction of Sagitta enflata, its feeding rate, specific daily ration, and prey selectivity were analysed and related to several environmental variables: temperature, salinity, dissolved oxygen, chlorophyll a concentrations, and both meso- and micro-zooplankton abundance. The main predatory activity of S. enflata was centred on the copepods Paracalanus parvus, Oithona spp., and Calanus chilensis. These three species were consumed at different rates, depending mainly on the maturity of the S. enflata population. When Stages I and II individuals dominated, predation focused on the small P. parvus and Oithona spp., whereas more mature populations (Stages III and IV) preyed selectively on C. chilensis. The mean specific daily ration of 0.1 d−1 increased to 0.5 d−1 before and during maturation. The reproductive phase of S. enflata was closely coupled with the abundance of nauplii, suggesting that chaetognath reproduction paralleled that of copepods, most likely to diminish the mortality of its offspring resulting from starvation. The relationships between these were included in a conceptual model and their ecological significance is discussed.

Carbon fluxes within the pelagic food web in the coastal area off Antofagasta (23°S), Chile: The significance of the microbial versus classical food webs

Trophic interactions and the relevance of the “classical” (CFW) versus the “microbial” (MFW) food webs were studied in the upwelling system of Antofagasta (23°S), northern Humboldt Current System (HCS) off Chile. Biological and ecological data gathered from the study area during 1996 and 1999–2002 and complementary data from the literature were analysed using the Ecopath with Ecosim software version 5.0 (EwE). The model includes the following functional groups: Detritus, dissolved organic matter (DOM), bacteria, phytoplankton, appendicularians, salps, calanoid copepods, cyclopoid copepods, chaetognaths, ctenophores, clupeiform fishes. The Antofagasta's model indicate that only 18% of the total trophic relationships up to clupeiforms include only organisms of the CFW, while it is increased up to 82% when trophic relationships with organisms of the MFW are included. Removing the MFW from a complex, multi-level, trophic pathways, the energy transfer efficiency that characterise the study area either decreased or increased their value from detritus (from 14.4% to 13.6%) and primary production (from 11.0% to 15.1%), respectively. The total net primary production (PP) of the system with and without the MFW is similar (2.3 grC m −2 d −1 and 2.2 grC m −2 d −1), however, the total energy throughput increased in a system with MFW from ∼4.7 grC m −2 d −1 to ∼9.8 grC m −2 d −1. Thus, although the energy transfer efficiency is higher in a system without the MFW, the total system throughput is two times higher when it is considered. This might be due to (1) the inclusion of large new compartments in different trophic levels (such as DOM, bacteria), (2) the inclusion of the MFW would enhance the recycling of materials and energy and (3) the inclusion of new pathways such as bacteria – appendicularians/salps – anchovy (clupeiforms), that might produce a close link between the base of the microbial loop and clupeiforms, bypassing most of the MFW. The exclusion of the microbial loop from trophic models should strongly affect different planktonic groups such as salps, small cyclopoid copepods and appendicularians because they feed mainly (or partially, such as euphausiids) on small-size particles such as bacteria, microflagellates and ciliates. Thus, both CFW and MFW constitute highly complementary and interconnected trophic pathways from microbes up to fishes, and where more resolution at lower trophic level would be required to derive sensible model results that satisfactorily represent the system behaviour (i.e. ecosystem approach).

The relative importance of microbial and classical food webs in a highly productive coastal upwelling area

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 &gt;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.

Relationship between viral and prokaryotic abundance on the Bajo O’Higgins 1 Seamount (Humboldt Current System off Chile)

There is little known about the ecology of microbial communities living in the water column over seamounts. Here, for the first time, the spatial distribution and abundance of virus-like particles (VLP) are described over a seamount. The association between VLP distribution, prokaryotic abundance, and environmental variables is also analyzed. Sampling was conducted in December 2004 on the Bajo O’Higgins 1 seamount (32°54’S, 73°53’W) located in the Humboldt Current System off Chile. A oxygen minimum layer (OMZ) was clearly present between 130 and 280 m in the water column over the seamount. Water samples were taken with Niskin bottles at 10 oceanographic stations over the seamount at depths of 5, 20, 50, 75, 100, and 150 m and at the benthic boundary layer (BBL; 5-12 m over the sediments). Temperature, salinity, oxygen, chlorophyll , and phaeopigments were measured at each station. Viral and prokaryotic abundances were determined with fluorochrome SYBR Green I. Viral abundance ranged from 1.53 x 10 9 VLP L -1 - 16.48 x 10 9 VLP L -1 , whereas prokaryotic abundance ranged from 1.78 x 10 8 cell L -1 - 14.91 x 10 8 cell L -1 . The virus-like particle/prokaryote ratio varied widely among the analyzed layers (i.e. surface, OMZ, and BBL), probably due to the presence of different prokaryotic and viral assemblages in each layer. Our results indicate that the environmental conditions, mainly the concentration of dissolved oxygen in the water column over Bajo O’Higgins 1 seamount, shape the association between viral and prokaryotic abundance.

Solar UV radiation modulates daily production and DNA damage of marine bacterioplankton from a productive upwelling zone (36°S), Chile

In upwelling ecosystems, such as the Humboldt Current system (HCS) off Concepción, the effects of solar radiation on bacterioplankton incorporation rates have been related to previous light acclimation and responses to irradiance. In this paper, we study the daily effect of Photosynthetic Active Radiation (PAR, 400–700 nm) and ultraviolet radiation UVR (280–400 nm) on bacterial secondary production (BSP). We also considered the DNA damage–repair response to solar radiation stress by the induction of cyclobutane pyrimidine dimers (CPDs). Experiments were conducted with natural bacterioplankton assemblages (0.2–0.7 μm) collected off Concepción (36°S), during the austral Spring, October–November, 2004. Surface (0.5 m) and subsurface (80 m) bacterioplankton samples were exposed to different solar radiation treatments for 5–20 h. BSP was estimated by 14C-leucine and 3H-thymidine incorporation at several time intervals, whereas CPDs accumulation was assessed using immunoassay techniques. During high irradiance periods, BSP was mainly affected by PAR in both surface and subsurface assemblages and, to a lesser, but significant (Tukey < 0.05) extent, by UV-A (320–400 nm) and UV-B (280–320 nm) radiation. Maximum inhibition of BSP in surface waters was 78%; growth rates ( μ) and bacterial growth efficiency (BGE) were also low (78% and 66% respectively). Subsurface water assemblages, on the contrary, showed a ∼ 25 fold enhancement of BSP, μ, and BGE. Both types of assemblages had a rapid CPDs accumulation (maximum 60 CPDs Mb − 1 ) during high irradiance periods. Recovery of BSP inhibition and DNA damage in surface bacteria was total after sunset and after the night incubation period, resembling pre-exposure levels. Despite subsurface BSP enhancement during day–night exposure, residual DNA damage was detected at the end of the experiment (20 CPDs Mb − 1 ) suggesting a chronic DNA damage. Our results represent the worst case scenario (i.e., assemblages receiving surface irradiances as may occur in this upwelling zone) and indicate that surface and subsurface bacterial assemblages in the HCS are both highly sensitive to solar irradiance. However, they showed different responses, with surface bacteria having more effective photorepair mechanisms, and sustaining higher BSP than subsurface assemblages.

Simulating the dynamics of the Humboldt Current system off Peru with a nonlinear terrain-following coordinate model

As estruturas térmicas superficial e vertical, e a circulação oceânica do sudeste do Pacífico tropical (4o S-26o S / 70o W-91o W) são aqui analisadas. Trata-se da região onde parte da Sub-Corrente do Peru-Chile se desenvolve, influenciando sobre a distribuição dos componentes bióticos e abióticos ao longo da costa do Peru, e contribuindo para a variabilidade climática sobre o continente Sul Americano. O sistema de modelagem oceânica regional (ROMS) é então utilizado para simular o ciclo sazonal da circulação oceânica com o emprego de uma malha horizontal anisotrópica (1/2o -1/6o ) e 20 camadas verticais ajustadas à topografia variável. Através desta resolução foi possível ilustrar a complexidade dos fenômenos de meso-escala que ocorrem na região. A estrutura térmica superficial simulada correspondeu às observações de satélite, e confirmaram a presença de águas oceânicas mais quentes (e mais salinas) adjacentes à costa do Peru em Janeiro, em comparação ao mês de Julho, quando águas mais frias (e menos salinas) são observadas. Os resultados numéricos também reproduziram satisfatoriamente a evolução espaço-temporal das correntes de fronteira leste, bem como os mecanismos de ressurgências nas regiões costeiras de Paita e Callao. Futuros esforços de modelagem matemática desta região serão direcionados à aplicação de malhas de alta resolução acopladas (1/12o , 1/16o ), com a consideração de rotinas biogeoquímicas e ecológicas acopladas aos processos físicos. Palavras-Chave: Pacífico tropical Leste, Temperatura de superfície, Dados de satélite, Ressurgência costeira, ROMS.

Biomass size-spectra of macrobenthic communities in the oxygen minimum zone off Chile

Estimates of macrofaunal secondary production and normalized biomass size-spectra (NBSS) were constructed for macrobenthic communities associated with the oxygen minimum zone (OMZ) in four areas of the continental margin off Chile. The presence of low oxygen conditions in the Humboldt Current System (HCS) off Chile was shown to have important effects on the size structure and secondary production of the benthic communities living in this ecosystem. The distribution of normalized biomass by size was linear (log 2–log 2 scale) at all stations. The slope of the NBSS ranged from −0.481 to −0.908. There were significant differences between the slopes of the NBS-spectra from the stations located in the OMZ (slope = −0.837) and those located outside the OMZ (slope = −0.463) ( p < 0.05). The results of this study suggest that low oxygen conditions (<0.5 ml L −1) appear to influence biomass size-spectra, because small organisms are better able to satisfy their metabolic demands. The annual secondary production was higher off central Chile (6.8 g C m −2 y −1) than off northern Chile (2.02 g C m −2 y −1) and off southern Chile (0.83 g C m −2 y −1). A comparison with other studies suggests that secondary production in terms of carbon equivalents was higher than in other upwelling regions.

Seasonal and interannual variability in the flux of planktic foraminifera in the Humboldt Current System off central Chile (30°S)

Abstract Seasonal and interannual changes in the flux of planktic foraminifers were studied in the Humboldt Current System off Coquimbo, Chile (30°S; 73°15′W), using material collected by time series sediment traps located at 2300 m water depth and 100 nautical miles from the coast. The almost continuous record spans 6 years (1993–1998) with a temporal resolution of 6–13 days. The seasonal flux pattern of planktic foraminifers was marked by high fluxes during austral late winter–early summer (August–January) and low fluxes during the fall–early winter period (March–July). Five species contributed ∼90% of the total flux of planktic foraminifers: Globigerina bulloides , Neogloboquadrina incompta , N. pachyderma , N. dutertrei , and Globigerinella calida . Stable oxygen isotope variability in foraminifer shells appears to be driven by seasonal changes in surface seawater temperature; isotope data of G. bulloides and N. incompta (>212 and 150–212 μm size classes) suggest that water-column stratification dominates during the low-flux period and mixing during the high-flux period. The strong 1997–1998 El Nino event had only a limited impact on the planktic foraminifer flux. The most significant El Nino-related signal was a remarkable increase in the flux and abundance of species that, under normal conditions, only accounted for

Biological and chemical consequences of the 1997–1998 El Niño in the Chilean coastal upwelling system: a synthesis

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 Nino (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 Nino-La Nina 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 400,000 tons 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.