Articles

28 documents.
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Solé J., E. Berdalet, L. Arin, Ll. Cros, M. Delgado, A. Kuwata, C. Llebot, C. Marrasé
Scientia Marina, 80, S1, 33-38. DOI: 10.3989/scimar.04520.06D (BibTeX: sole.etal.2016e)
Resum: Veure
Plankton ecology has been the object of intense research and progress in the last few decades. This has been partly due to technological advances that have facilitated the multidisciplinary and high-resolution sampling of ecosystems and improved experimentation and analytical methodologies, and to sophisticated modelling. In addition, exceptional researchers have had the vision to integrate all these innovative tools to form a solid theoretical background in ecology. Here we provide an overview of the outstanding research work conducted by Professor Marta Estrada and her pioneering contribution to different areas of research in the last four decades. Her research in biological oceanography has mainly focussed on phytoplankton ecology, taxonomy and physiology, the functional structure of plankton communities, and physical and biological interactions in marine ecosystems. She has combined a variety of field and laboratory approaches and methodologies, from microscopy to satellite observations, including in-depth statistical data analysis and modelling. She has been a reference for scientists all over the world. Here, her contributions to plankton ecology are summarized by some of her students and closest collaborators, who had the privilege to share their science and everyday experiences with her.
Paraules clau: Phytoplankton ecology, taxonomy, functional structure of plankton communities, physical-biological interactions, ecología del fitoplancton, taxonomía, estructura funcional de las comunidades plantónicas, interacciones física-biología
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Romero E., F. Peters, L. Arin, J. Guillén
Journal of Sea Research, 88, 130-143. DOI: 10.1016/j.seares.2014.01.010 (BibTeX: romero.etal.2014a)
Resum: Veure
Contrary to what happens in open waters, where chlorophyll values and plankton dynamics can be predicted with a reasonable accuracy on an annual basis, biological parameters analyzed for coastal waters often show slight seasonality, and are exposed to numerous and convergent forcing factors that make it difficult to draw clear patterns. On top of this large natural variability, coastal locations subjected to urban sprawl suffer further human impact that may increase the unpredictability of plankton dynamics. Here we present the results of a multi-year time series of monthly samplings carried out in a coastal location by the city of Barcelona (NW Mediterranean) that is highly exposed to anthropogenic disturbances. Our data confirm the existence of complex patterns throughout the year. Freshwater inputs proved to be an important source of nutrients, yet the response of the planktonic organisms was vague and not systematic, contrary to the results of a previous study at a nearby coastal site less affected by human activities. The severity of anthropogenic disruptions was partially masked by the co-occurrence of natural physical phenomena, e.g., waste spills often come with downpours and large river discharge. In the NW Mediterranean, there seems to be a gradient of decreasing predictability on plankton dynamics from offshore to coastal waters with little human influence, where seasonality can be largely modified by local processes but the biological response is systematic and fairly predictable, and finally to urban coastal locations, where the seasonal background is diluted by numerous perturbations and there exists a variable pattern of biological responses. Our study underlines the importance of specific coastal processes in determining the structure and dynamics of the planktonic community, and the need to characterize coastal areas setting aside some of the assumptions valid for open ocean regions (e.g., (1) in the open ocean seasonality dominates annual nutrient fluxes, which are tightly linked to mixing and turbulence, while nutrient inputs at the coast can occur anytime throughout the year and may not be coincident with increased water-column mixing (Cloern, 1996; Cloern and Jassby, 2008); and (2) in coastal regions the concentration of nutrients during nutrient pulses can be greatly imbalanced with regard to Redfield elemental ratios (Jickells, 1998 and Justić et al., 1995 and references therein)).
Paraules clau: Plankton dynamics; Coastal areas; Anthropogenic pressure; Physical drivers; Seasonality; NW Mediterranean
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Arin L., R. Almeida, N.Sampedro, A. Reñé, D. Blasco, A. Calbet, J. Camp, M. Estrada
Harmful Algae news, 48, 14-15. (BibTeX: arin.etal.2014a)
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Arin L., J. Guillén, M. Segura-Noguera, M. Estrada
Estuarine, Coastal and Shelf Science, 133, 116-128. DOI: 10.1016/j.ecss.2013.08.018 (BibTeX: arin.etal.2013)
Resum: Veure
The dynamics of inorganic nutrients and phytoplankton was studied along two transects located in the coastal area of Barcelona (NW Mediterranean), from March 2002 to March 2006. Similar seasonal variability patterns were observed in the four annual cycles and in general, the nutrient concentrations were highest in winter and lowest in summer. Two phytoplankton peaks, composed mainly by diatoms and nanoflagellates, were generally detected during the year with the main peak during winter-early spring, linked to different fertilization mechanisms, and a secondary peak generally found in autumn, probably related both to the new availability of nutrients due to the disruption of the thermocline and to freshwater inputs. During the rest of the year, with a stratified water column and low nutrient concentrations, phytoplankton remained at a low abundance and comprised mainly small dinoflagellates, although there was smaller scale variability conditioned by rainfall events and subsequent freshwater discharges. Despite the similarity of the seasonal patterns, there were interannual changes in origin of new nutrient inputs into the coastal zone and in the taxonomic composition of the winter-early spring phytoplankton maxima. The main source of nutrients for the winter-early spring maxima of 2003 and 2004 was river runoff, while fertilization events in the two following winters were mainly due to the intrusion, onto the Barcelona shelf, of intermediate waters in 2005, and of surface offshore waters, which also carried a different phytoplankton community, in 2006. These changes were linked to unusually cold and dry weather in the winters of 2005 and 2006, which resulted in strong vertical mixing and deep water formation events in the NW Mediterranean basin. The overall amount of nutrients provided to the coastal zone by offshore water fertilization was higher (2005) or equal (2006) than that provided by freshwater inputs in 2003 and 2004. Our findings highlight the importance of identifying the different sources of nutrients in understanding the dynamics of phytoplankton and for devising management strategies of the coastal environment.
Paraules clau: inorganic nutrients; phytoplankton; coastal waters; hydrographic features; meteorology
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Almeda R., A. Calbet, M. Alcaraz, E. Saiz, I. Trepat, L. Arin, J. Movilla, V. Saló
Limnology and Oceanography, 56, 1, 415-430. DOI: 10.4319/lo.2011.56.1.0415 (BibTeX: almeda.etal.2011a)
Resum: Veure
We determined the feeding rates, trophic effect, and growth efficiencies of natural assemblages of metazoan microplankton from a coastal site in the northwest (NW) Mediterranean over a seasonal cycle in laboratory incubations. Micrometazoans, i.e., multicellular heterotrophic plankters between 20 and 200 µm, were mainly constituted by invertebrate larval stages. Copepod nauplii and copepodites dominated the community, except in April, when polychaete larvae dominated. We analyzed the grazing pressure of micrometazoans on chlorophyll a (Chl a; total and > 10 µm), nanoflagellates, phototrophic nanoflagellates, dinoflagellates, diatoms, and ciliates. Micrometazoans grazed on all the prey groups, with carbon-specific ingestion rates ranging from 0.31 to 1.24 d-1. The gross growth efficiencies for the entire metazoan microplankton community, calculated as the slope of the linear regression relating specific growth rates vs. specific ingestion rates, varied between 0.27 and 0.39. The respiratory carbon losses of micrometazoans depended on temperature and ranged from 0.16 to 0.36 d-1, with a Q10 = 2. The average net growth efficiency, 0.41, was independent of temperature and food availability. Overall micrometazoans have higher specific growth rates than, but similar food conversion efficiencies to, mesozooplankton. The grazing effect on the standing stock of the different prey was < 1% d-1 for Chl a (total and > 10 µm) and < 2.5% d-1 for the other studied prey, which seems insufficient to exert relevant control on phytoplankton and protozoan dynamics. The inclusion of micrometazoans did not change appreciably our current view of the role of metazooplankton in marine trophic webs of NW Mediterranean coastal waters.
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Peters F., L. Arin, C. Marrasé, E. Berdalet, M.M. Sala
Journal of Marine Systems, 61, 134-148. (BibTeX: peters.etal.2006b)
Resum: Veure
The effect of turbulence on the nutrient flux towards osmotrophic cells is predicted to be size dependent. This should translate into growth. We experimentally followed and modelled the growth of two marine diatoms of different size (Thalassiosira pseudonana, 6 mu m in diameter and Coscinodiscus sp., ca. 109 mu m in diameter) under still water and turbulent conditions, using a shaker table. Experiments were done with phosphorus-limited cultures and lasted for ca. 5 days. Turbulence enhanced the growth of Coscinodiscus sp. in agreement with theory but not the growth of T pseudonana, which was actually slightly lower under turbulence. At the end of the experiments there were about 1.7 times as many. Coscinodiscus sp. cells in the turbulent treatment than in the still treatment, while for T pseudonana almost the same cell concentration was found in both conditions. In addition, the Coscinodiscus sp. cells growing under still conditions presented a higher specific alkaline phosphatase activity than those growing in turbulence which indicates a higher need for phosphorus in the still cultures. A simple dynamic model, based on Michaelis-Menten nutrient uptake kinetics, needed nearly no optimisation other than using observed initial conditions of phosphate and cell concentrations. The model showed how an increased nutrient flux towards the cells translates non-linearly into cell growth, most likely by affecting the half-saturation constant (K-M). However, since Coscinodiscus sp. experienced significant mortality and cells partially settled to the bottom of the containers, unequivocal support for the size-dependent effect of turbulence on nutrient uptake will require further experiments and more sophisticated modelling. The mechanisms to connect an increased nutrient flux towards cells with population growth and whether this process is size dependent are important in parameterizing the effects of turbulence on marine plankton in coupled physical-biological models. (c) 2006 Elsevier B.V. All rights reserved.
Paraules clau: diatom growth, half saturation constant, maximum uptake velocity, nutrient uptake, phosphorus affinity, size, turbulence
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Sala M.M., V. Balagué, C. Pedrós-Alió, R. Massana, J. Felipe, L. Arin, H. Illoul, M. Estrada
FEMS Microbiology, Ecology, 54, 2, 257-267. DOI: 10.1016/j.femsec.2005.04.005 (BibTeX: sala.etal.2005)
Resum: Veure
The phylogenetic and functional diversity of the bacterioplankton assemblage associated with blooms of toxic Alexandrium spp. was studied in three harbours of the NW Mediterranean. Denaturing gradient gel electrophoresis and DNA sequence analysis revealed the presence of a bacterium within the Roseobacter clade related to the presence of Alexandrium cells. Phylogenetic diversity was affected by the presence of Alexandrium spp., geographic situation and seasonality. In contrast, functional diversity, assessed with Biolog plates, was clearly affected by seasonality, but not by the presence of Alexandrium, indicating that the presence of the bacterium associated with the blooms was not enough to modify the metabolic pattern of the bacterioplankton assemblage.
Paraules clau: Alexandrium, Bacterioplankton, Phylogenetic diversity, Functional diversity, BIOLOG, DGGE
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Arin L., M. Estrada, J. Salat, A. Cruzado
Continental Shelf Research, 25, 9, 1081-1095. DOI: 10.1016/j.csr.2004.12.011 (BibTeX: arin.etal.2005d)
Resum: Veure
The mesoscale distribution and seasonal variation of the size structure of phytoplankton biomass, as measured by chlorophyll a (chl a), was studied in the Ebro shelf area (NW Mediterranean) during three different seasons: autumn, winter and summer. In autumn and summer, when the water column was, respectively, slightly or strongly stratified and nutrient concentrations were low at surface, average total chl a values were 0.31 and 0.29 mg m-3, respectively. In winter, the intrusion of nutrients into the photic zone by intense vertical mixing and strong riverine inputs, produced an increase of the total autotrophic biomass (0.76 mg m-3). In the three seasons, the main contributor to total chl a was the picoplanktonic (<2 mi m) size fraction (42% in winter and around 60% in autumn and summer). The nanophytoplankton (2–20 mi m) contribution to total chl a showed the lowest variability amongst seasons (between 29% and 39%). The microplanktonic (>20 mi m) chl a size fraction was higher in winter (27%) than in the other seasons (less than 13%). The maximum total chl a concentrations were found at surface in winter, at depths of 40 m in autumn and between 50 and 80 m in summer. The relative contribution of the <2 mi m size fraction at these levels of the water column tended to be higher than at other depths in autumn and winter and lower in summer. In autumn and winter, nutrient inputs from Ebro river discharge and mixing processes resulted in an increase on the >2 mi m contribution to total chl a in the coastal zone near the Ebro Delta area. In summer, the contribution of the <2 and >2 mi m chl a size fractions was homogeneously distributed through the sampling area. In autumn and summer, when deep chl a maxima were observed, the total amount of the autotrophic biomass in the superficial waters (down to 10 m) of most offshore stations was less than 10% of the whole integrated chl a (down to 100 m or to the bottom). In winter, this percentage increased until 20% or 40%. The >2 mi m chl a increased linearly with total chl a values. However, the <2 mi m chl a showed a similar linear relationship only at total chl a values lower than 1mg m-3 (in autumn and summer) or 2 mg m-3 (winter). At higher values of total chl a, the contribution of the <2 mi m size fraction remained below an upper limit of roughly 0.5 mg m-3. Our results indicate that the picoplankton fraction of phytoplankton may show higher seasonal and mesoscale variability than is usually acknowledged.
Paraules clau: Spatio-temporal variation; Chlorophyll a fractionation; Picoplankton; Nanoplankton; Microplankton; Ebro river shelf; Northwestern Mediterranean.
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Estrada M., J. Salat, M. Emelianov, L. Arín, D. Blasco, A. Morales
, Rapports et Proces-verbaux des Réunions. Com. Int. Explor. Sci. Mer Mediterranée, CIESM.. Ed. CIESM. 37, 96. Montecarlo (Monaco). ISSN: 0373-434X (BibTeX: estrada.etal.2004c)
Resum: Veure
The reduction of deep mixing extent and changes in phytoplankton distributions due to an anomaly in the circulation during winter are presented and compared with a typical winter
Paraules clau: Deep mixing, phytoplankton, NW Mediterranean, marine circulation
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Sampedro N., M. Vila, L. Arin, E. Garcés, J. Camp
VIII Reunión Ibérica sobre Fitopláncton Tóxico y Biotoxinas, . Ed. Norte M, Fernández JJ (eds). Universidad de La Laguna. 29-38. (BibTeX: sampedro.etal.2004a)
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Arín Carrau L.,
PhD thesis. Director/es: M. Estrada i Miyares. (BibTeX: arincarrau.2002b)
Resum: Veure
El conocimiento de la estructura de tamaños de las comunidades de microorganismos planctónicos y de su composición química es importante debido, entre otros aspectos, a la implicación que tienen ambos en el flujo de materia y energía entre los distintos eslabones de la cadena trófica. En un ambiente determinado, el desarrollo de un tipo de red trófica depende, fundamentalmente, de los factores físico-químicos del medio. Según el esquema generalmente aceptado, en aguas ricas en nutrientes y con cierta intensidad de mezcla turbulenta, el desarrollo de autótrofos grandes haría que predominase la vía trófica "clásica" (Steele 1974), mientas que en ambientes oligotróficos y estratificados, el desarrollo de autótrofos pequeños favorecería la vía trófica "microbiana" (Azam et al. 1983). La dominancia de una vía trófica u otra determinaría, a su vez, el destino final del carbono fijado fotosintéticamente. [...]
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Arin L., C. Marrasé, M. Maar, F. Peters, M.M. Sala, M. Alcaraz
Aquatic Microbial Ecology, 29, 51-61. DOI: 10.3354/ame029051 (BibTeX: arin.etal.2002)
Resum: Veure
The response of phytoplankton and bacteria dynamics to turbulence and nutrient availability interactions was studied in natural coastal waters enclosed in 15 l microcosms. The effect of turbulence was examined under 3 different nutrient-induced conditions: nitrogen surplus (N, with initial addition of an excess of nitrogen, N:P ratio = 160), nitrogen:phosphorus ratio balanced (NP, with initial addition of nitrogen and phosphorus as Redfield ratio, N:P ratio = 16) and control (C, no nutrient addition). Turbulence (ε = 0.055 cm2 s-3) was generated by vertically oscillating grids. The experiment lasted for 8 d and samples were generally taken daily for nutrient and plankton measurements. Turbulence increased the relative importance of phytoplankton to bacteria when nutrients were added, while in the control the effect of turbulence was negligible. Turbulence also influenced the species¹ composition and the size distribution of the phytoplankton community. The relative contribution of diatoms to total phytoplankton biomass and the average cell size were higher under turbulence, particularly in N and NP treatments. The results of these experiments indicate the importance of considering the hydrodynamic conditions in studies addressing competition for nutrients among different osmotrophic organisms in plankton communities.
Paraules clau: Small-scale turbulence, Phytoplankton:bacteria relationship, Phytoplankton size distribution, Phytoplankton composition, Microcosms
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Maar M., L. Arin, R. Simó, M.M. Sala, F. Peters, C. Marrasé
Aquatic Microbial Ecology, 29, 1, 63-72. DOI: 10.3354/ame029063 (BibTeX: maar.etal.2002)
Resum: Veure
In the oligotrophic sea, phytoplankton and bacteria compete for nutrients. Turbulence changes the outcome of this competition by means of an increase in the nutrient flux to cells by the shear fields, which is cell-size dependent. This effect is insignificant for small cells such as natural bacteria. The hypothesis is that turbulence will increase the phytoplankton competition-capability for nutrients and reduce the organic matter utilisation by bacteria. Consequently, the composition of particulate organic matter should change. To test this hypothesis, we studied the response of natural plankton communities to turbulence enclosed in 15 l microcosms. We evaluated the response in terms of the ratio of heterotrophic:total biomass and the stoichiometry of particulate organic matter. Results under turbulent and still conditions were compared in 3 nutrient-induced conditions: nitrogen surplus (N, with initial addition of an excess of nitrogen, N:P ratio = 160), nitrogen:phosphorus ratio balanced (NP, with initial addition of nitrogen and phosphorus as Redfield ratio, N:P ratio = 16) and control (C, no nutrient addition). In N and NP conditions, turbulence decreased the heterotrophic:total biomass ratio up to 2-fold, and induced changes in the stoichiometry of the particulate organic matter. We found higher values of carbon:phosphorus and nitrogen:phosphorus ratios in turbulent than in still treatments. The magnitude of these responses to turbulence depended on the induced nutrient conditions. In the control microcosms, we found the maximum differences of carbon:phosphorus ratio between turbulence and still treatments. In terms of biomass, the response to turbulence was clear in the enriched conditions and insignificant in the control microcosms.
Paraules clau: Small-scale turbulence, Phosphorus, Particulate organic matter stoichiometry, Microcosms
Effects of turbulence conditions on the balance between production and respiration in marine planktonic communities (2002)
Alcaraz M., C. Marrasé, F. Peters, L. Arin, A. Malits
Marine Ecology Progress Series, 242, 63-71.
Phytoplankton size distribution and growth rates in the Alboran Sea (SW Mediterranean): short term variability (2002)
Arin L., X.A. G. Morán, M. Estrada
Journal of Plankton Research, 24, 1019-1033.
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Salat J., M.A. García, A. Cruzado, A. Palanques, L. Arín, D. Gomis, J. Guillén, A. De León, J. Puigdefàbregas, J. Sospedra, Z.R. Velásquez
Continental Shelf Research, 22, 2, 327-348. (BibTeX: salat.etal.2002a)
Resum: Veure
Among several field efforts undertaken in the framework of the EU MAST-III FANS project, three oceanographic cruises covering the Ebro shelf and slope regions (NW Mediterranean) were carried out on board R/V Garc!ıa del Cid between November 1996 and July 1997. A major aim of these three cruises was to provide insight into the seasonal variability of the distribution of physico-chemical oceanographic parameters and the shelf/slope circulation. In this paper we discuss the observed changes in the hydrographic structure, the spatial distribution of nutrients, chlorophyll and suspended particulate matter and the local circulation in relationship to the seasonal variability of the Ebro river discharge rates and the water column stratification. The added effects of mesoscale circulation structures and of the exchanges across the shelf edge are also addressed.
Paraules clau: Seasonal variations; Shelf edge dynamics; Water masses; Water exchange; Nutrients; Chlorophyll; Western Mediterranean; Ebro river shel
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Sala M.M., M. Karner, L. Arin, C. Marrasé
Aquatic Microbial Ecology, 23, 3, 301-311. DOI: 10.3354/ame023301 (BibTeX: sala.etal.2001)
Resum: Veure
Assessment of nutrient limitation in microbial populations in marine environments is an important topic. Existing methodologies generally demand long incubations in an experimental assay manipulating nutrients. We suggest a novel approach using the ratio between 2 ectoenzymatic activities, alkaline phosphatase (APA) and aminopeptidase (AMA), to evaluate nutrient limitation of microbial communities in situ. APA is used as an indication of P limitation and AMA of N limitation. The ratio bypasses the use of biomass estimations to calculate specific activities, which are error-prone and time-consuming. Our results from enrichment experiments have shown that the ratio APA:AMA increases in P-deficient treatments, and decreases after inorganic P addition. After P deficient nutrient addition (n treatments) the ratio APA:AMA increased to 90-230%, whereas following N+P balanced additions the ratio decreased to 30-70% of the initial value. These results demonstrate that this approach is easy, quick and gives a general insight into the nitrogen versus phosphorus nutrient balance of the communities without the need for biomass estimations or measurement of actual nutrient concentrations.
Paraules clau: Alkaline phosphate, Aminopeptidase, N:P ratio, Microbial community
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Morán X.A.G., I. Taupier-Letage, E. Vázquez-Dominguez, S. Ruíz, L. Arin, P. Raimbault, M. Estrada
Deep-Sea Research. Part I: Oceanographic Research Papers, 48, 2, 405-437. DOI: 10.1016/S0967-0637(00)00042-X (BibTeX: moran.etal.2001b)
Resum: Veure
The biomass and production of phytoplankton and bacterioplankton was investigated in relation to the mesoscale structures found in the Algerian Current during the ALGERS'96 cruise (October 1996). Biological determinations were carried out in three transects between 0o and 2oE aimed at crossing a so-called event, formed by a coastal anticyclonic eddy associated with an offshore cyclonic eddy to the west. The concentration of chlorophyll a (Chl) was maximum (>1.2mgm-3) within the cyclonic eddy and at the frontal zones between the Modified Atlantic Water (MAW) of the Algerian Current and the Mediterranean waters further north. Chl (total and >2 m) was significantly correlated with proxies of nutrient flux into the upper layers. Autotrophic picoplankton and heterotrophic bacterial abundance and production presented clear differences between MAW and Mediterranean water, with higher values at those stations under the influence of the Algerian Current. In general, greater differences were observed in production than in biomass variables. The photosynthetic parameters (derived from P-E relationships) and integrated primary production (range 189-645mgm-2d-1) responded greatly to the different hydrological conditions. The mesoscale phenomena inducing fertilization caused a 2 to 3-fold increase in primary production rates. The relatively high values found within the cyclonic eddy suggest that, although short-lived in comparison with anticyclonic eddies, these eddies may produce episodic increases of biological production not accounted for in previous surveys in the region.
Paraules clau: Phytoplankton; Bacteria; P-E relationships; Primary production; Bacterial production; Mesoscale; Mediterranean; Algerian basin
Seawater-atmosphere O2 exchange rates in open-top laboratory microcosms: application for continuous estimates of planktonic primary production and respiration (2001)
Alcaraz M., C. Marrasé, F. Peters, L. Arin, A. Malits
Journal of Experimental Marine Biology and Ecology, 257, 1-12.
Naupliar growth versus egg production in the calanoid copepod Centropages typicus (2000)
Calbet A., I. Trepat, L. Arin
Journal of Plankton Research, 22, 7, 1393-1402.
A comparison between glass fiber and membrane filters for the estimation of phytoplankton POC and DOC production (1999)
Morán X.A.G., J.M. Gasol, L. Arin, M. Estrada
Marine Ecology Progress Series, 187, 31-41.
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Arin L., E.E. Berdalet, C. Marrasé, M. Estrada, N. Guixa-Boixereu, J. Dolan
Journal of Plankton Research, 21, 7, 1299-1316. DOI: 10.1093/plankt/21.7.1299 (BibTeX: arin.etal.1999)
Resum: Veure
Using microscopic and biochemical approaches, the relative contribution of the main groups of pelagic microorganisms (bacteria, heterotrophic nanoflagellates, phytoplankton and ciliates) and detritus (<150m) to total particulate protein and DNA was investigated at two stations of the Catalano-Balearic Sea (NW Mediterranean) during the stratified period. The two stations, one located in the shelf break front (S) and the other in the open sea, above the central divergence zone (D), were sampled twice in early summer 1993. Both of them showed a well-developed deep chlorophyll maximum (DCM). Maximum DNA concentrations were observed close to the DCM, while protein concentrations were fairly homogeneous from the surface to 60 m depth in all samplings. In general, the microorganism distribution showed maximum concentrations at or near the DCM depths. At both stations, bacteria were the most important contributors to living particulate DNA (22.5-32.6%), while phytoplankton and heterotrophic nanoflagellates were the main contributors to living particulate protein (3.8-24.4 and 2.9-29.1%, respectively). In addition, an important amount of detrital DNA and protein was estimated to occur at both stations. Detrital DNA accounted for 23.9-42.9% of the particulate DNA, while detrital protein represented from 63.5 to 84.7% of the particulate protein. Because both protein and DNA contain nitrogen and DNA is also a phosphorus source, these results indicate that heterotrophic organisms and detrital particles play an important role in the nitrogen and phosphorus cycles in the open sea waters of the NW Mediterranean.
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Font J., The ALGERS 96 Group (L. Arín, A. Castellón, O. Chic, A. Cristóbal, M. Emelianov, Z. García, J. García, J.A. Gutiérrez, E. Isla, P. Jornet, A. Julià, O. Kheddaoui, M. Manzanera, P. Masquú, C. Millot, M. Pancorbo, M. Pitrat, D. Quintana, E. Reus, O. Rius, M.A. Rodríguez, S. Ruiz, J. Ruiz)
, Rapports et Proces-verbaux des Réunions. Com. Int. Explor. Sci. Mer Mediterranée, CIESM.. CIESM. 35, 140-141. ISSN: 0373-434X (BibTeX: font.etal.1998p)
Resum: Veure
ALGERS’96 was the first MATER (MAST 3 Mediterranean Targeted Project MTP II) campaign in the Algerian basin, carried out on board the Spanish R/V Hesperides in October 1996. A mesoscale meander of the Algerian current, developed near 1ºE, was exhaustively sampled: ADCP, CTD and SCTD/XBT profiles and transects, multibeam echosounding, dissolved oxigen, nutrients, chlorophyll, suspended particulate matter, primary production, bacterial abundance and radioactive tracers, together with satellite-tracked surface drifters and real-time remote sensing. The detailed analysis of all this interdisciplinary data set is giving, for the first time, a three-dimensional characterisation of the phenomenon and allows gaining some important answers on the coupling of physical and biological dynamics in the Algerian basin
Paraules clau: Algerian basin, circulation, density, fronts, primary production
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Peters F., C. Marrasé, J.M. Gasol, M.M. Sala, L. Arin
Marine Ecology Progress Series, 172, 293-303. DOI: 10.3354/meps172293 (BibTeX: peters.etal.1998)
Resum: Veure
We performed laboratory experiments with natural seawater communities of the Northwestern Mediterranean to test whether turbulence could affect bacterial abundance and activity. There was no direct effect of turbulence on bacteria when they were uncoupled from the remainder of the microbial community. In the presence of the microbial community, bacteria showed higher activity and maintained high abundances for a longer time under turbulence than in still water. Thus, turbulence sufficiently altered some microbial component or process in the water samples that indirectly affected bacteria. The population dynamics of bacteria and pigmented eukaryotes suggests that, under turbulence, there is a community grazing shift from smaller to larger prey sizes. This shift can be explained in terms of the advantage to protozoan predators which are able to prey on larger and more nutritious cells when the encounter rates with these cells are increased through the shear present under turbulence. The result is a higher control on phytoplankton and a relaxation of grazing on bacteria. Hence, episodic high turbulence events in coastal systems could accelerate nutrient recycling.
Paraules clau: Bacteria, Turbulence, Bacterial activity, Phototrophic pico- and nanoplankton, Grazing, Shift of preferred prey size
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Berdalet E., D. Vaqué, L. Arín, M. Estrada, M. Alcaraz, J.A. Fernández
Polar Biology, 17, 1, 31-38. DOI: 10.1007/s003000050102 (BibTeX: berdalet.etal.1997)
Resum: Veure
 The relationships between hydrography and spatial distribution of several biochemical indicators of microplankton biomass (chlorophyll, protein and ATP) were studied in an area covering the eastern part of the Bransfield Strait and the northern part of the Weddell Sea, during Antarctic summer (January 1994). Four hydrographic zones were identified: (a) the northern part of the Bransfield Strait, covered by waters of Bellings- hausen Sea origin; (b) a Weddell Sea water mass that affected most of the study area; (c) the Weddell-Scotia Confluence waters, observed north of Elephant Island; and (d) waters influenced by ice melting, found towards the southeastern part of the sampled area. The highest values of biomass indicators (chlorophyll a, ATP and protein) were found in the zones affected by ice-melting processes and in waters from the Bellingshausen Sea. The lowest values of all biochemical parameters were found in the Weddell Sea and in the Weddell-Scotia Confluence waters. A high variability in the hydrographic structure and the distribution of biochemical indicators was observed. The degree of stabilization of the water column, the depth of the upper mixed layer and the grazing pressure of herbivorous zooplankton played a major role in the development, accumulation and spatial variability of microplankton biomass.
Fara A., Berdalet, L. Arin
Journal of Phycology, 32, 6, 1074-1083. DOI: 10.1111/j.0022-3646.1996.01074.x (BibTeX: fara.etal.1996)
Resum: Veure
A fluorometric technique, based on the combination of RNase and DNase incubation with the use of thiazole orange (RNase/DNase method), was investigated to determine DNA and RNA concentrations in marine plankton. Tests were performed to optimize both RNase and DNase assay conditions. The RNase assay should be conducted at 37° C for 20 min with 0.5 μg·mL−1 of DNase-free RNase. An incubation at 25° C for 20 min with 10 units ·mL-1 of RNase-free DNase were the optimal conditions required for DNA digestion by DNase. The detection limits in terms of minimum biomass for reliable measurements of DNA and RNA were 7.5 and 10 μg of protein · (mL assay)−1, respectively. RNA and DNA concentration were estimated in oligotrophic water samples using the RNase/DNase and other available methods (e.g. a double fluorochrome method). The different techniques provided similar DNA estimations. However, the RNase/DNase method provided the highest sensitivity and a low variability for the estimation of RNA.
Paraules clau: DNA quantification; fluorometric techniques; natural plankton; phytoplankton; RNA quantification; thiazole orange
Effect of different nutrient combinations on phytoplankton development in microcosms (1996)
Estrada M., E. Berdalet, C. Marrasé, L. Arin, M.L. Mclean
In: Harmful and Toxic Algal Blooms, Intergovernamental Oceanographic Commission of UNESCO. Ed. T. Yasumoto, Y. Oshima and Y. Fukuyo (eds). 297-300.
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Berdalet ., E., C. Marrasé, M. Estrada, L. Arin, M.Maclean
Journal of Plankton Research, 18, 9, 1627-1641. DOI: 10.1093/plankt/18.9.1627 (BibTeX: .etal.1996a)
Resum: Veure
Natural plankton communities from Masnou, a locality 20 km north of Barcelona (NW Mediterranean coast), were enclosed in 30 l microcosms to test the effect of different availability of nitrogen (N) and phosphorus (P) on the biomass of the main microplankton groups, and the biochemical composition (DNA, protein and chlorophyll concentration) of microbial communities. Immediately after enclosure in microcosms, three different nutrient enrichments were performed: N-deficient, P-deficient and nutrient-balanced. N and P deficiencies affected the structure and the biochemical composition of the microbial communities. Phytoplankton assemblages showed similar temporal patterns under the three nutrient treatments, although the relative contribution of the different groups was notably affected. The lowest DNA concentration was measured in the P-deficient treatment, suggesting that P availability imposes the limits on the DNA levels in the ecosystem. The availability of N in the P-deficient microcosms allowed relatively high synthesis of chlorophyll and protein until the end of the experiment. Significantly high chlorophyll: DNA and protein: DNA ratios characterized the P-deficient treatment (where N was available) compared to the N-deficient microcosms. From the results obtained, we suggest that the protein: DNA ratios may constitute a biochemical indicator of the P versus N availability in natural ecosystems.