Cristian Hakspiel | Universidad Autonoma de Baja California (original) (raw)

Papers by Cristian Hakspiel

Progress in Oceanography, 2022

Multiple publications over the past decades argue that the Gulf of California is a region with hi... more Multiple publications over the past decades argue that the Gulf of California is a region with high biological diversity and productivity. However, ecosystem resilience to climate disturbances and anthropogenic stressors in the Gulf of California remains poorly explored. One method to assess ecosystem resilience based on ecological indicators is the analysis of continuous records of critical environmental variables. Here we analyze satellite time-series of sea surface chlorophyll-a concentration (Chl-a) over the past two decades (1997–2020) and hydrographic data obtained from the central Gulf of California (2005–2019) to detect abrupt transitions (tipping points) and shifts in the temporal trends and their association with the most prominent modes of climate variability in the northeastern Pacific. In addition, based on the critical “slow-down theory”, we estimated the autocorrelation time (AcT) and standard deviation (SD) of satellite sea surface Chl-a, as a resilience indicator (RI), to monitor whether early-warning signals anticipate any impacts of climate change. We observed a clear negative trend in SST in the pre-2012 period, related to decadal and multiannual modes of variability of the Pacific decadal Oscillation (PDO), El Niño Modoki (EMI), and Pacific Meridional Mode (PMMSST). In contrast, a positive SST trend in the period post-2012 to 2017 was associated with the multiannual warming event in the northeastern Pacific that peaked during the intense 2015–2016 El Niño. These trends differentially regulate the Chl-a response during the cold (November to April) and warm (June to October) seasons, in line with the shift of regime in 2012. The critical transition early-warning signal depicted better consistency in the use of increasing SD in Chl-aSat time series, but still, AcT provides an effective predictor of a slowdown in most cases. GAM results showed that the main mode of climate variability that affects Chl-a was PMMSST. EMI, NPGO, and PDO modes had a less significant influence on Chl-a than PMMSST. The monitoring of high-frequency satellite records in the Gulf of California central region provided insight into temporal trends and their association with modes of climate variability. It represents an indicator of the effectiveness of the application of RIs for resilience monitoring that can be used to inform resource management decisions.

Journal of Experimental Marine Biology and Ecology, 2023

This paper reports the effect of dissolved iron (dFe) and dust additions on the Biological Carbon... more This paper reports the effect of dissolved iron (dFe) and dust additions on the Biological Carbon Fixation (BCF) rates in the surface layer of the central Gulf of California (GC). Two on deck experiments were conducted in the summer of 2016 at an oceanographic station located in the Guaymas Basin. Each experiment consisted in the incubation of natural phytoplankton assemblages collected at three distinct depths within the upper 50 m layer and amended either with iron (FeCl3) or dust leachate, followed by the quantification of BCF rates using the 13C assimilation method. A very warm (∼30 °C) water column strongly stratified and with reduced phytoplankton biomass (<1 mg chlorophyll a m−3) was indicative of an oligotrophic environment. In addition, the surface levels of NO3−+NO2− (<0.1 μM), dFe (1.71 ± 1.04 nM), as well as the Fe:N (78 ± 47 nmol μmol−1) and N:P (0.04 ± 0.01) ratios revealed that phytoplankton was under conditions of inorganic nitrogen limitation. BCF rates measured during the experiments ranged between 0.46 ± 0.04 and 6.24 ± 0.34 mg C m−3 h−1 with the highest values at the maximum of fluorescence and their vertical distribution was associated with the carbon biomass of picophytoplankton and diatoms. Despite the oligotrophic condition that predominated during the cruise, most of the Fe or dust additions did not show a significant effect (p > 0.05) on the magnitude of BCF rates, which was attributed to the fact that N, rather than Fe, was the limiting nutrient for phytoplankton production. However, Fe limitation cannot be completely ruled out as two samples (one for each treatment) showed a significant increase (p < 0.05) in BCF rates. We suggest that atmospheric supply of dust during the summer could play a relevant biological role maintaining high concentrations of dFe (and other bioactive metals) in the surface waters of central GC.

Progress in Oceanography, 2023

El Niño in the northeast Pacific and Gulf of California typically causes a decrease in euphausiid... more El Niño in the northeast Pacific and Gulf of California typically causes a decrease in euphausiid abundance (biomass), and modifies their latitudinal biogeographic distributions, but the effect of recent marine heat waves (or their combined effect with El Niño) are less understood. The interannual response of euphausiid community structure and abundance were investigated during the cold–warm transition period (June) of six years (2013–2019, except 2015) in the central Gulf of California, Mexico. Abundance in June 2013–2019 was compared with historical baseline for euphausiid abundance made in June 1957 from a California Cooperative Oceanic Fisheries Investigation cruise, just before El Niño 1957–1958. During 2014–2019 two anomalously warm events occurred: the marine heat wave of 2014 (MHW 2014) and El Niño 2015–2016 (May 2015–May 2016). We tested the hypothesis that the numerically dominant subtropical neritic species Nyctiphanes simplex and temperate oceanic Nematoscelis difficilis significantly decrease in abundance in response to the prolonged warming that occurred during 2014–2016 and that tropical euphausiid species could increase in relative abundance during this period. Ten euphausiid species were collected accounting for < 3% of total relative abundance of 34 zooplankton taxonomic groups collected during June 2013–2014, 2016, 2018 and between 7 and 22.4% during 2017 and 2019. N. simplex and Ne. difficilis accounted for > 80% of euphausiid total abundance during June 2013–2019, with considerably lower abundance during 2013, the MHW 2014, and El Niño 2015–2016 than in June 2017, 2018, and 2019. Mean euphausiid abundance in 2017 and 2019 was slightly higher than that recorded in June 1957. Tropical species increased their relative abundances during El Niño 2015–2016 event, but they were always < 15% of total euphausiid relative abundance during 2013–2019. We estimated that it took at least 3 years for the euphausiid species abundance in the gulf to slowly recover from the unfavorable conditions associated with MHW 2014, and El Niño 2015–2016 to attain highest mean abundance in 2019. Multi–variated ordination analyses showed that the prolonged warming and anomalously low Chl-a concentrations recorded in 2014–2016 negatively influenced euphausiid abundance, a proxy for euphausiid biomass available for pelagic predators in the Gulf of California.

Revista DYNA, 2024

Three molecular assays were used to detect and quantify white spot syndrome virus (WSSV) in DNA e... more Three molecular assays were used to detect and quantify white spot syndrome virus (WSSV) in DNA extracted from seston size-fractioned (0.02, 0.2, 1.2, and 20 μm) samples collected from a coastal lagoon and an adjacent shrimp farm. From 107 DNA extracts, only two from one sample tested positive for WSSV with nested PCR in the 1.2 and 20 μm fractions. These results were confirmed by a semi-quantitative (IQ2000TM WSSV Detection and Prevention System) and a quantitative (IQREALTM WSSV Quantitative System) detection system based, based, respectively, on nested PCR and real-time PCR. A first viral load reference value (6.54 × 104 WSSV copies/mL) was established in a seston size fraction (1.2−20 μm). The results suggest that WSSV could be associated with both resuspension of fine clays and silts, and nanoplankton and organic colloids during infectious events.

Revista de la Academia Colombiana de Ciencias Exactas, Físicas y Naturales, 2021

Phytoplankton is a fundamental productive component of lentic ecosystems, which also directly ref... more Phytoplankton is a fundamental productive component of lentic ecosystems, which also directly reflects environmental variability. This study evaluated the dynamics of phytoplankton in response to the monthly variability of physicochemical properties of a neotropical high Andes reservoir, El Neusa, from July to October 2004. Samples were collected and analyzed for taxonomic identification to species or the lowest possible level and categorized in functional groups (FGs). A total of 111 species of phytoplankton belonging to nine classes and 20 FGs were recorded. Among these phytoplankton classes, Chlorophyceae (36 species), Euglenophyceae (13 species), Bacillariophyceae, (14 species), and Conjugatophyceae (25 species) were the most species-rich and highest in abundance. The overall phytoplankton abundance was largest in August (8.5×104 ±2.7 ×104 ind.L-1) and September (8.9×104 ±4.6×104 ind.L-1); however, the distribution of phytoplankton classes was not statistically different among s...

Ciencias Marinas, 2017

Transparent exopolymer particles (TEP) have been reported as a significant fraction of organic mi... more Transparent exopolymer particles (TEP) have been reported as a significant fraction of organic microgels in different oceans. No TEP data have been published for the California Current region off Baja California that indicate the potential contribution of this reservoir to the carbon budget. We measured TEP in seawater samples, using the spectrophotometric method with alcian blue stain, and additional environmental and biological variables during 3 seasons at coastal stations between ~1.4 and 12.0 mi offshore, near 31ºN. Concentrations of TEP obtained with 0.45 µm pore size filters showed spatial and temporal distributions with a tendency to increase from offshore to nearshore and from winter to summer, respectively, ranging from undetectable values to 7.18 µg XG eq·mL–1 (median: 0.70). A significant positive correlation was observed between the concentration of TEP and bacterioplankton abundance (P < 0.05), and between total organic carbon and bacterioplankton abundance (P < ...

PANGAEA, 2021

This data set includes water column nitrate+nitrite and phosphate concentrations and ancillary CT... more This data set includes water column nitrate+nitrite and phosphate concentrations and ancillary CTD variables from the deep-water region in the southern Gulf of Mexico (GoM). These measurements were used to estimate water mass fractions using an Optimum Multi-parameter analysis that requires semiconservative parameters (NO and PO4* parameters) calculated with nitrate+nitrite, phosphate and dissolved oxygen concentrations. Water samples were collected with a rosette equipped with 12 20-L Niskin bottles during the XIXIMI-5 oceanographic cruise that took place during June 10–25, 2016. The southern region of the GoM (20–26º N, 86–97º W) comprises the deep-waters of the GoM, including the continental slope and abyssal plain. A total of 35 stations were sampled on board R/V Justo Sierra of the National Autonomous University of Mexico. Data columns include sampling Date/Time stamp in ISO format, Longitude, Latitude, Depth, Pressure, temperature and salinity from CTD. The CTD sensors were previously calibrated by the manufacturer, and the accuracy of the measurements was ± 0.001 ºC for temperature, ± 0.002 for salinity, and 2% for DO. Data from the DO sensor were calibrated with data from the Niskin bottle samples, analyzed with the microWinkler method. The accuracy and precision of the microWinkler method were 0.1% and ~ 1.3 µmol/kg, respectively. Nitrate+nitrite and phosphate analyses were performed with a SEAL-AA3-HR auto-analyzer (SEAL Analytical Ltd., Norderstedt, Germany), following the guidelines described in the GO-SHIP Repeat Hydrography Manual. Accuracy and precision were estimated with measurements of certified reference material (CRM) for nutrients (Lots CD and CC; Kanso Co. Ltd., Osaka, Japan). The Ocean Data Standards from the UNESCO were used to assign Quality Flags (QF) for nutrients. The limits of detection (3 SD, n = 11) for nitrate+nitrite and phosphate were 0.037 and 0.028 µmol/kg, respectively. The mean values obtained for nitrate+nitrite from the CD and CC lots were 5.514±0.012 µmol/kg and 30.958±0.047 µmol/kg, respectively. The sum of the certified values for nitrate and nitrate from the CD and CC lots is 5.516±0.050 µmol/kg and 30.996±0.240 µmol/kg, respectively. The mean values obtained for phosphate from the CD and CC lots were 0.447±0.010 µmol/kg and 2.092±0.012 µmol/kg, respectively. The certified values for phosphate from the CD and CC lots is 0.446±0.008 µmol/kg and 2.080±0.019 µmol/kg, respectively.
This research has been funded by the Mexican National Council for Science and Technology - Mexican Ministry of Energy - Hydrocarbon Fund, project 201441. This is a contribution of the Gulf of Mexico Research Consortium (CIGoM, http://www.cigom.info). We acknowledge PEMEX's specific request to the Hydrocarbon Fund to address the environmental effects of oil spills in the Gulf of Mexico. Project: Implementación de redes de observación oceanográficas (físicas, geoquímicas, y ecológicas) para la generación de escenarios ante posibles contingencias relacionadas a la exploración y producción de hidrocarburos en aguas profundas del Golfo de México.

Ciencias Marinas, 2023

In order to determine the structure and biomass of phytoplankton (picophytoplankton, nanodiatoms,... more In order to determine the structure and biomass of phytoplankton (picophytoplankton, nanodiatoms, and microdiatoms) under oligotrophic conditions, a study was carried out in the surface layer of the Guaymas Basin, Gulf of California, during the late summer of 2016. This study included the measurement of hydrographic, chemical, and biological variables in the surface layer of the study area. Our results showed a warm, strongly stratified, and nutrient-depleted water column associated with reduced phytoplankton biomass (<1 mg Chla·m-3). The average ratios of N:P (0.55 ± 1.34), N:Si (0.13 ± 0.18), and Fe:N (52.70 ± 29.70) indicate N-limiting conditions. The biomass contribution of phytoplankton groups fluctuated widely by depth level, with predominance of picophytoplankton (85.0 ± 2.7%) at the surface (5 m) and nano-microdiatoms (91.5 ± 5.9%) at the deepest level (35-40 m), adjacent to the thermocline. Diatoms dominated the integrated biomass between the surface and 50-m depth, with an average contribution ~6 times greater than that of picophytoplankton. Despite the ideal conditions for the proliferation of diazotrophs, the presence of Trichodesmium spp. and Richelia intracellularis was very irregular and in relatively low abundances (2,220 ± 1,575 cell·L-1). Our results are especially relevant as they suggest that, under N-limiting conditions, the paradigm of high biomass and large cell dominance in the Gulf of California may be challenged during the summer season.

Regional Studies in Marine Science, 2019

The heterotrophic ciliates, mainly composed of aloricate (naked) ciliates, are the dominant size ... more The heterotrophic ciliates, mainly composed of aloricate (naked) ciliates, are the dominant size fraction and play an important role in low impacted subtropical coastal systems of central region of the Gulf of California, México, by consuming up to 70% of phytoplankton biomass (pico-and nanoplankton). However , there is no information concerning microzooplankton populations for lagoons highly impacted by anthropogenic activities. This study established a baseline of regional abundance and spatio-temporal variability of aloricate ciliates and tintinnids, in the eutrophic lagoon system Topolobampo-Santa María-Ohuira. Their total abundance ranged from 10 to 56.1×10 3 org L −1 for ciliate, and 10 to 14.80×10 3 org L −1 for tintinnids. Aloricate ciliates mean abundances were approximately four times higher than that of tintinnids, with higher values occurring in winter-spring and punctuated by minor spurts during the rainy months. The study found that eutrophication levels (6.5 to 7.3 TRIX units) were the main factor contributing to their abundance, though tropic interactions and lagoon hydrological characteristics were also relevant. Their distribution revealed that substantial population increases resulted from nutrient enriched residual agricultural drainage at Santa María and Ohuira that exacerbated eutrophication conditions. Canonical correspondence analysis identified that lower values of salinity was due to the influence of wastewater effluent discharge and was the main variable that was related with tintinnids; while dissolved oxygen and chlorophyll-a, variables associated to large primary production, were related to ciliates. The deteriorated water quality of Santa María and Ouhira lagoons likely delineated the low macro-zooplanktonic biomasses and consequently the higher aloricate ciliates and tintinnids abundances.

Estudios recientes en el océano Pacifico mexicano, Dec 14, 2018

En este estudio se reportan observaciones microscópicas de epifluorescencia de muestras recolecta... more En este estudio se reportan observaciones microscópicas de epifluorescencia de muestras recolectadas en el sitio de Cuenca Alfonso, Bahía de La Paz. Se detectaron emisiones de fluorescencia citoplásmica verde de Phalacroma doryphorum y fluorescencia verde y amarillo / naranja por simbiontes en consorcios con dinoflagelados (Ornithocercus e Histioneis) y diatomeas (Rizosolenia). Estos consorcios están comúnmente presentes en las comunidades planctónicas con la entrada del agua superficial tropical oligotrófica durante la temporada de verano en el sur del Golfo de California.

Temporal and spatial changes of virioplankton abundance (VLP), chlorophyll-a (Chl-a) concentratio... more Temporal and spatial changes of virioplankton abundance (VLP), chlorophyll-a (Chl-a) concentration, and some environmental variables, were assessed from October 2004 to April 2005 at four sampling sites in a high-mountain reservoir in the Colombian Andes. VLP ranged from 2.4-10.5×10 7 and 3.6-6.5×10 7 VLP mL −1 in the samples from the photic zone and hypolimnion, respectively. Surface VLP showed a progressive increase from November to April in the limnetic zone, and until February in the littoral stations. This trend coincided with the gradual increase of the water column stratification, as well as the augment of the reservoir hydraulic volume. Principal components analysis showed a grouping of environmental (dissolved oxygen, pH, water temperature) and biological variables (VLP, Chl-a, bacterioplankton abundance and biomass) within the first component (26.4% of explained variance), associated to an increase of photosynthetic activity, as a potential supplement of organic substrates to heterotrophic viral hosts. High values of virus-to-prokaryote ratio (VPR), and a negative relationship between VLP and average biomass per prokaryotic cell, indicate strong viral control which is probably more intense on active and larger cells. These results provide a framework for understand the virioplankton responses to regional hydrological conditions and hydraulic behavior of this reservoir. The spatiotemporal scale of this study does not allow to confirm that viral dynamics is significantly affected by human activities causing potential alterations on nutrient cycling.

Influence of agriculture and aquaculture activities on the response of autotrophic picoplankton in Laguna Macapule, Gulf of California (Mexico), 2017

Introduction: The lagoon is a component of coastal zones, whose populations of autotrophic picopl... more Introduction: The lagoon is a component of coastal zones, whose populations of autotrophic picoplankton (APP) remain largely unstudied. These lagoons display high-nutrient productivity and additionally may also be subjected to anthropogenic activities. This study selected Laguna Macapule, located on the eastern shore in the mid-region of the Gulf of California, due to the fact that a drainage network servicing the surrounding agricultural region (>230,000 hectares under cultivation) directs irrigation runoff, shrimp farm effluents, and urban wastewater containing large quantities of nutrients to be discharged into this lagoon. We propose to identify the APP's response to various types of environmental and anthropogenic influence in this highly impacted coastal lagoon. Methods: Two sites (separated by 2.7 km) were monitored from December 2007 to December 2008. One, located at the entrance to Laguna Macapule (oceanic influence) and the other a discharge canal (eutrophic conditions) inside the lagoon at El Tortugón. Results: APP was the numerically dominant phytoplankton fraction (15 × 10 6 to 620 × 10 6 cells L −1) with coccoidal cyanobacteria as the dominant fraction throughout the year. Peak levels were reached in spring-early autumn and they were the second largest contributor to biomass. Abundance of APP cells corresponds to the lagoon's eutrophic status. Maximum numbers and a higher average of APP were recorded at the El Tortugón channel during the warm season (months with SST higher than 24 °C). The general positive relationship of the APP's annual cycle at both sites as well as a negative relationship with heterotrophic nanoflagellates (HNF) abundance, supports the idea that natural forcing, in particular sea surface temperature (SST) is the predominant influences on APP's seasonal variability.

Vertical and seasonal distribution of the biogeochemical tracer N* was estimated to delineate the... more Vertical and seasonal distribution of the biogeochemical tracer N* was estimated to delineate the key pathways that regulate nitrogen in the Alfonso Basin, Bay of La Paz, between February 2012 - March 2013. We used data of dissolved inorganic nitrogen (DIN) and phosphorus (DIP) concentrations from four levels in the euphotic zone (100, 33, 3, and 0.1% I0) and another four depths below it (150, 200, 250 and 300 m). For the calculation of N*, its constants were reestimated from the original equation based on historical data of nutrients compiled between December 2005 - December 2012. Detection of anomalies on the mean ratio of NID:DIP (13.16) indicated a predominance of negative values corresponding to a greater removal of NID, especially below the 150 m, under hypoxic conditions (< 1.4 mg l-1) and during periods of high biological production for the area. The incidence of these values could be associated to the local denitrification process, as well as advection of water masses from the Tropical Eastern Pacific. Positive values were evident on surface from May until the end of the study in most part of the euphotic layer, with higher intensity between August - October, December and March 2013, suggesting an increase of the relative importance of biological N2 fixation on denitrification. The application of the tracer N* indicates that the participation of both N2 fixation and denitrification in the basin are active mechanisms of regulation of the nitrogen cycle. Future efforts will focus on the determination of rates of these physiological pathways.
Keywords: Alfonso Basin, dissolved inorganic nitrogen, dissolved inorganic phosphorus, N* biogeochemical tracer.

The contribution of bacterioplankton (BP) to the planktonic food web, as well as environmental an... more The contribution of bacterioplankton (BP) to the planktonic food web, as well as environmental and biological factors involved in its control remains unexplored in tropical high mountain environments. In a tropical high-mountain aquatic system of Colombian, Neusa reservoir, the spatial and temporal dynamics of abundance, biovolume and biomass of BP were evaluated in relation to environmental variability and density of autotrophic nanoplankton (NA) and heterotrophic nanoflagellates (NFH). There was no clear association between BP dynamics and nutrients. However, this relationship appeared to be indirect through stimulation of NA production during periods of increased mixing and rainfall. The highest BP abundances and biomasses were detected in the littoral station in consistency with low numbers of NFH and potential organic inputs derived from macrophytes. The total cellular carbon and average cell biovolume of BP were weakly correlated with the dynamics of NFH, which was attributed to the predominance of phosphorus-limiting conditions and potential removal of NFH and BP by larger zooplankton fractions (> 20 microns). Approximately, 60% of the total prokaryotic biomass was provided by small sizes (<0.18 μm3). The data suggest that the distribution of cell biovolume could be the result of the synergistic effect between nutrient limitation and selective grazing. BP dynamics in the Neusa reservoir indicates the existence of a slightly fluctuating carbon reservoir and an inefficient carbon transfer through the microbial loop to higher trophic levels.
Key words: Autotrophic nanoplankton, bacterioplankton, heterotrophic nanoflagellates, high mountain, Neusa Reservoir.

Composition of metals in suspended particulate matter of Alfonso basin, southern Gulf of California, Jan 15, 2016

Suspended particulate matter residues collected by 0.4 μm pore size filters were analyzed for 9 t... more Suspended particulate matter residues collected by 0.4 μm pore size filters were analyzed for 9 trace metals (Mp) and phosphorus (Pp) from seawater samples taken from depths ranging from 0–300 m. The samples were obtained from a marginal basin located in southwestern Gulf of California. Four different sampling trips occurred during the year to coincide with periods of known contrasting hydrographic conditions. The depth-integrated concentration values followed the sequence Fe>Pp>Zn>Cu>Ni>Mo>Cd>Pb>V>Co. Temporal and vertical distribution of the largest concentrations of Mp and Mp/Pp trace metals with their concentrations normalized to phosphorus were consistent with enrichment processes in March and May. These were respectively associated with intense mixing and a submesoscale cyclonic eddy. The highest abundances of autotrophic picoplankton and nanoplankton, diatoms and dinoflagellates and chlorophyll a concentrations were also noted at this time. Wind speed was the only environmental variable that correlated positively (Spearman, p<0.05) with the temporal distribution of most of the Mp trace metals (except Cd, Co and V) in the euphotic zone, which was attributed to increases in the eolic contribution, sediment resuspension and horizontal transport towards the basin. The biological significance of Fe, Cu, Ni, Mo and V is discussed within the document based on the detected significant correlations with phytoplankton-assessed components. Our observations suggest a link between environmental forcing, the entrainment of metals and phytoplankton response as a reservoir of these metals in the euphotic zone, and as a possible source of replenishment for remineralization in the deeper layer. Future research should corroborate the assumptions about the origin and dynamics of dissolved and particulate fractions of metals and influence the biological activity and biogeochemistry of these elements in the basin.

In May 2012, rates of Nitrogen- fixation (NF) rates were determined for first time in the euphoti... more In May 2012, rates of Nitrogen- fixation (NF) rates were determined for first time in the euphotic zone (0-43m) and at 150m depth using the high-sensitive 15N2 tracer method at Alfonso Basin, Gulf of California. In this study high rates (437 μmol N m-2 d-1, depth integrated 0-150 m) were estimated under conditions of nutrient enrichment and the expansion of hypoxic conditions relative to others observations. Filamentous cyanobacteria were not observed and Synechococcus spp. a potential diazotroph accounted for over 70% and ~43% of the total density of autotrophic picoplankton. This suggested the participation of Synechococcus in the Nitrogen-fixation pathway.

Thesis Chapters by Cristian Hakspiel

The role of bacterioplankton in planktonic food webs and their controlling factors in high-mounta... more The role of bacterioplankton in planktonic food webs and their controlling factors in high-mountain Andean aquatic systems are poorly understood. The abundance of bacterioplankton and its biovolume was studied monthly between July 2004 and April 2005 at different sampling sites of the Neusa Reservoir (Cundinamarca, Colombia) using the epifluorescence microscopy technique coupled with image analysis, together with the measurement of different environmental variables and abundance of nanozooplankton. The abundance of bacterioplankton was generally higher during the period of water column mixing conditions (July and August) and showed a decrease from the littoral zone to the limnetic zone. Regarding cell morphology, a higher proportion of large and elongated forms was detected between July and November, indicating a higher availability of substrates for its growth. Some of the bacterioplankton variability appeared to be influenced by the hydraulic and hydrological functioning of the reservoir and by the hydrological conditions of the region that indirectly stimulate the production of phytoplankton and aquatic macrophytes. The abundance of nanozooplankton was greater in the limnetic zone than in the litoral zone, and between September and November. The variation of the bacterioplankton to nanozooplankton ratio (CBP) indicates an intensification of predation pressure in the limnetic zone, as well as a general decrease from September to March. These two components show a statistical relationship (Spearman, r= 0.37, p <0.05), suggesting the dependence of the predator on the numerical availability of the prey, and possibly also on the optimal biovolume range of the bacterioplankton that can be ingested. The spatio-temporal behavior of the microbial components and their interactions observed in this work confirms a marked variability that must be considered to characterize the environmental conditions of the Neusa Reservoir ecosystem. Future efforts should focus on the understanding of various controlling factors on bacterioplankton in high mountain Andean systems, as well as the study of the biogeochemical role of prokaryotic populations and their contribution to nutrient budget.

Laguna de Macapule, Sinaloa is an eutrophic and shallow aquatic system with nitrogen limited cond... more Laguna de Macapule, Sinaloa is an eutrophic and shallow aquatic system with nitrogen limited conditions for phytoplankton growth. It suggests an important participation of planktonic microorganism recycling nutrients and supporting ecosystem food webs. To estimate their participation, we quantified microbial components monthly from December 2007 to December 2008 in two points of Macapule (estuary and entrance). Also, in these same fractions was determined their possible association to white spot syndrome virus (WSSV) in the lagoon and in two sites (reservoir and pond) at shrimp farm Doña Juana by means of molecular analysis. Some autotrophic fractions, like autotrophic picoplankton (PA) and microphytoplankton (MF) were different between both location sampling. This defined a bimodal production cycle with two seasonal peaks: spring and summer-autumn. The former increase was characterized by larger MF densities in the Macapule entrance, which were favored by high dissolve inorganic Nitrogen and silica concentration derived from coastal upwelling and agricultural activities. The second peak in the estuary occurred under strong Nitrogen:Phosphorus (N:P) unbalance and was associated to PA, cyanobacterial trycome and some diatoms predominance. Bacterioplankton, virioplankton and nannoplankton dynamics were similar between both sites. These two first components were tightly related with some phytoplanktonic blooms in the cold period (January-April) indicating a high available organic substrates and hosts. During this period, the virus-microorganism ratio registered high values suggesting a stronger viral control. Stimulated PA abundance at ending spring and early summer was related to water temperature and dissolve inorganic phosphorus increase. Their densities were usually higher in the estuary than the entrance because of possible microzooplankters grazing loss unbalance and some differences in their taxonomic structure from both sites. A significant contribution of mixotrophic and Nitrogen fixing populations was a feature of the phytoplankton community from Macapule lagoon. This study revealed that microbial food web in Macapule is favored by eutrophization process. This condition suggests that much of the organic carbon flux is retained by the microbial components. The WSSV was associated with nano-and microplankton fractions only in the pond during high levels of infectious events. The low detection during the annual cycle and in <2.0 μm fractions could be related to low concentrations of virus in the water sample, as long as the possible occurrence of genetic variables in viral sequences corresponding to the hybridization sites of primers in each PCR analysis.

Some sources and biogeochemical processes of the nitrogen cycle were studied to determine the exi... more Some sources and biogeochemical processes of the nitrogen cycle were studied to determine the existing balance of this nutrient in the first 300 m of the water column of Alfonso Basin. The seasonal variability of microbial planktonic abundances were described, as well as, their association to the carbon assimilation (AC) levels, organic production and physicochemical variables. The dynamics of the thermohaline, during the process of winter mixing and the elevation of deep water due to pumping (April to July) of a cyclonic eddy caused a prolonged period of high levels of oxidized nutrients, which resulted in high planktonic abundances. However, this increase generally was restricted to the uppermost layer, where according to canonical correspondence analysis, the planktonic components were positively associated to dissolved oxygen and temperature. Estimated annual AC values in the euphotic zone (Zeu) were substantially higher (6741 kg C ha-1 yr-1) compared to previous reports for the Gulf of California, where the fraction between 0.4 to 20 μm had a contribution of ~ 63 %. At 150 m depth, AC rates fluctuated between 0.26-3.2 mg C m-3 h-1 which were attributed to both the activity of chemolithotrophic organisms, as well as phytoplankton groups adapted to very low irradiances, which were consistent with their densities distribution. Among the evaluated nitrogen inputs, vertical transport of nitrate due to cyclonic eddy was the most important for the Zeu (63 kg N ha-1 yr-1), followed by biological N2 fixation (FBN) and atmospheric deposition of gas + aerosol (26 and 7 kg N ha-1 yr-1, respectively). FBN registered large values compared to previous measurements for the Gulf of California and other coastal and oceanic systems, as well as detection levels at 150 m depth under high concentration of dissolved inorganic nitrogen suggesting a positive feedback due low nitrogen to phosphorus ratio. Between 100-300 m, nitrogen losses by N2 production via denitrification and ANAMMOX were low compared to observed rates in sites of the Pacific oxygen minimum zones. Likewise, ANAMMOX was predominant (79%) relative to denitrification. This characteristic was attributed mainly to the physiological inhibition by relatively high dissolved oxygen content at the site (0.15-1.72 ml O2 l-1), the presence of denitrification inhibitors (e.g. H2S and HS-), and/or unevaluated production and consumption of intermediate forms such as N2O. Nitrification in the aphotic layer as a mechanism for regeneration of dissolved inorganic forms, showed a high contribution to the mobilization of nitrogen (251 kg N Ha-1 yr-1) compared to other physiological rates, and integrated values were similar to previous estimates of nitrification for the Zeu of the Gulf of California and Mexican Pacific Ocean. However, the temporal variability of these rates was strongly associated with the availability of substrates (e.g. nitrite and ammonium) during periods of high biological production. Indirect calculations of assimilation of dissolved inorganic nitrogen from AC rates corroborate the prevalence of this activity in the mobilization of nitrogen in the Zeu (949 kg N ha-1 yr-1). Indirect calculations of dissolved inorganic nitrogen assimilation through AC rates corroborate the predominance of this activity to the mobilization of nitrogen in the euphotic layer (949 kg N Ha-1 yr-1). The nitrogen budget indicated that external inputs and nitrification in the first 300 m depth barely contributed with 53% of the requirement of this element for phytoplankton growth organisms. This suggests the presence of alternative routes or reservoirs associated with the dissolved organic fraction as a nitrogen supply mechanism for mixotrophic populations. Clearly the results provided by this study indicate a highly dynamic cycle of nitrogen and its potential for positive feedback nitrogen inventory to mitigate the N:P unbalance prevailing in Cuenca Alfonso.

Book Reviews by Cristian Hakspiel

Mecanismos que regulan el nitrógeno en el océano: Influencias potenciales sobre la razón isotópica del nitrógeno (δ15N) , Jun 19, 2013

El presente libro abarca varios temas relacionados con el ciclo biogeoquímico de nitrógeno en el ... more El presente libro abarca varios temas relacionados con el ciclo biogeoquímico de nitrógeno en el océano. Incluye algunos aspectos de las especies químicas dominantes, sus transformaciones y los procesos biológicos y ambientales más relevantes que rigen el inventario de este elemento, y que a su vez promueven la distribución global de los principales grupos funcionales del fitoplancton. Así mismo, se profundiza en las aplicaciones de las razones isotópicas del nitrógeno (δ15N) para la identificación de las fuentes y rutas, tanto de origen natural como antropogénico, y la influencia de los factores físicos y la actividad biológica en la modulación de la señal isotópica en el nitrato y el material orgánico particulado en el océano. Particularmente, se enfatiza en los procesos fisiológicos de fijación de N2 y desnitrificación como principales procesos de aporte y remoción de nitrógeno, respectivamente. Ambos procesos se tratan con relación a la distribución del déficit de nitrógeno y del δ15N en la columna de agua de las cuencas oceánicas, y en coherencia con cambios ambientales de corto, mediano y largo plazo, deducidos a partir de modelos geoquímicos y registros paleoceanográficos.