Elisa Berdalet

Supllement Women in Oceanography: A Decade Later.-- 1 pagePeer Reviewe

Modelling the effect of vertical mixing on bottle incubations for determining in situ phytoplankton dynamics. I. Growth rates

Reliable estimates of in situ phytoplankton growth rates are central to understanding the dynamics of aquatic ecosystems. A common approach for estimating in situ growth rates is to incubate natural phytoplankton assemblages in clear bottles at fixed depths or irradiance levels and measure the change in chlorophyll a (Chl) over the incubation period (typically 24 h). Using a modelling approach, we investigate the accuracy of these Chl-based methods focussing on 2 aspects: (1) in a freely mixing surface layer, the cells are typically not in balanced growth, and with photoacclimation, changes in Chl may yield different growth rates than changes in carbon; and (2) the in vitro methods neglect any vertical movement due to turbulence and its effect on the cells' light history. The growth rates thus strongly depend on the incubation depth and are not necessarily representative of the depth-integrated in situ growth rate in the freely mixing surface layer. We employ an individual based turbulence and photosynthesis model, which also accounts for photoacclimation and photo - inhibition, to show that the in vitro Chl-based growth rate can differ both from its carbon-based in vitro equivalent and from the in situ value by up to 100%, depending on turbulence intensity, optical depth of the mixing layer, and incubation depth within the layer. We make recommendations for choosing the best depth for single-depth incubations. Furthermore we demonstrate that, if incubation bottles are being oscillated up and down through the water column, these systematic errors can be significantly reduced. In the present study, we focus on Chl-based methods only, while productivity measurements using carbon-based techniques (e.g. 14C) are discussed in Ross et al. (2011; Mar Ecol Prog Ser 435:33-45). © Inter-Research 2011

Modulation of ecdysal cyst and toxin dynamics of two Alexandrium (Dinophyceae) species under small-scale turbulence

Some dinoflagellate species have shown different physiological responses to certain turbulent conditions. Here we investigate how two levels of turbulent kinetic energy dissipation rates (epsilon = 0.4 and 27 cm(2) s(-3)) affect the PSP toxins and ecdysal cyst dynamics of two bloom forming species, Alexandrium minutum and A. catenella. The most striking responses were observed at the high epsilon generated by an orbital shaker. In the cultures of the two species shaken for more than 4 days, the cellular GTX(1+4) toxin contents were significantly lower than in the still control cultures. In A. minutum this trend was also observed in the C(1+2) toxin content. For the two species, inhibition of ecdysal cyst production occurred during the period of exposure of the cultures to stirring (4 or more days) at any time during their growth curve. Recovery of cyst abundances was always observed when turbulence stopped. When shaking persisted for more than 4 days, the net growth rate significantly decreased in A. minutum (from 0.25 +/- 0.01 day(-1) to 0.19 +/- 0.02 day(-1)) and the final cell numbers were lower (ca. 55.4%) than in the still control cultures. In A. catenella, the net growth rate was not markedly modified by turbulence although under long exposure to shaking, the cultures entered earlier in the stationary phase and the final cell numbers were significantly lower (ca. 23%) than in the control flasks. The described responses were not observed in the experiments performed at the low turbulence intensities with an orbital grid system, where the population development was favoured. In those conditions, cells appeared to escape from the zone of the influence of the grids and concentrated in calmer thin layers either at the top or at the bottom of the containers. This ecophysiological study provides new evidences about the sensitivity to high levels of small-scale turbulence by two life cycle related processes, toxin production and encystment, in dinoflagellates. This can contribute to the understanding of the dynamics of those organisms in nature

Toxic microalgae and global change : why have proliferations increased along the Mediterranean coast?

The ocean and the continent converge in a very narrow line that is, nonetheless, truly relevant to the health, leisure, and economy of our society. The Mediterranean coastline has undergone major changes over the last fifty years, which is evident in the alteration of its microalgae species. The proliferation of dinoflagellates is now common in microscopic organism communities in this ecosystem as a result of the modifications caused by humans and climate change. The increased frequency with which toxic microalgae blooms are detected has been key to raising awareness of this change

Cell cycle and cell mortality of Alexandrium minutum (Dinophyceae) under small-scale turbulence conditions

Decreased net population growth rates and cellular abundances have been observed in dinoflagellate species exposed to small-scale turbulence. Here, we investigated whether these effects were caused by alterations in the cell cycle and/or by cell mortality and, in turn, whether these two mechanisms depended on the duration of exposure to turbulence. The study was conducted on the toxic dinoflagellate Alexandrium minutum Halim, with the same experimental design and setup used in previous studies to allow direct comparison among results. A combination of microscopy and Coulter Counter measurements allowed us to detect cell mortality, based on the biovolume of broken cells and thecae. The turbulence applied during the exponential growth phase caused an immediate transitory arrest in the G2/M phase, but significant mortality did not occur. This finding suggests that high intensities of small-scale turbulence can alter the cell division, likely affecting the correct chromosome segregation during the dinomitosis. When shaking persisted for >4 d, mortality signals and presence of anomalously swollen cells appeared, hinting at the activation of mechanisms that induce programmed cell death. Our study suggests that the sensitivity of dinoflagellates to turbulence may drive these organisms to find the most favorable (calm) conditions to complete their division cycle.Postprin

Aproximación ecológica y epidemiológica para establecer la relación entre las proliferaciones de Ostreopsis cf. ovata y sus impactos sobre la salud humana

Blooms of the benthic dinoflagellate Ostreopsis have been related to sporadic acute respiratory symptoms and general malaise in people exposed to marine aerosols on some Mediterranean beaches. However, the direct link between recurrent Ostreopsis blooms and health problems has not been clearly established. In order to establish and elucidate the connection, we conducted a joint ecology and epidemiology study in an Ostreopsis hot spot. Throughout the bloom, which extended from the end of June until the end of October 2013, 81% of the human cohort that we studied experienced at least one Ostreopsis-related symptom. Paradoxically, the time when the effects were greatest was during a short time window in early August. This corresponded to the transition from the exponential growth to the stationary phase of the bloom. Negligible symptoms were reported from August to mid-October, during the stationary period of the proliferation, when O. cf. ovata maintained high concentrations of epiphytic cells. No clear patterns in the landward wind component were noted during the time when health effects were greatest. Our main hypothesis is that the irritants present in the aerosol are produced during a particular physiological phase of the Ostreopsis cells during the bloom.Las proliferaciones del dinoflagelado bentónico Ostreopsis en algunas playas del Mediterráneo se han relacionado con síntomas respiratorios agudos esporádicos y malestar general en las personas expuestas a los aerosoles marinos. Sin embargo, la relación directa entre las proliferaciones recurrentes de Ostreopsis y los problemas en la salud no ha sido claramente establecida. Con el fin de establecer esta conexión se realizó un estudio ecológico y epidemiológico conjunto en una playa afectada por dichos eventos. A lo largo de la proliferación, que se extendió desde finales de junio hasta finales de octubre de 2013, el 81% de la cohorte humana estudiada presentó al menos un síntoma relacionado con los potencialmente producidos por Ostreopsis. Paradójicamente, la mayoría de los efectos se produjeron durante un breve período de tiempo, a principios de agosto, coincidiendo con la transición de la fase de crecimiento exponencial de la proliferación a la fase estacionaria. A partir de agosto y hasta mediados de octubre, durante dicha fase estacionaria en que se mantuvieron concentraciones elevadas de O. cf. ovata, los síntomas fueron negligibles. Durante el período de tiempo con mayor afectación en la salud, no se observó un patrón claro en la componente de viento de mar hacia tierra. Nuestra hipótesis principal es que los compuestos irritantes presentes en el aerosol se producen durante una fase fisiológica particular de las células de Ostreopsis en un momento concreto de la proliferación

New methodological approach to estimate the turbulent kinetic energy dissipation rate

The length scale and the spatio-temporal variation of turbulence intensity has relevant implications on phytoplankton dynamics. Thus, it is important to estimate the relevant parameters that characterize the turbulence in the water column, such as epsilon (kinetic energy dissipation rates). One of the main objectives in this work is the characterization of the physical dynamics at scales relevant to the biology. Here we show different approaches to estimate the epsilon in the Alfacs Bay (Ebre Delta), where recurrent harmful algal bloom events occur. First, we applied the solid boundary layer theory wind velocities obtained by a nearby meteorological station. Secondly, the gradient temperature microstructure method, based on the Batchelor spectrum adjustment was applied on temperature data obtained by a Self-Contained Autonomous MicroProfiler (SCAMP). These two approaches have methodological restrictions, i.e. isotropic turbulent or the process applied to do the Batchelor spectrum fitting. A new method to characterize the turbulence is proposed. The velocity fields measured by a deployed high resolution 2 MHz acoustic Doppler current profiler were processed using the Reynolds decomposition to obtain an empirical parameter which provides us the information about the turbulent kinetic energy in the water column.Peer Reviewe

Respiration predicted from an Enzyme Kinetic Model and the Metabolic Theory of Ecology in two species of marine bacteria

12 pages, 8 figures, 5 tablesRespiratory oxygen consumption is the result of a cell's biochemistry. It is caused by enzymatic activity of the respiratory electron transfer system (ETS). However, in spite of this understanding, respiration models continue to be based on allometric equations relating respiration to body size, body surface, or biomass. The Metabolic Theory of Ecology (MTE) is a current example. It is based on Kleiber's law relating respiration (R) and biomass (M) in the form, View the MathML source, where C is a constant, Ea is the Arrhenius activation energy, k is the Boltzmann constant for an atom or molecule, and T is the temperature in Kelvin. This law holds because biomass packages the ETS. In contrast, we bypass biomass and model respiration directly from its causal relationship with the ETS activity, R = f (ETS). We use a biochemical Enzyme Kinetic Model (EKM) of respiratory oxygen consumption based on the substrate control of the ETS. It postulates that the upper limit of R is set by the maximum velocity, Vmax, of complex I of the ETS and the temperature, and that the substrate availability, S, modulates R between zero and this upper limit. Kinetics of this thermal-substrate regulation is described by the Arrhenius and Michaelis–Menten equations. The EKM equation takes the form View the MathML source where Rg is the molar gas constant and K is the Michaelis–Menten constant. Here, we apply the EKM and the MTE to predict a respiration time-profile throughout the exponential, steady state, and nutrient-limited phases of the marine bacteria Pseudomonas nautica and Vibrio natriegens in acetate-based cultures. Both models were tested by comparing their output with the measured RO2 time-profile. The MTE predicted respiration accurately only in the exponential growth phase, but not during the nutrient limitation part of the stationary phase. In contrast, the EKM worked well throughout both physiological phases as long as the modeled substrates fall with the declining carbon source. Results support the theoretical bases of the EKM. We conclude that the EKM holds promise for predicting respiration at the different physiological states and time-scales important to microbiological studiesFinancial support was provided by the Universidad de Las Palmas de Gran Canaria (ULPGC), the Spanish Ministry of Education and Science, the Graduate Program in Oceanography at the ULPGC, ICM-CSIC, and the research grants MODIVUS (CTM2005-04795/MAR), EXOME (CTM 2008-01616), and OITHONA (CTM2007-60052). T. Packard was supported by contract EXMAR SE-539 10/17 (Proyecto Estructurante en Ciencias Marinas). This is contribution #200906 from the Bigelow Laboratory for Ocean SciencesPeer reviewe

SCOR-IOC Global Ecology and Oceanography of Harmful Algal Blooms (GEOHAB) Program: Progress Report 2013-2015

Presentación para la reunión del Intergovernmental Panel on Harmful Algal Bloom coordinado por Global Ecology and Oceanography of Harmful Algal Blooms (GEOHAB).-- 26 pagesPeer Reviewe

Small-scale turbulence can reduce parasite infectivity to dinoflagellates

mall-scale turbulence and parasite infection are 2 important factors that govern the dynamics and fate of phytoplankton populations. We experimentally investigated the influence of turbulent mixing on the infectivity of the parasite Parvilucifera sinerae to dinoflagellates. Natural phytoplankton communities were collected during 3 stages of a bloom event in Arenys de Mar Har- bour (NW Mediterranean). The 15 to 60 μm size fraction was used as the inoculum and distributed into spherical flasks. Half of the recipients were exposed to turbulence while the rest were kept still. In the experiments, the dinoflagellate assemblage was mainly composed of Prorocentrum micans, Scrippsiella trochoidea and Alexandrium minutum. We observed a collapse of A. minutum and S. tro- choidea populations in the unshaken flasks, which coincided with an increase in parasite infectivity. After a short exposure to turbulence, the development of the dinoflagellate populations slowed down and stabilised as expected. In the shaken treatments, the infectivity was lower and the decay in the host cells numbers was delayed compared to the still treatments. The degree of interference of the turbulence with infectivity varied among the experiments, due to differences in cell abundances and possibly their physiological state. Results from a numerical model suggest that turbulence could lead to a 25 to 30% decrease in the maximum infection rate, which could be due to host population disper- sion and/or reduced host–parasite contact times. Turbulence may thus be effective in delaying the initial infection, but not in preventing it.Postprin