Helmut Maske | Centro de Investigación Científica y de Educación Superior de Ensenada, BC. (original) (raw)

Papers by Helmut Maske

Research paper thumbnail of High-Sustained Concentrations of Organisms at Very low Oxygen Concentration Indicated by Acoustic Profiles in the Oxygen Deficit Region Off Peru

Frontiers in Marine Science, 2021

The oxygen deficient mesopelagic layer (ODL) off Peru has concentrations below 5 μmol O2 kg–1 and... more The oxygen deficient mesopelagic layer (ODL) off Peru has concentrations below 5 μmol O2 kg–1 and is delimited by a shallow upper oxycline with strong vertical gradient and a more gradual lower oxycline (lOx). Some regions show a narrow band of slightly increased oxygen concentrations within the ODL, an intermediate oxygen layer (iO2). CTD, oxygen and lowered Acoustic Doppler Current Profiler (LADCP, 300 kHz) profiles were taken on the shelf edge and outside down to mostly 2000 m. We evaluate here the acoustic volume backscatter strength of the LADCP signal representing organisms of about 5 mm size. Dominant features of the backscatter profiles were a minimum backscatter strength within the ODL, and just below the lOx a marked backscatter increase reaching a maximum at less than 3.0 μmol O2 kg–1. Below this maximum, the acoustic backscatter strength gradually decreased down to 1000 m below the lOx. The backscatter strength also increased at the iO2 in parallel to the oxygen concentr...

Research paper thumbnail of Free-rising, tethered CTD profiler: increased vertical resolution and near surface profiling

Limnology and Oceanography: Methods, 2012

ABSTRACT The formation of a diurnal thermocline at few meters depth is difficult to document beca... more ABSTRACT The formation of a diurnal thermocline at few meters depth is difficult to document because of the mixing induced by research platforms. We built a free-rising CTD-platform, including sensors for chlorophyll fluorescence, turbidity, and light, that profiles to similar to 0.4 m below the surface with better than 0.03 m resolution and at sufficient distance from the research platform to measure an undisturbed water column. The profiler, with a practical maximum depth of 100 m is controlled mechanically using sacrificial weights and a safety tether that assures easy recovery of the instrument. The design concept is easily adapted to many commercial CTD models. Off Baja California, most profiles showed temperature stratification near the surface and some profiles showed near surface chlorophyll fluorescence thin layers; these features would be difficult to observe with normal CTD profilers.

Research paper thumbnail of A non-amplified FISH protocol to identify simultaneously different bacterial groups attached to eukaryotic phytoplankton

Journal of Applied Phycology, 2014

ABSTRACT Eukaryotic phytoplankton and bacteria form complex trophic interactions in nature and cu... more ABSTRACT Eukaryotic phytoplankton and bacteria form complex trophic interactions in nature and cultures. The interaction will depend on the spatial arrangement but the architecture of these arrangements has been little investigated. Here we modified a protocol to identify and localize multiple bacterial taxa attached to phytoplankton cells in culture and natural samples, including sensitive dinoflagellates. Samples were embedded in agarose and hybridized simultaneously with different probes of distinct fluorescence properties. Embedding avoided losses or damage of host cells and preserved the attached bacteria during hybridization and washing. Embedding still allowed efficient hybridization and identification of intact host cells. After fluorescence in situ hybridization of the bacteria the phytoplankton host cells, including dinoflagellates were still intact. Digital image stacks taken with a wide field epifluorescence microscope using different excitation– emission wavelength combinations allow the location of the different bacterial groups on the host cell surface and the spatial relationship of the different bacterial groups.

Research paper thumbnail of Correction: Maintenance of Coastal Surface Blooms by Surface Temperature Stratification and Wind Drift

PLoS ONE, 2013

The following information is missing from the Funding Statement: The Mexican CONACyT funded this ... more The following information is missing from the Funding Statement: The Mexican CONACyT funded this project (CB--2008-01 106003) and provided the doctoral fellowship to MC Ruiz de la Torre.

Research paper thumbnail of Ecohab: Hyperspectral Optical Properties of Red-Tide Blooms

The goal of our project is the bio-optical characterization of dinoflagellate and other red-tide ... more The goal of our project is the bio-optical characterization of dinoflagellate and other red-tide blooms, to facilitate the optical detection and monitoring of these blooms from above the sea surface.

Research paper thumbnail of Adsorption of Dissolved Organic Matter to the Inorganic Filter Substrate and Its Implications for 14C Uptake Measurements

Applied and Environmental Microbiology, 1994

Inorganic carbon uptake rates for glass fiber-filtered samples are higher than those for membrane... more Inorganic carbon uptake rates for glass fiber-filtered samples are higher than those for membrane-filtered samples because of adsorption of dissolved organic matter to the filter substrate. Experimentally derived values for adsorption onto filters were as follows (relative units): GF/F filter, 1, quartz filter, 1.1, GF/C filter, 0.6; GN-6 Gelman filter, 0.1; Nuclepore and Poretics filter, 0.0; Anodisc filter, 0.4 to 1.9.

Research paper thumbnail of Abundance Of Coccoid Cyanobacteria, Hydrographic Parameters And The Possible Underestimation Of In Situ Chlorophyll a In The Northern Gulf Of California And The Mexican California Current

Ciencias Marinas, 2000

The abundance of coccoid cyanobacteria was counted within the euphotic zone at a station in Delfí... more The abundance of coccoid cyanobacteria was counted within the euphotic zone at a station in Delfín Basin, in the northern Gulf of California, and at a station in the California Current, off Todos Santos Bay, during 1993. The abundance of cyanobacteria at both stations was between 107 and 108 cells L–1. Comparison with other concomitantly sampled parameters, i.e., irradiance, temperature, nutrients and chlorophyll a, showed no significant correlation with the cyanobacterial abundance. The contribution of cyanobacteria to the total in situ chlorophyll a concentration was calculated using the cyanobacterial abundance, an average published value of 1.0fgChl a cell–1 and a reduced pigment extraction efficiency in cyanobacteria. Cyanobacteria contributed, in half of the cases, more than 10% and more than 4% of the total chlorophyll in Delfín Basin and the California Current, respectively. Again, this relative contribution was not related to the other concomitantly measured in situ paramet...

Research paper thumbnail of Temporal and spatial distribution of transparent exopolymer particles off the northern coast of Baja California, Mexico

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 < ...

Research paper thumbnail of Euphotic depth, irradiance attenuation and remote sensing k490 in bio-optical provinces of the gulf of california

Ciencias Marinas, 2000

Algorithms are presented using remote sensing optical depth, 1/K490, to estimate the depth of the... more Algorithms are presented using remote sensing optical depth, 1/K490, to estimate the depth of the euphotic zone and depths where spectral irradiance at 490 nm are 10%, 3%, 1% and 0.3% of incident surface value. The linear empirical models are derived using data from radiometric profiles measured at various locations in the Gulf of California during cruises in 1995, 1997 and 1998. The models apply to three geographically and temporally separate bio-optical provinces of the gulf: the northern basin, the Midriff Islands and the southern basins. Relative uncertainties of the regression models for the 1% light depths for both spectral irradiance (490 nm) and EPAR range from approximately 5% in the northern basin to 10% in the southern basins.

Research paper thumbnail of Euphotic depth, irradiance attenuation and remote sensing k490 in bio-optical provinces of the gulf of california

Ciencias Marinas, 2000

Algorithms are presented using remote sensing optical depth, 1/K490, to estimate the depth of the... more Algorithms are presented using remote sensing optical depth, 1/K490, to estimate the depth of the euphotic zone and depths where spectral irradiance at 490 nm are 10%, 3%, 1% and 0.3% of incident surface value. The linear empirical models are derived using data from radiometric profiles measured at various locations in the Gulf of California during cruises in 1995, 1997 and 1998. The models apply to three geographically and temporally separate bio-optical provinces of the gulf: the northern basin, the Midriff Islands and the southern basins. Relative uncertainties of the regression models for the 1% light depths for both spectral irradiance (490 nm) and EPAR range from approximately 5% in the northern basin to 10% in the southern basins.

Research paper thumbnail of The Vitamin B1 and B12 Required by the Marine Dinoflagellate Lingulodinium polyedrum Can be Provided by its Associated Bacterial Community in Culture

Frontiers in microbiology, 2016

In this study we established the B1 and B12 vitamin requirement of the dinoflagellate Lingulodini... more In this study we established the B1 and B12 vitamin requirement of the dinoflagellate Lingulodinium polyedrum and the vitamin supply by its associated bacterial community. In previous field studies the B1 and B12 demand of this species was suggested but not experimentally verified. When the axenic vitamin un-supplemented culture (B-ns) of L. polyedrum was inoculated with a coastal bacterial community, the dinoflagellate's vitamin growth limitation was overcome, reaching the same growth rates as the culture growing in vitamin B1B7B12-supplemented (B-s) medium. Measured B12 concentrations in the B-s and B-ns cultures were both higher than typical coastal concentrations and B12 in the B-s culture was higher than in the B-ns culture. In both B-s and B-ns cultures, the probability of dinoflagellate cells having bacteria attached to the cell surface was similar and in both cultures an average of six bacteria were attached to each dinoflagellate cell. In the B-ns culture the free bacte...

Research paper thumbnail of Carbono en ecosistemas acuáticos de México

En este libro se conjunta la información aportada por algunos de los estudiosos de los diferentes... more En este libro se conjunta la información aportada por algunos de los estudiosos de los diferentes componentes del ciclo del carbono en los sistemas acuáticos. Se presenta un panorama de lo que actualmente se conoce sobre algunos procesos biogeoquímicos relacionados con el carbono y la posible contribución de los diferentes ecosistemas al balance temporal de este elemento. Además, se pone de manifiesto la falta de conocimiento del ciclo del carbono en algunos sistemas costeros y oceánicos, así como la necesidad apremiante de realizar un mayor esfuerzo en algunos campos de la investigación en los mares mexicanos.

Research paper thumbnail of Multidisciplinary Observing in the World Ocean’s Oxygen Minimum Zone Regions: From Climate to Fish — The VOICE Initiative

Frontiers in Marine Science, 2019

Multidisciplinary ocean observing activities provide critical ocean information to satisfy ever-c... more Multidisciplinary ocean observing activities provide critical ocean information to satisfy ever-changing socioeconomic needs and require coordinated implementation. The upper oxycline (transition between high and low oxygen waters) is fundamentally important for the ecosystem structure and can be a useful proxy for multiple observing objectives connected to eastern boundary systems (EBSs) that neighbor oxygen minimum zones (OMZs). The variability of the oxycline and its impact on the ecosystem (VOICE) initiative demonstrates how societal benefits drive the need for integration and optimization of biological, biogeochemical, and physical components of regional ocean observing related to EBS. In liaison with the Global Ocean Oxygen Network,

Research paper thumbnail of Modulation of the vertical particle transfer efficiency in the oxygen minimum zone off Peru

Biogeosciences, 2018

The fate of the organic matter (OM) produced by marine life controls the major biogeochemical cyc... more The fate of the organic matter (OM) produced by marine life controls the major biogeochemical cycles of the Earth's system. The OM produced through photosynthesis is either preserved, exported towards sediments or degraded through remineralisation in the water column. The productive eastern boundary upwelling systems (EBUSs) associated with oxygen minimum zones (OMZs) would be expected to foster OM preservation due to low O 2 conditions. But their intense and diverse microbial activity should enhance OM degradation. To investigate this contradiction, sediment traps were deployed near the oxycline and in the OMZ core on an instrumented moored line off Peru. Data provided high-temporal-resolution O 2 series characterising two seasonal steady states at the upper trap: suboxic ([O 2 ] < 25 µmol kg −1) and hypoxic-oxic (15 < [O 2 ] < 160 µmol kg −1) in austral summer and winter-spring, respectively. The OMZ vertical transfer efficiency of particulate organic carbon (POC) between traps (T eff) can be classi-Published by Copernicus Publications on behalf of the European Geosciences Union.

Research paper thumbnail of Adsorption ofDissolved Organic Matter totheInorganic Filter Substrate andItsImplications for14CUptakeMeasurements

aluminum oxide, honeycomb porepattern (Anodisc), pore size, 0.2,um;(v)membrane, mixedcellulose ac... more aluminum oxide, honeycomb porepattern (Anodisc), pore size, 0.2,um;(v)membrane, mixedcellulose acetate and cellulose nitrate, GN-6(Whatman), poresize, 0.45jum; and (vi) polycarbonate Nuclepore andPoretics, black, poresize, 0.2 ,um. Thefilters werebrought into contact withtheradioactive DOM solution bytwoalternative methods: thefilter was dipped intothesolution orthefilter washeldinavacuum filtration device andthesolution wasfiltered through it. After thefilter contacted theradioactive DOM solution, thefilter wasrinsed withanonradioactive DOM solution prepared in thesamewayastheradioactive DOM solution. Thefilter was transferred toascintillation vial, 0.5mlof1N HClwasadded, andthevialwasleft toventforatleast 24h atroom temperature andcounted (Beckman LS 5000scintillation counter; Universol cocktail (ICNRadiochemicals)). Insome

Research paper thumbnail of Of The Effect Of Mesoscale Structures On The Deep Chlorophyll And Particle Maxima At The Entrance To The Gulf Of California

The entrance to the Gulf of California is characterized by the convergence of three surface water... more The entrance to the Gulf of California is characterized by the convergence of three surface water masses resulting in a complex mesoscale field. The effects of such structures on the deep chlorophyll maximum, an ubiquitous feature of many oceanic regions, is not well known. An interdisciplinary oceanographic survey was carried out in February-March 2005. The main goal was to study the effect of mesoscale eddies on the biology of an oligotrophic ocean. Several cyclonic and anticyclonic structures were found as well as a narrow and intense current jet off the coast of Baja California. Inside cyclonic/anticyclonic eddies a relative increase/decrease of both chlorophyll and dissolved oxygen concentration is clearly observed. The deep chlorophyll maximum is found positioned above the thermocline throughout the survey. Higher concentrations are found inside the deep chlorophyll maximum inside the cyclonic eddy and in the deep chlorophyll maximum of the coastal jet. The latter case is cons...

Research paper thumbnail of The Chemical Transformation of the Cellular Toxin INT (2-(4-Iodophenyl)-3-(4-Nitrophenyl)-5-(Phenyl) Tetrazolium Chloride) as an Indicator of Prior Respiratory Activity in Aquatic Bacteria

International Journal of Molecular Sciences, 2019

In the ocean, the prokaryote respiration rates dominate the oxidation of organics, but the measur... more In the ocean, the prokaryote respiration rates dominate the oxidation of organics, but the measurements may be biased due to pre-incubation size filtration and long incubation times. To overcome these difficulties, proxies for microbial respiration rates have been proposed, such as the in vitro and in vivo estimation of electron transport system rates (ETS) based on the reduction of tetrazolium salts. INT (2-(4-Iodophenyl)-3-(4-Nitrophenyl)-5-(Phenyl) Tetrazolium Chloride) is the most commonly applied tetrazolium salt, although it is toxic on time scales of less than 1 h for prokaryotes. This toxicity invalidates the interpretation of the rate of in vivo INT reduction to formazan as a proxy for oxygen consumption rates. We found that with aquatic bacteria, the amount of reduced INT (F; µmol/L formazan) showed excellent relation with the respiration rates prior to INT addition (R; O2 µmol/L/hr), using samples of natural marine microbial communities and cultures of bacteria (V. harvey...

Research paper thumbnail of INT (2-(4-Iodophenyl)-3-(4-Nitrophenyl)-5-(Phenyl) Tetrazolium Chloride) Is Toxic to Prokaryote Cells Precluding Its Use with Whole Cells as a Proxy for In Vivo Respiration

Microbial Ecology, 2015

Prokaryote respiration is expected to be responsible for more than half of the community respirat... more Prokaryote respiration is expected to be responsible for more than half of the community respiration in the ocean, but the lack of a practical method to measure the rate of prokaryote respiration in the open ocean resulted in very few published data leaving the role of organotrophic prokaryotes open to debate. Oxygen consumption rates of oceanic prokaryotes measured with current methods may be biased due to pre-incubation size filtration and long incubation times both of which can change the physiological and taxonomic profile of the sample during the incubation period. In vivo INT reduction has been used in terrestrial samples to estimate respiration rates, and recently, the method was introduced and applied in aquatic ecology. We measured oxygen consumption rates and in vivo INT reduction to formazan in cultures of marine bacterioplankton communities, Vibrio harveyi and the eukaryote Isochrysis galbana. For prokaryotes, we observed a decrease in oxygen consumption rates with increasing INT concentrations between 0.05 and 1 mM. Time series after 0.5 mM INT addition to prokaryote samples showed a burst of in vivo INT reduction to formazan and a rapid decline of oxygen consumption rates to zero within less than an hour. Our data for non-axenic eukaryote cultures suggest poisoning of the eukaryote. Prokaryotes are clearly poisoned by INT on time scales of less than 1 h, invalidating the interpretation of in vivo INT reduction to formazan as a proxy for oxygen consumption rates.

Research paper thumbnail of Substrate-Limited and -Unlimited Coastal Microbial Communities Show Different Metabolic Responses with Regard to Temperature

Frontiers in Microbiology, 2017

Bacteria are the principal consumers of dissolved organic carbon (DOC) in the ocean and predation... more Bacteria are the principal consumers of dissolved organic carbon (DOC) in the ocean and predation of bacteria makes organic carbon available to higher trophic levels. The efficiency with which bacteria convert the consumed carbon (C) into biomass (i.e., carbon growth efficiency, Y) determines their ecological as well as biogeochemical role in marine ecosystems. Yet, it is still unclear how changes in temperature will affect Y and, hence, the transfer of consumed C to higher trophic levels. Here, we experimentally investigated the effect of temperature on metabolic functions of coastal microbial communities inoculated in both nutrient-limited chemostats and nutrient-unlimited turbidostats. We inoculated chemostats and turbidostats with coastal microbial communities into seawater culture medium augmented with 20 and 100 µmol L −1 of glucose respectively and measured CO 2 production, carbon biomass and cell abundance. Chemostats were cultured between 14 and 26 • C and specific growth rates (µ) between 0.05 and 6.0 day −1 , turbidostats were cultured between 10 and 26 • C with specific growth rates ranging from 28 to 62 day −1. In chemostats under substrate limitation, which is common in the ocean, the specific respiration rate (r, day −1) showed no trend with temperature and was roughly proportional to µ, implying that carbon growth efficiency (Y) displayed no tendency with temperature. The response was very different in turbidostats under temperature-limited, nutrient-repleted growth, here µ increased with temperature but r decreased resulting in an increase of Y with temperature (Q 10 : 2.6). Comparison of our results with data from the literature on the respiration rate and cell weight of monospecific bacteria indicates that in general the literature data behaved similar to chemostat data, showing no trend in specific respiration with temperature. We conclude that respiration rates of nutrient-limited bacteria measured at a certain temperature cannot be adjusted to different temperatures with a temperature response function similar to Q 10 or Arrhenius. However, the cellular respiration rate and carbon demand rate (both: mol C cell −1 day −1) show statistically significant relations with cellular carbon content (mol C cell −1) in chemostats, turbidostats, and the literature data.

Research paper thumbnail of INT (2-(4-Iodophenyl)-3-(4-Nitrophenyl)-5-(Phenyl) Tetrazolium Chloride) Is Toxic to Prokaryote Cells Precluding Its Use with Whole Cells as a Proxy for In Vivo Respiration

Microbial Ecology, 2015

Prokaryote respiration is expected to be responsible for more than half of the community respirat... more Prokaryote respiration is expected to be responsible for more than half of the community respiration in the ocean, but the lack of a practical method to measure the rate of prokaryote respiration in the open ocean resulted in very few published data leaving the role of organotrophic prokaryotes open to debate. Oxygen consumption rates of oceanic prokaryotes measured with current methods may be biased due to pre-incubation size filtration and long incubation times both of which can change the physiological and taxonomic profile of the sample during the incubation period. In vivo INT reduction has been used in terrestrial samples to estimate respiration rates, and recently, the method was introduced and applied in aquatic ecology. We measured oxygen consumption rates and in vivo INT reduction to formazan in cultures of marine bacterioplankton communities, Vibrio harveyi and the eukaryote Isochrysis galbana. For prokaryotes, we observed a decrease in oxygen consumption rates with increasing INT concentrations between 0.05 and 1 mM. Time series after 0.5 mM INT addition to prokaryote samples showed a burst of in vivo INT reduction to formazan and a rapid decline of oxygen consumption rates to zero within less than an hour. Our data for non-axenic eukaryote cultures suggest poisoning of the eukaryote. Prokaryotes are clearly poisoned by INT on time scales of less than 1 h, invalidating the interpretation of in vivo INT reduction to formazan as a proxy for oxygen consumption rates.

Research paper thumbnail of High-Sustained Concentrations of Organisms at Very low Oxygen Concentration Indicated by Acoustic Profiles in the Oxygen Deficit Region Off Peru

Frontiers in Marine Science, 2021

The oxygen deficient mesopelagic layer (ODL) off Peru has concentrations below 5 μmol O2 kg–1 and... more The oxygen deficient mesopelagic layer (ODL) off Peru has concentrations below 5 μmol O2 kg–1 and is delimited by a shallow upper oxycline with strong vertical gradient and a more gradual lower oxycline (lOx). Some regions show a narrow band of slightly increased oxygen concentrations within the ODL, an intermediate oxygen layer (iO2). CTD, oxygen and lowered Acoustic Doppler Current Profiler (LADCP, 300 kHz) profiles were taken on the shelf edge and outside down to mostly 2000 m. We evaluate here the acoustic volume backscatter strength of the LADCP signal representing organisms of about 5 mm size. Dominant features of the backscatter profiles were a minimum backscatter strength within the ODL, and just below the lOx a marked backscatter increase reaching a maximum at less than 3.0 μmol O2 kg–1. Below this maximum, the acoustic backscatter strength gradually decreased down to 1000 m below the lOx. The backscatter strength also increased at the iO2 in parallel to the oxygen concentr...

Research paper thumbnail of Free-rising, tethered CTD profiler: increased vertical resolution and near surface profiling

Limnology and Oceanography: Methods, 2012

ABSTRACT The formation of a diurnal thermocline at few meters depth is difficult to document beca... more ABSTRACT The formation of a diurnal thermocline at few meters depth is difficult to document because of the mixing induced by research platforms. We built a free-rising CTD-platform, including sensors for chlorophyll fluorescence, turbidity, and light, that profiles to similar to 0.4 m below the surface with better than 0.03 m resolution and at sufficient distance from the research platform to measure an undisturbed water column. The profiler, with a practical maximum depth of 100 m is controlled mechanically using sacrificial weights and a safety tether that assures easy recovery of the instrument. The design concept is easily adapted to many commercial CTD models. Off Baja California, most profiles showed temperature stratification near the surface and some profiles showed near surface chlorophyll fluorescence thin layers; these features would be difficult to observe with normal CTD profilers.

Research paper thumbnail of A non-amplified FISH protocol to identify simultaneously different bacterial groups attached to eukaryotic phytoplankton

Journal of Applied Phycology, 2014

ABSTRACT Eukaryotic phytoplankton and bacteria form complex trophic interactions in nature and cu... more ABSTRACT Eukaryotic phytoplankton and bacteria form complex trophic interactions in nature and cultures. The interaction will depend on the spatial arrangement but the architecture of these arrangements has been little investigated. Here we modified a protocol to identify and localize multiple bacterial taxa attached to phytoplankton cells in culture and natural samples, including sensitive dinoflagellates. Samples were embedded in agarose and hybridized simultaneously with different probes of distinct fluorescence properties. Embedding avoided losses or damage of host cells and preserved the attached bacteria during hybridization and washing. Embedding still allowed efficient hybridization and identification of intact host cells. After fluorescence in situ hybridization of the bacteria the phytoplankton host cells, including dinoflagellates were still intact. Digital image stacks taken with a wide field epifluorescence microscope using different excitation– emission wavelength combinations allow the location of the different bacterial groups on the host cell surface and the spatial relationship of the different bacterial groups.

Research paper thumbnail of Correction: Maintenance of Coastal Surface Blooms by Surface Temperature Stratification and Wind Drift

PLoS ONE, 2013

The following information is missing from the Funding Statement: The Mexican CONACyT funded this ... more The following information is missing from the Funding Statement: The Mexican CONACyT funded this project (CB--2008-01 106003) and provided the doctoral fellowship to MC Ruiz de la Torre.

Research paper thumbnail of Ecohab: Hyperspectral Optical Properties of Red-Tide Blooms

The goal of our project is the bio-optical characterization of dinoflagellate and other red-tide ... more The goal of our project is the bio-optical characterization of dinoflagellate and other red-tide blooms, to facilitate the optical detection and monitoring of these blooms from above the sea surface.

Research paper thumbnail of Adsorption of Dissolved Organic Matter to the Inorganic Filter Substrate and Its Implications for 14C Uptake Measurements

Applied and Environmental Microbiology, 1994

Inorganic carbon uptake rates for glass fiber-filtered samples are higher than those for membrane... more Inorganic carbon uptake rates for glass fiber-filtered samples are higher than those for membrane-filtered samples because of adsorption of dissolved organic matter to the filter substrate. Experimentally derived values for adsorption onto filters were as follows (relative units): GF/F filter, 1, quartz filter, 1.1, GF/C filter, 0.6; GN-6 Gelman filter, 0.1; Nuclepore and Poretics filter, 0.0; Anodisc filter, 0.4 to 1.9.

Research paper thumbnail of Abundance Of Coccoid Cyanobacteria, Hydrographic Parameters And The Possible Underestimation Of In Situ Chlorophyll a In The Northern Gulf Of California And The Mexican California Current

Ciencias Marinas, 2000

The abundance of coccoid cyanobacteria was counted within the euphotic zone at a station in Delfí... more The abundance of coccoid cyanobacteria was counted within the euphotic zone at a station in Delfín Basin, in the northern Gulf of California, and at a station in the California Current, off Todos Santos Bay, during 1993. The abundance of cyanobacteria at both stations was between 107 and 108 cells L–1. Comparison with other concomitantly sampled parameters, i.e., irradiance, temperature, nutrients and chlorophyll a, showed no significant correlation with the cyanobacterial abundance. The contribution of cyanobacteria to the total in situ chlorophyll a concentration was calculated using the cyanobacterial abundance, an average published value of 1.0fgChl a cell–1 and a reduced pigment extraction efficiency in cyanobacteria. Cyanobacteria contributed, in half of the cases, more than 10% and more than 4% of the total chlorophyll in Delfín Basin and the California Current, respectively. Again, this relative contribution was not related to the other concomitantly measured in situ paramet...

Research paper thumbnail of Temporal and spatial distribution of transparent exopolymer particles off the northern coast of Baja California, Mexico

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 < ...

Research paper thumbnail of Euphotic depth, irradiance attenuation and remote sensing k490 in bio-optical provinces of the gulf of california

Ciencias Marinas, 2000

Algorithms are presented using remote sensing optical depth, 1/K490, to estimate the depth of the... more Algorithms are presented using remote sensing optical depth, 1/K490, to estimate the depth of the euphotic zone and depths where spectral irradiance at 490 nm are 10%, 3%, 1% and 0.3% of incident surface value. The linear empirical models are derived using data from radiometric profiles measured at various locations in the Gulf of California during cruises in 1995, 1997 and 1998. The models apply to three geographically and temporally separate bio-optical provinces of the gulf: the northern basin, the Midriff Islands and the southern basins. Relative uncertainties of the regression models for the 1% light depths for both spectral irradiance (490 nm) and EPAR range from approximately 5% in the northern basin to 10% in the southern basins.

Research paper thumbnail of Euphotic depth, irradiance attenuation and remote sensing k490 in bio-optical provinces of the gulf of california

Ciencias Marinas, 2000

Algorithms are presented using remote sensing optical depth, 1/K490, to estimate the depth of the... more Algorithms are presented using remote sensing optical depth, 1/K490, to estimate the depth of the euphotic zone and depths where spectral irradiance at 490 nm are 10%, 3%, 1% and 0.3% of incident surface value. The linear empirical models are derived using data from radiometric profiles measured at various locations in the Gulf of California during cruises in 1995, 1997 and 1998. The models apply to three geographically and temporally separate bio-optical provinces of the gulf: the northern basin, the Midriff Islands and the southern basins. Relative uncertainties of the regression models for the 1% light depths for both spectral irradiance (490 nm) and EPAR range from approximately 5% in the northern basin to 10% in the southern basins.

Research paper thumbnail of The Vitamin B1 and B12 Required by the Marine Dinoflagellate Lingulodinium polyedrum Can be Provided by its Associated Bacterial Community in Culture

Frontiers in microbiology, 2016

In this study we established the B1 and B12 vitamin requirement of the dinoflagellate Lingulodini... more In this study we established the B1 and B12 vitamin requirement of the dinoflagellate Lingulodinium polyedrum and the vitamin supply by its associated bacterial community. In previous field studies the B1 and B12 demand of this species was suggested but not experimentally verified. When the axenic vitamin un-supplemented culture (B-ns) of L. polyedrum was inoculated with a coastal bacterial community, the dinoflagellate's vitamin growth limitation was overcome, reaching the same growth rates as the culture growing in vitamin B1B7B12-supplemented (B-s) medium. Measured B12 concentrations in the B-s and B-ns cultures were both higher than typical coastal concentrations and B12 in the B-s culture was higher than in the B-ns culture. In both B-s and B-ns cultures, the probability of dinoflagellate cells having bacteria attached to the cell surface was similar and in both cultures an average of six bacteria were attached to each dinoflagellate cell. In the B-ns culture the free bacte...

Research paper thumbnail of Carbono en ecosistemas acuáticos de México

En este libro se conjunta la información aportada por algunos de los estudiosos de los diferentes... more En este libro se conjunta la información aportada por algunos de los estudiosos de los diferentes componentes del ciclo del carbono en los sistemas acuáticos. Se presenta un panorama de lo que actualmente se conoce sobre algunos procesos biogeoquímicos relacionados con el carbono y la posible contribución de los diferentes ecosistemas al balance temporal de este elemento. Además, se pone de manifiesto la falta de conocimiento del ciclo del carbono en algunos sistemas costeros y oceánicos, así como la necesidad apremiante de realizar un mayor esfuerzo en algunos campos de la investigación en los mares mexicanos.

Research paper thumbnail of Multidisciplinary Observing in the World Ocean’s Oxygen Minimum Zone Regions: From Climate to Fish — The VOICE Initiative

Frontiers in Marine Science, 2019

Multidisciplinary ocean observing activities provide critical ocean information to satisfy ever-c... more Multidisciplinary ocean observing activities provide critical ocean information to satisfy ever-changing socioeconomic needs and require coordinated implementation. The upper oxycline (transition between high and low oxygen waters) is fundamentally important for the ecosystem structure and can be a useful proxy for multiple observing objectives connected to eastern boundary systems (EBSs) that neighbor oxygen minimum zones (OMZs). The variability of the oxycline and its impact on the ecosystem (VOICE) initiative demonstrates how societal benefits drive the need for integration and optimization of biological, biogeochemical, and physical components of regional ocean observing related to EBS. In liaison with the Global Ocean Oxygen Network,

Research paper thumbnail of Modulation of the vertical particle transfer efficiency in the oxygen minimum zone off Peru

Biogeosciences, 2018

The fate of the organic matter (OM) produced by marine life controls the major biogeochemical cyc... more The fate of the organic matter (OM) produced by marine life controls the major biogeochemical cycles of the Earth's system. The OM produced through photosynthesis is either preserved, exported towards sediments or degraded through remineralisation in the water column. The productive eastern boundary upwelling systems (EBUSs) associated with oxygen minimum zones (OMZs) would be expected to foster OM preservation due to low O 2 conditions. But their intense and diverse microbial activity should enhance OM degradation. To investigate this contradiction, sediment traps were deployed near the oxycline and in the OMZ core on an instrumented moored line off Peru. Data provided high-temporal-resolution O 2 series characterising two seasonal steady states at the upper trap: suboxic ([O 2 ] < 25 µmol kg −1) and hypoxic-oxic (15 < [O 2 ] < 160 µmol kg −1) in austral summer and winter-spring, respectively. The OMZ vertical transfer efficiency of particulate organic carbon (POC) between traps (T eff) can be classi-Published by Copernicus Publications on behalf of the European Geosciences Union.

Research paper thumbnail of Adsorption ofDissolved Organic Matter totheInorganic Filter Substrate andItsImplications for14CUptakeMeasurements

aluminum oxide, honeycomb porepattern (Anodisc), pore size, 0.2,um;(v)membrane, mixedcellulose ac... more aluminum oxide, honeycomb porepattern (Anodisc), pore size, 0.2,um;(v)membrane, mixedcellulose acetate and cellulose nitrate, GN-6(Whatman), poresize, 0.45jum; and (vi) polycarbonate Nuclepore andPoretics, black, poresize, 0.2 ,um. Thefilters werebrought into contact withtheradioactive DOM solution bytwoalternative methods: thefilter was dipped intothesolution orthefilter washeldinavacuum filtration device andthesolution wasfiltered through it. After thefilter contacted theradioactive DOM solution, thefilter wasrinsed withanonradioactive DOM solution prepared in thesamewayastheradioactive DOM solution. Thefilter was transferred toascintillation vial, 0.5mlof1N HClwasadded, andthevialwasleft toventforatleast 24h atroom temperature andcounted (Beckman LS 5000scintillation counter; Universol cocktail (ICNRadiochemicals)). Insome

Research paper thumbnail of Of The Effect Of Mesoscale Structures On The Deep Chlorophyll And Particle Maxima At The Entrance To The Gulf Of California

The entrance to the Gulf of California is characterized by the convergence of three surface water... more The entrance to the Gulf of California is characterized by the convergence of three surface water masses resulting in a complex mesoscale field. The effects of such structures on the deep chlorophyll maximum, an ubiquitous feature of many oceanic regions, is not well known. An interdisciplinary oceanographic survey was carried out in February-March 2005. The main goal was to study the effect of mesoscale eddies on the biology of an oligotrophic ocean. Several cyclonic and anticyclonic structures were found as well as a narrow and intense current jet off the coast of Baja California. Inside cyclonic/anticyclonic eddies a relative increase/decrease of both chlorophyll and dissolved oxygen concentration is clearly observed. The deep chlorophyll maximum is found positioned above the thermocline throughout the survey. Higher concentrations are found inside the deep chlorophyll maximum inside the cyclonic eddy and in the deep chlorophyll maximum of the coastal jet. The latter case is cons...

Research paper thumbnail of The Chemical Transformation of the Cellular Toxin INT (2-(4-Iodophenyl)-3-(4-Nitrophenyl)-5-(Phenyl) Tetrazolium Chloride) as an Indicator of Prior Respiratory Activity in Aquatic Bacteria

International Journal of Molecular Sciences, 2019

In the ocean, the prokaryote respiration rates dominate the oxidation of organics, but the measur... more In the ocean, the prokaryote respiration rates dominate the oxidation of organics, but the measurements may be biased due to pre-incubation size filtration and long incubation times. To overcome these difficulties, proxies for microbial respiration rates have been proposed, such as the in vitro and in vivo estimation of electron transport system rates (ETS) based on the reduction of tetrazolium salts. INT (2-(4-Iodophenyl)-3-(4-Nitrophenyl)-5-(Phenyl) Tetrazolium Chloride) is the most commonly applied tetrazolium salt, although it is toxic on time scales of less than 1 h for prokaryotes. This toxicity invalidates the interpretation of the rate of in vivo INT reduction to formazan as a proxy for oxygen consumption rates. We found that with aquatic bacteria, the amount of reduced INT (F; µmol/L formazan) showed excellent relation with the respiration rates prior to INT addition (R; O2 µmol/L/hr), using samples of natural marine microbial communities and cultures of bacteria (V. harvey...

Research paper thumbnail of INT (2-(4-Iodophenyl)-3-(4-Nitrophenyl)-5-(Phenyl) Tetrazolium Chloride) Is Toxic to Prokaryote Cells Precluding Its Use with Whole Cells as a Proxy for In Vivo Respiration

Microbial Ecology, 2015

Prokaryote respiration is expected to be responsible for more than half of the community respirat... more Prokaryote respiration is expected to be responsible for more than half of the community respiration in the ocean, but the lack of a practical method to measure the rate of prokaryote respiration in the open ocean resulted in very few published data leaving the role of organotrophic prokaryotes open to debate. Oxygen consumption rates of oceanic prokaryotes measured with current methods may be biased due to pre-incubation size filtration and long incubation times both of which can change the physiological and taxonomic profile of the sample during the incubation period. In vivo INT reduction has been used in terrestrial samples to estimate respiration rates, and recently, the method was introduced and applied in aquatic ecology. We measured oxygen consumption rates and in vivo INT reduction to formazan in cultures of marine bacterioplankton communities, Vibrio harveyi and the eukaryote Isochrysis galbana. For prokaryotes, we observed a decrease in oxygen consumption rates with increasing INT concentrations between 0.05 and 1 mM. Time series after 0.5 mM INT addition to prokaryote samples showed a burst of in vivo INT reduction to formazan and a rapid decline of oxygen consumption rates to zero within less than an hour. Our data for non-axenic eukaryote cultures suggest poisoning of the eukaryote. Prokaryotes are clearly poisoned by INT on time scales of less than 1 h, invalidating the interpretation of in vivo INT reduction to formazan as a proxy for oxygen consumption rates.

Research paper thumbnail of Substrate-Limited and -Unlimited Coastal Microbial Communities Show Different Metabolic Responses with Regard to Temperature

Frontiers in Microbiology, 2017

Bacteria are the principal consumers of dissolved organic carbon (DOC) in the ocean and predation... more Bacteria are the principal consumers of dissolved organic carbon (DOC) in the ocean and predation of bacteria makes organic carbon available to higher trophic levels. The efficiency with which bacteria convert the consumed carbon (C) into biomass (i.e., carbon growth efficiency, Y) determines their ecological as well as biogeochemical role in marine ecosystems. Yet, it is still unclear how changes in temperature will affect Y and, hence, the transfer of consumed C to higher trophic levels. Here, we experimentally investigated the effect of temperature on metabolic functions of coastal microbial communities inoculated in both nutrient-limited chemostats and nutrient-unlimited turbidostats. We inoculated chemostats and turbidostats with coastal microbial communities into seawater culture medium augmented with 20 and 100 µmol L −1 of glucose respectively and measured CO 2 production, carbon biomass and cell abundance. Chemostats were cultured between 14 and 26 • C and specific growth rates (µ) between 0.05 and 6.0 day −1 , turbidostats were cultured between 10 and 26 • C with specific growth rates ranging from 28 to 62 day −1. In chemostats under substrate limitation, which is common in the ocean, the specific respiration rate (r, day −1) showed no trend with temperature and was roughly proportional to µ, implying that carbon growth efficiency (Y) displayed no tendency with temperature. The response was very different in turbidostats under temperature-limited, nutrient-repleted growth, here µ increased with temperature but r decreased resulting in an increase of Y with temperature (Q 10 : 2.6). Comparison of our results with data from the literature on the respiration rate and cell weight of monospecific bacteria indicates that in general the literature data behaved similar to chemostat data, showing no trend in specific respiration with temperature. We conclude that respiration rates of nutrient-limited bacteria measured at a certain temperature cannot be adjusted to different temperatures with a temperature response function similar to Q 10 or Arrhenius. However, the cellular respiration rate and carbon demand rate (both: mol C cell −1 day −1) show statistically significant relations with cellular carbon content (mol C cell −1) in chemostats, turbidostats, and the literature data.

Research paper thumbnail of INT (2-(4-Iodophenyl)-3-(4-Nitrophenyl)-5-(Phenyl) Tetrazolium Chloride) Is Toxic to Prokaryote Cells Precluding Its Use with Whole Cells as a Proxy for In Vivo Respiration

Microbial Ecology, 2015

Prokaryote respiration is expected to be responsible for more than half of the community respirat... more Prokaryote respiration is expected to be responsible for more than half of the community respiration in the ocean, but the lack of a practical method to measure the rate of prokaryote respiration in the open ocean resulted in very few published data leaving the role of organotrophic prokaryotes open to debate. Oxygen consumption rates of oceanic prokaryotes measured with current methods may be biased due to pre-incubation size filtration and long incubation times both of which can change the physiological and taxonomic profile of the sample during the incubation period. In vivo INT reduction has been used in terrestrial samples to estimate respiration rates, and recently, the method was introduced and applied in aquatic ecology. We measured oxygen consumption rates and in vivo INT reduction to formazan in cultures of marine bacterioplankton communities, Vibrio harveyi and the eukaryote Isochrysis galbana. For prokaryotes, we observed a decrease in oxygen consumption rates with increasing INT concentrations between 0.05 and 1 mM. Time series after 0.5 mM INT addition to prokaryote samples showed a burst of in vivo INT reduction to formazan and a rapid decline of oxygen consumption rates to zero within less than an hour. Our data for non-axenic eukaryote cultures suggest poisoning of the eukaryote. Prokaryotes are clearly poisoned by INT on time scales of less than 1 h, invalidating the interpretation of in vivo INT reduction to formazan as a proxy for oxygen consumption rates.