Carmen E. Morales

Interannual variability in the mesoscale distribution of the depth of the upper boundary of the oxygen minimum layer off northern Chile (18–24S): Implications for the pelagic system and biogeochemical cycling

The low oxygen concentration (<2 ml L -1 ) at relatively shallow depths (<100 m) in the coastal upwelling zone and in the adjacent oceanic area is a distinct feature of the eastern boundary Humboldt Current System (HCS) off Peru and northern Chile; it affects the distribution of pelagic organisms and is associated with an important denitrification regime in the water column. Nevertheless, little information is available about the spatial and temporal variability in the distribution of the Oxygen Minimum Layer (OML) present in the HCS and the impact of its variability upon the pelagic system and biogeochemical cycles in the region. The present study reviews the oceanographic data obtained for the area off northern Chile (ca. 18 to 24S, out to 370 km), between 1980 and 1997, with the aim of characterizing the depth distribution of the upper boundary of the OML (1 ml L -1 iso-oxyline, representing also the oxycline) and investigating the association of its interannual variability with changes in coastal sea level and in the equatorial and local thermoclines. The depth of the upper boundary of the OML undergoes pronounced deepening during the occurrence of warm ENSO (El Nino Southern Oscillation) events over the whole area of study, and this, in turn, determines a condition of higher oxygen concentrations in the top 100 m layer. These changes follow closely the patterns of interannual variability in coastal sea level and depth of the thermocline in the area of study during the 1980-1997 period. Most of this variability can be accounted for, as expected from previous studies, by remote forcing originating in the equatorial zone of the Pacific Ocean, as evidenced from the significant correlation between the above local parameters and the interannual variability in the depth of the equatorial thermocline. The 1982-83 and 1997-98 El Nino events seemed to have been the most important ones in terms of their effects upon sea level and depth of the thermocline and oxycline off northern Chile. The potential impacts of the interannual changes in the depth of the upper boundary of the OML upon the pelagic system and biogeochemical cycling in the region are discussed.

New regulations in Chilean fisheries and aquaculture : ITQ's and Territorial Users Rights

Abstract The large industrial fishery development that turn Chile into the third fishing nation in the world is described, and recent regulatory innovations introduced by new Fishery and Aquaculture legislation are reviewed. In addition to classical Fishery management tools, different types of limited entry systems are now defined in the law and applicable to Chilean fisherie. These for the first time include allocation of resources in the form of Individual Fishing Quotas and Individual Transferable Quotas (IFQs and ITQs). Territorial User’s Rights in Fisheries (TURF’s) were incorporated in the law to enhance self-regulatory practices among artisanal fishermen. Among them, the Areas for Management and Exploitation for Benthic Resources (AME) represent an associative assignment of TURFs. Large-scale zoning is used to re-define Aquaculture Grants and to ritualise the conflicts between Artisanal and Industrial fishermen by establishing the Artisanal Reserve in which small-scale coastal fishermen have Priority Access. Performance of the new management instruments are documented with case studies, for the following fisheries: the loco ( Concholepas concholepas ) a carnivorous snail, keyhole limpets (Fissurella spp.), langostino or squat lobster ( Cervimunida johni ), Black hake ( Dissostichus eleginoides ) and the Yellow prawn ( Pleuroncodes monodon ).

Chlorophyll- a distribution and mesoscale physical processes in upwelling and adjacent oceanic zones off northern Chile (summer–autumn 1994)

(HumboldtCurrent System), during the austral summer (February-March) and autumn (May) of 1994, were studied in the region bounded by 18-24`S and 70-72°W (out to 200 km from the coast ; 0-100 in depth) ; within this region, nutrients were measured in an area of persistent coastal upwelling (^-19-22`S, out to 80 km from the coast) . Temperature and salinity distributions, as well as nutrient concentrations, indicated the occurrence of active upwelling during both cruises . Also, and together with maps of geopotential anomaly (0/200 dbar) and depth of the thermocline (15°C isotherm), their distribution suggested the presence of a mainly equatorward flow, anticyclonic eddy-like structures, and intrusions of warm (>19 -C).high salinity (> 35 .0 psu), subtropical water towards the coast . A tongue of cooler and lower salinity water, and of lower flow fields, extended from the coast towards the offshore zone during both sampling periods, in association with higher chl-a concentrations (> 1 mg m -3, > 20 mg m -2 between 0 and 25 in depth) and predominance of netphytoplankton (> 20µm) . The comparison of these results with those for the winter and spring of 1993 in the same area suggest a relatively weak seasonal signal in chl-a concentration during the 1993-1994 period, with higher water column concentrations during the summer and spring periods in the selected upwelling area, though surface chl-a concentrations for the whole of the area did not vary significantly .

Diet selection of the Chilean stone crab Homalaspis plana

AbstractDiet selection of the Chilean stone crab Homolaspis plana (Milne-Edwards, 1834) was studied using the optimal foraging theory to explain its feeding strategy. The hypothesis that H. plana prefers prey species of the highest prey (“energy”) value was experimentally tested on adult crabs during 1980–1981. Food value was defined as the ratio between caloric content and consumption time, according to energy maximization as the criterion to optimize diet selection. Diet composition of adult crabs from the littoral of Valparaíso (Chile) and ingestion under laboratory conditions were studied to determine type, size and quantity of food to be offered in experiments on prey-type preference. Porcellanid crabs, barnacles and bivalves were the most frequently occurring items in stomachs from in situ conditions. In the aquaria, daily ingestion rates were quite variable among crabs and among days. H. plana showed no size preference for molluscs (Tegula atra, Semimytilus algosus) but preferred larger sizes of porcellanids. The order of preference for prey type was S. algosus>T. atra> porcellanids. However, no differences between their energy values were found and, therefore, the optimal foraging hypothesis was rejected. By extension, the energy maximization criterion alone may not explain the diet selection of H. plana under experimental conditions.

Phytoplankton phenology in the coastal upwelling region off central-southern Chile (35°S–38°S): Time-space variability, coupling to environmental factors, and sources of uncertainty in the estimates

The annual cycle and phenology of phytoplankton (satellite-derived chlorophyll-a, Chl-a) in the coastal upwelling region off central-southern Chile, their time-space variation, the extent of their coupling with those of wind-driven upwelling (as Zonal Ekman Transport, ZET), Sea Surface Temperature (SST), and Photosynthetically Active Radiation (PAR) were analyzed using a ∼10 year satellite time series (2002–2012). Wavelet analysis (WA) was applied to extract the dominant frequencies of variability and their recurrence, to derive the phenological indexes, and to assess the extent of the coupling between Chl-a and environmental forcing in the annual frequency. Index estimates were obtained from minimum and maximum accumulated values in two different frequency bands, annual (WA-ANF) and all except the synoptic (WA-ALF). The annual frequency was dominant in all the variables; however, the annual cycle and phenology of Chl-a displayed higher submeso and mesoscale variability. The mean onset date of Chl-a was similar to those of PAR and ZET with WA-ALF and cross WA indicated that, for the most part, their annual cycles were coupled or coherent. Few interannual changes in Chl-a phenology were detected, including a ∼1 month longer duration (WA-ALF) during La Nina 2010–2011. The mean anomalies in the magnitudes of Chl-a and ZET during the upwelling season showed a slight but significant trend, negative for Chl-a and positive for ZET, while SST remained relatively constant. This pattern was unexpected since three La Nina-related conditions were identified during the 2007–2012 period.

Time-Space Variability of Chlorophyll-a and Associated Physical Variables within the Region off Central-Southern Chile

Abstract: Time-space fluctuations of chlorophyll-a (Chl-a) within the region off central-southern Chile (33–42°S), and their association with meteorological-oceanographic conditions, were analyzed using satellite time series data (2002–2012). The mean distribution of moderate values of Chl-a (~0.5 mg∙m −3 ) in the northern section (33–38°S) extended out to ~200 km of the coast whereas they were restricted to a narrower band in the southern section (38–42°S). Mean wind stress and wind stress curl were upwelling favorable for most part of the year in the northern section whereas upwelling-downwelling periods were distinct in the southern section. The dominant frequency of Chl-a variability in the coastal zone and the coastal transition zone was annual, as it was for the rest of the variables, except in a transitional band between these zones and where a semi-permanent jet is located. At the annual frequency, the alongshore distribution of coastal Chl-a presented strong discontinuities, with minimum values around upwelling centers (~37 and 40°S) and higher values (> 2 mg∙m

Front-Eddy Influence on Water Column Properties, Phytoplankton Community Structure, and Cross-Shelf Exchange of Diatom Taxa in the Shelf-Slope Area Off Concepción (∼36-37°S)

In eastern boundary current systems (EBCSs), submesoscale to mesocale variability contributes to cross-shore exchanges of water properties, nutrients, and plankton. Data from a short-term summer survey and satellite time series (January-February 2014) were used to characterize submesoscale variability in oceanographic conditions and phytoplankton distribution across the coastal upwelling and coastal transition zones north of Punta Lavapie, and to explore cross-shelf exchanges of diatom taxa. A thermo-haline front (FRN-1) flanked by a mesoscale anticyclonic intrathermocline eddy (ITE-1), or mode-water eddy, persisted during the study period and the survey was undertaken during a wind relaxation event. At the survey time, ITE-1 contributed to an onshore intrusion of warm oceanic waters (southern section) and an offshore advection of cold coastal waters (northern section), with the latter forming a cold, high chlorophyll-a filament. In situ phytoplankton and diatom biomasses were highest at the surface in FRN-1 and at the subsurface in ITE-1, whereas values in the coastal zone were lower and dominated by smaller cells. Diatom species typical of the coastal zone and species dominant in oceanic waters were both found in the FRN-1 and ITE-1 interaction area, suggesting that this mixture was the result of both offshore and onshore advection. Overall, front-eddy interactions in EBCSs could enhance cross-shelf exchanges of coastal and oceanic plankton, as well as sustain phytoplankton growth in the slope area through localized upward injections of nutrients in the frontal zone, combined with ITE-induced advection and vertical nutrient inputs to the surface layer.

An Appraisal of the Stoichiometry of Dissolved Oxygen/Nutrient Inter-Relationships in the Upwelling System Off Northern Chile

Using vertical profile data from the upwelling system off northern Chile, the slopes of dissolved oxygen/nutrient concentration regressions have been analysed, in conjunction with a value of 1·4 for the molar ratio of net community oxygen production to nitrate-driven carbon dioxide assimilation, to investigate the stoichiometric inter-relationships between photosynthetic oxygen production and carbon dioxide and nutrient consumption. There was little interseasonal variation in ΔCO 2 /ΔDIN (nitrate+nitrite) molar ratios, ranging from 10·3 to 11·6 in the near-shore zone of active upwelling and 6·7 to 9·0 in mid-water, between 25 and 50 m depth offshore. Although the former range exceeded the value expected from Redfield-Richards stoichiometry (6·6) by more than 50%, it was in line with published ratios for phytoplankton blooms in coastal and oceanic waters. Mean ΔDIN/ΔPO 4 ratios were similar for the near-shore stations and the mid-water, ranging respectively from 7·0 to 10·7 and 8·4 to 11·5, these subRedfield-Richards values mirroring the ratios of the nutrient concentrations in the water and probably implying ‘luxury’ consumption of phosphate. Seasonal variations in the ΔO 2 /ΔPO 4 ratios for the near-shore zone are shown to be consistent with the view that, in the austral spring and summer when upwelling is strongest in the area, the main source of the water coming to the surface is the Peru-Chile Undercurrent, whereas in the autumn, it could be of subantarctic origin.

Phytoplankton Size Structure in Association with Mesoscale Eddies off Central-Southern Chile: The Satellite Application of a Phytoplankton Size-Class Model

Understanding the influence of mesoscale and submesoscale features on the structure of phytoplankton is a key aspect in the assessment of their influence on marine biogeochemical cycling and cross-shore exchanges of plankton in Eastern Boundary Current Systems (EBCS). In this study, the spatio-temporal evolution of phytoplankton size classes (PSC) in surface waters associated with mesoscale eddies in the EBCS off central-southern Chile was analyzed. Chlorophyll-a (Chl-a) size-fractionated filtration (SFF) data from in situ samplings in coastal and coastal transition waters were used to tune a three-component (micro-, nano-, and pico-phytoplankton) model, which was then applied to total Chl-a satellite data (ESA OC-CCI product) in order to retrieve the Chl-a concentration of each PSC. A sea surface, height-based eddy-tracking algorithm was used to identify and track one cyclonic (sC) and three anticyclonic (ssAC1, ssAC2, sAC) mesoscale eddies between January 2014 and October 2015. Satellite estimates of PSC and in situ SFF Chl-a data were highly correlated (0.64 < r < 0.87), although uncertainty values for the microplankton fraction were moderate to high (50 to 100% depending on the metric used). The largest changes in size structure took place during the early life of eddies (~2 months), and no major differences in PSC between eddy center and periphery were found. The contribution of the microplankton fraction was ~50% (~30%) in sC and ssAC1 (ssAC2 and sAC) eddies when they were located close to the coast, while nanoplankton was dominant (~60–70%) and picoplankton almost constant (<20%) throughout the lifetime of eddies. These results suggest that the three-component model, which has been mostly applied in oceanic waters, is also applicable to highly productive coastal upwelling systems. Additionally, the PSC changes within mesoscale eddies obtained by this satellite approach are in agreement with results on phytoplankton size distribution in mesoscale and submesoscale features in this region, and are most likely triggered by variations in nutrient concentrations and/or ratios during the eddies’ lifetimes.

Coastal Upwelling Front Detection off Central Chile (36.5–37°S) and Spatio-Temporal Variability of Frontal Characteristics

In Eastern Boundary Upwelling Systems, cold coastal waters are separated from offshore by a strong cross-shore Sea Surface Temperature (SST) gradient zone. This upwelling front plays a major role for the coastal ecosystem. This paper proposes a method to automatically identify the front and define its main characteristics (position, width, and intensity) from high resolution data. The spatio-temporal variability of the front characteristics is then analyzed in a region off Central Chile (37°S), from 2003 to 2016. The front is defined on daily 1 km-resolution SST maps by isotherm T0 with T0 computed from mean SST with respect to the distance from the coast. The probability of detecting a front, as well as the front width and intensity are driven by coastal wind conditions and increased over the 2007–2016 period compared to the 2003–2006 period. The front position, highly variable, is related to the coastal jet configuration and does not depend on the atmospheric forcing. This study shows an increase by 14% in the probability of detecting a front and also an intensification by 17% of the cross-front SST difference over the last 14 years. No trend was found in the front position.