Marta M. Varela

Marta M. Varela
Instituto Español de Oceanografia | IEO · Centro Oceanográfico de A Coruña

Dr. Biology

About

89
Publications
21,353
Reads
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1,539
Citations
Additional affiliations
January 2010 - October 2016
Instituto Español de Oceanografia
Position
  • Cientifico Titular
September 2007 - December 2009
University of A Coruña
Position
  • Juan de la Cierva Researcher
June 2005 - July 2007
NIOZ Royal Netherlands Institute for Sea Research
Position
  • PostDoc Position

Publications

Publications (89)
Article
Full-text available
Microbial heterotrophic activity is a major process regulating the flux of dissolved organic matter (DOM) in the ocean, while the characteristics of this DOM strongly influence its microbial utilization and fate in the ocean. In order to broaden the vertical resolution of leucine-to-carbon conversion factors (CFs), needed for converting substrate i...
Article
Full-text available
Understanding the factors that modulate prokaryotic assemblages and their niche partitioning in marine environments is a longstanding challenge in marine microbial ecology. This study analyzes amplicon sequence variant (ASV) diversity and co-occurrence of prokaryotic (Archaea and Bacteria) communities through coastal-oceanic gradients in the NW Ibe...
Article
Ship-based time-series observations provide crucial data for understanding marine ecosystems, improving decision making in ocean and coastal management. However, only a few time series survive for more than a decade. RADIALES is one of the longest multidisciplinary programs in operation in the northern and northwestern coast of Spain. In the last 3...
Article
Full-text available
To study the response of bacteria to different size-fractions of naturally occurring dissolved organic matter (DOM), a natural prokaryotic community from North Atlantic mesopelagic waters (1000 m depth) was isolated and grown in (i) 0.1-µm filtered seawater (CONTROL), (ii) the low-molecular-weight (<1 kDa) DOM fraction (L-DOM), and (iii) the recomb...
Article
Full-text available
A 29-year-long time series (1990–2018) of phyto- and zooplankton abundance and composition is analyzed to uncover regime shifts related to climate and local oceanography variability. At least two major shifts were identified: one between 1997 and 1998, affecting zooplankton group abundance, phytoplankton species assemblages and climatic series, and...
Article
Full-text available
It remains unknown whether and to what extent marine prokaryotic communities are capable of degrading plastic in the ocean. To address this knowledge gap, we combined enrichment experiments employing low-density polyethylene (LDPE) as the sole carbon source with a comparison of bacterial communities on plastic debris in the Pacific, the North Atlan...
Article
Full-text available
OPEN ACCESS VERSION https://doi.org/10.1016/j.ecss.2020.106791 We combined flow cytometry, CARD-FISH, and 16 S rRNA gene tag pyrosequencing to investigate bacterioplankton dynamics along a transect in shelf waters off A Coruña (Galicia, NW Spain). Over five days (16–20 July 2012) we sampled a situation of summer upwelling relaxation, providing an...
Article
Full-text available
Taurine, an amino acid-like compound, acts as an osmostress protectant in many marine metazoans and algae and is released via various processes into the oceanic dissolved organic matter pool. Taurine transporters are widespread among members of the marine prokaryotic community, tentatively indicating that taurine might be an important substrate for...
Article
Full-text available
The analysis of a 28-year-long (1989–2016) series of monthly measurements of chlorophyll concentrations and primary production rates at a shelf station off A Coruña (NW Spain) provided evidence of changes at several time scales that were only partly related to upwelling intensity. Chlorophyll determinations were made in acetonic extracts and primar...
Preprint
Full-text available
Note this is a preprint. Published version available in https://link.springer.com/article/10.1007/s10236-019-01278-y The analysis of a 28 yr long (1989-2016) series of monthly measurements of chlorophyll concentrations and primary production rates at a shelf station off A Coruña (NW Spain) provided evidence of changes at several time scales that we...
Article
Full-text available
Knowledge of the ecology of N2-fixing (diazotrophic) plankton is mainly limited to oligotrophic (sub) tropical oceans. However, diazotrophs are widely distributed and active throughout the global ocean. Likewise, relatively little is known about the temporal dynamics of diazotrophs in productive areas. Between February 2014 and December 2015, we ca...
Article
The impact of grazing, resource competition and light on prokaryotic growth and taxonomic composition in subtropical and tropical surface waters was studied through 10 microcosm experiments conducted between 30°N and 30°S in the Atlantic, Pacific and Indian oceans. Under natural sunlight conditions, significant changes in taxonomic composition were...
Article
Full-text available
Analysis of seasonal patterns of marine bacterial community structure along horizontal and vertical spatial scales can help to predict long-term responses to climate change. Several recent studies have shown predictable seasonal reoccurrence of bacterial assemblages. However, only a few have assessed temporal variability over both horizontal and ve...
Article
Full-text available
The effect of inorganic nutrients on planktonic assemblages has traditionally relied on concentrations rather than estimates of nutrient supply. We combined a novel dataset of hydrographic properties, turbulent mixing, nutrient concentration, and picoplankton community composition with the aims of (i) quantifying the role of temperature, light, and...
Chapter
Las bacterias son microorganismos procariotas de un tamaño normalmente inferior a 1-2 µm que típicamente presentan forma esférica (coco), alargada (bacilo), de coma (vibrio) o espiral (espirilo). A pesar de su simplicidad morfológica, se trata de un grupo de organismos extremadamente diverso en cuanto a su taxonomía y a su función metabólica. Los o...
Preprint
Full-text available
The effect of inorganic nutrients on planktonic assemblages has been traditionally relied on concentrations rather than estimates of nutrient supply. We combined a novel dataset of hydrographic properties, turbulent mixing, nutrient concentration and picoplankton community composition with the aim of: i) quantifying the role of temperature, light a...
Article
Full-text available
The classical paradigm about marine N2 fixation establishes that this process is mainly constrained to nitrogen-poor tropical and subtropical regions, and sustained by the colonial cyanobacterium Trichodesmium spp. and diatom-diazotroph symbiosis. However, the application of molecular techniques allowed determining a high phylogenic diversity and w...
Article
Full-text available
Taurine (Tau), an amino acid-like compound, is present in almost all marine metazoans including crustacean zooplankton. It plays an important physiological role in these organisms and is released into the ambient water throughout their life cycle. However, limited information is available on the release rates by marine organisms, the concentrations...
Article
The capability of different bacterial populations to degrade abundant polymers, such as algal-derived polysaccharides, or to utilize preferentially polymers over monomers, remains largely unknown. In this study, we combined microautoradiography with fluorescence in situ hybridization (MAR-FISH) to evaluate the ability of Bacteroidetes, SAR11, Roseo...
Article
Abundance, activity and prokaryotic community composition were studied in the euphotic, intermediate and deep waters off the Galician coast (NW Iberian margin) in relation to the optical characterization of dissolved organic matter (DOM). Microbial (Archaea and Bacteria) community structure was vertically stratified. Among the Archaea, Euryarchaeot...
Article
Full-text available
The transformation of leucine incorporation into prokaryotic carbon production rates requires the use of either theoretical or empirically determined conversion factors. Empirical leucine-to-carbon conversion factors (eCFs) vary widely across environments, and little is known about their potential controlling factors. We conducted 10 surface seawat...
Conference Paper
Full-text available
Heterotrophic bacteria respond dynamically to variations in organic matter availability in the dark ocean. However, our knowledge on how the differences in sized and/or reactivity of dissolved organic matter (DOM) affect the bacterial community dynamics is still scarce. Our study aims to investigate the response of bacterial activity and community...
Article
Full-text available
We simultaneously studied microbial-mediated carbon fluxes at 2 contrasting sites within the coastal upwelling system off Galicia, near A Coruña and Vigo, Spain, over an annual cycle in order to compare the fraction of primary production released as dissolved organic carbon (DOC) and the degree of coupling between bacteria and phytoplankton. A sign...
Conference Paper
Picoplankton are the most abundant organisms in the ocean, often dominate planktonic biomass and primary production, and they could represent a substantial contribution to the global export of carbon. Nowadays, we have a limited understanding about the factors that control the picoplankton community structure. A recent analysis indicates that light...
Conference Paper
Full-text available
Recent studies suggest that the prokaryotes inhabiting the dark ocean present higher chemoautotrophic activity than assumed previously. These chemoautotrophic microbes incorporate dissolved inorganic carbon (DIC) as carbon source for biomass production and use reduced inorganic compound as an energy source. We have quantified DIC fixation in the me...
Conference Paper
Recent studies in coastal waters suggest that phytoplankton is eventually limited or colimited by some metabolites derived from bacterial activity. The majority of phytoplankton species require an exogenous source of B12 vitamin for growth. As only selected prokaryotes are able to synthesize B12, they must be the ultimate source of B12 for auxotrop...
Article
Full-text available
The dark ocean is one of the largest biomes on Earth, with critical roles in organic matter remineralization and global carbon sequestration. Despite its recognized importance, little is known about some key microbial players, such as the community of heterotrophic protists (HP), which are likely the main consumers of prokaryotic biomass. To invest...
Conference Paper
Full-text available
We have simultaneously studied the abundance, activity and prokaryotic community structure in relation to the quality of oceanic dissolved organic matter (DOM) in the meso- and bathypelagic waters off the Galician Coast (NW Spain, from 43ºN, 9ºW to 43ºN, 15ºW). Distinct water masses were identified based on their physical and chemical characteristi...
Data
Full-text available
Bacterial population distribution in the Mediter-ranean Sea has been mainly studied by considering small ge-ographical areas or specific phylogenetic groups. The present study is a molecular microbiology investigation aimed to identify the environmental factors driving total bacterio-plankton community composition of seawater samples col-lected alo...
Article
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The M84/3 cruise recently held onboard of R/V Meteor represented a great and rare opportunity for the scientific community to realize a multidisciplinary survey on the whole Mediterranean Sea. In this context, molecular microbiology investigation, realized by applying Automated Ribosomal Intergenic Sequence Analysis (ARISA) and microscope evaluatio...
Article
Marine Crenarchaeota are among the most abundant groups of prokaryotes in the ocean and recent reports suggest that they oxidize ammonia as an energy source and inorganic carbon as carbon source, while other studies indicate that Crenarchaeota use organic carbon and hence, live heterotrophically. We used catalysed reporter deposition fluorescence i...
Article
To determine the effects of Saharan dust on the abundance, biomass, community structure, and metabolic activity of oceanic microbial plankton, we conducted eight bioassay experiments between ca. 30°N and 30°S in the central Atlantic Ocean. We found that, although bulk abundance and biomass tended to remain unchanged, different groups of phytoplankt...
Article
Full-text available
We have determined the latitudinal distribution of Trichodesmium spp. abundance and community N2 fixation in the Atlantic Ocean along a meridional transect from ca. 30° N to 30° S in Novemberg-December 2007 and April-May 2008. The observations from both cruises were highly consistent in terms of absolute magnitude and latitudinal distribution, show...
Article
Full-text available
We have determined the latitudinal distribution of Trichodesmium spp. abundance and community N2 fixation in the Atlantic Ocean along a meridional transect from ca. 30° N to 30° S in November-December 2007 and April-May 2008. The observations from both cruises were highly consistent in terms of absolute magnitude and latitudinal distribution, showi...
Article
Full-text available
To determine the effects of Saharan dust on the abundance, biomass, community structure, and metabolic activity of oceanic microbial plankton, we conducted eight bioassay experiments between ca. 30uN and 30uS in the central Atlantic Ocean. We found that, although bulk abundance and biomass tended to remain unchanged, different groups of phytoplankt...
Conference Paper
Bacterioplankton significantly contribute to the global marine biogeochemical cycles, being responsible for a large fraction of the respiration and dissolved organic matter (DOM) remineralisation in the ocean. Nevertheless, little effort has been aimed at the study of the linkage between carbon processing and the structure of the bacterial communit...
Article
Full-text available
Until recently, ammonia oxidation, a key process in the global nitrogen cycle, was thought to be mediated exclusively by a few bacterial groups. It has been shown now, that also Crenarchaeota are capable to perform this initial nitrification step. The abundance of ammonia oxidizing Bacteria and Archaea was determined using the bacterial and archaea...
Article
The contribution of Chloroflexi-type SAR202 cells to total picoplankton and bacterial abundance and uptake of D- and L-aspartic acids (Asp) was determined in the different meso- and bathypelagic water masses of the (sub)tropical Atlantic (from 35 degrees N to 5 degrees S). Fluorescence in situ hybridization (FISH) revealed that the overall abundanc...
Article
The distribution and activity of the bulk picoplankton community and, using microautoradiography combined with catalysed reported deposition fluorescence in situ hybridization (MICRO-CARD-FISH), of the major prokaryotic groups (Bacteria, marine Crenarchaeota Group I and marine Euryarchaeota Group II) were determined in the water masses of the subtr...
Article
Full-text available
We used data collected at >60 stations over a 10 yr period to build the carbon budget of the plankton community in the euphotic layer of the Eastern North Atlantic Subtropical Gyre (NASE). Autotrophic biomass exceeded microbial heterotrophic biomass by a factor of 1.7. Mean (±SE), integrated chlorophyll a concentration and net particulate primary p...
Article
The variability of the percentage of extracellular dissolved organic nitrogen (DON) release (PER), along with the relationship between DON release and bacterioplankton activity, was examined during five oceanographic cruises, carried out in the upwelling region of the NW Iberian Peninsula, the SW Bay of Biscay, and a latitudinal transect in the Atl...