Browsing by Author "Beer, Sven"
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- Depth-specific fluctuations of gene expression and protein abundance modulate the photophysiology in the seagrass Posidonia oceanicaPublication . Procaccini, Gabriele; Ruocco, Miriam; Marin-Guirao, Lazaro; Dattolo, Emanuela; Brunet, Christophe; D'Esposito, Daniela; Lauritano, Chiara; Mazzuca, Silvia; Serra, Ilia Anna; Bernardo, Letizia; Piro, Amalia; Beer, Sven; Bjork, Mats; Gullström, Martin; Buapet, Pimchanok; Rasmusson, Lina M.; Felisberto, Paulo; Gobert, Sylvie; Runcie, John W.; Silva, João; Olive, Irene; Costa, Monya M.; Barrote, Isabel; Santos, RuiHere we present the results of a multiple organizational level analysis conceived to identify acclimative/adaptive strategies exhibited by the seagrass Posidonia oceanica to the daily fluctuations in the light environment, at contrasting depths. We assessed changes in photophysiological parameters, leaf respiration, pigments, and protein and mRNA expression levels. The results show that the diel oscillations of P. oceanica photophysiological and respiratory responses were related to transcripts and proteins expression of the genes involved in those processes and that there was a response asynchrony between shallow and deep plants probably caused by the strong differences in the light environment. The photochemical pathway of energy use was more effective in shallow plants due to higher light availability, but these plants needed more investment in photoprotection and photorepair, requiring higher translation and protein synthesis than deep plants. The genetic differentiation between deep and shallow stands suggests the existence of locally adapted genotypes to contrasting light environments. The depth-specific diel rhythms of photosynthetic and respiratory processes, from molecular to physiological levels, must be considered in the management and conservation of these key coastal ecosystems.
- Measuring seagrass photosynthesis: methods and applicationsPublication . Silva, João; Sharon, Yoni; Santos, Rui; Beer, SvenThis review originates from a keynote lecture given at the recent 8th Group for Aquatic Productivity (GAP) workshop held in Eilat, Israel. Here we examine the most important methodologies for photosynthetic measurements in seagrasses and evaluate their applications, advantages and disadvantages, and also point out the most relevant results. The most commonly used methodologies are based on oxygen (O(2)) evolution and chlorophyll fluorescence measurements. O(2)-based methodologies allowed for the first approaches to evaluate seagrass productivity, whereas chlorophyll a fluorescence has more recently become the choice method for in situ experiments, particularly in evaluating photosynthetic responses to light and assessing stress responses. New methodologies have also emerged, such as O(2) optodes, underwater CO(2) flux measurements, geo-acoustic inversion and the eddy correlation technique. However, these new methods still need calibration and validation. Our analysis of the literature also reveals several significant gaps in relevant topics concerning seagrass photosynthesis, namely the complete absence of studies on deep-growing populations that photosynthesise under extreme low light conditions and the uncertainties about the true degree of seagrass carbon limitation, which limits our ability to predict responses to global changes.
- Photosynthetic responses of Haalophila stipulacea to a light gradient. I. In situ energy partitioning of non-photochemical quenchingPublication . Runcie, John W.; Paulo, Diogo; Santos, Rui; Sharon, Yoni; Beer, Sven; Silva, JoãoThe quantum yield of photosystem II (phi(II), also termed Delta F/F-m' or F-v/F-m in light- or dark-acclimated plants, respectively) of the tropical seagrass Halophila stipulacea was measured in situ using modulated fluorescence techniques over diel periods at a range of depths. Photosynthetic electron transport rates (ETRs), as derived from phi(II) values at specific ambient photosynthetically available radiation (PAR) irradiances, increased in direct proportion to increasing irradiance in the morning and, at shallow sites (7 to 10 m), reached saturating rates and then declined in the afternoon with lower PAR-specific ETRs. On the other hand, plants at 32 to 33 m showed no saturation even at midday, and the percentage reduction in PAR-specific afternoon ETRs was less than that of the shallower plants. The use of an automated shutter in the measuring device enabled non-photochemical quenching due to down-regulation and basal intrinsic non-radiative decay to be distinguished. While midday values of down-regulation were lower in deeper water, basal intrinsic non-radioactive decay remained fairly constant at 30 to 40% at all depths, with more variation in shallow waters. The maximal phi(II) (i.e. F-v/F-m) reached similar values at midnight regardless of depth. H. stipulacea acclimates to the widely varying irradiances across this depth gradient by regularly modulating down-regulation-based non-photochemical quenching processes, while dissipating a large proportion of light energy through intrinsic decay regardless of depth.
- Photosynthetic responses of Halophila stipulacea to a light gradient. II. Acclimations following transplantationPublication . Sharon, Yoni; Silva, João; Santos, Rui; Runcie, John W.; Chernihovsky, Mark; Beer, SvenHalophila stipulacea is the dominant seagrass in the Gulf of Aqaba (northern Red Sea), where it grows from the intertidal to depths exceeding 50 m. Its successful growth under such a broad irradiance gradient shows either a high plasticity or is caused by longer-term adaptations to the various depths, possibly resulting in the formation of ecotypes. In April 2008 we transplanted shoots of this seagrass between the extreme depths of its distribution at the study site (8 and 33 m) in order to evaluate its acclimation potential to various irradiances. We compared photosynthetic parameters derived from light response curves generated by PAM fluorometry (so-called rapid light curves, RLC) and measured chlorophyll a and b concentrations. RLCs from the shallow (similar to 400 pmol photons m(-2) s(-1) at midday) and deep (similar to 35 pmol photons m(-2) s(-1) at midday) sites were characteristic for high- and low-light growing plants, respectively, and the transplanted seagrasses acclimated to their new environments within 6 d, at which time their RLCs resembled those of the original plants growing at the depths to which they had been transplanted, Concentrations of both chlorophyll a and b decreased or increased when the plants were transferred to high- vs. low-light environments, respectively, but the chlorophyll a:b ratios remained constant. These fast changes in photosynthetic responses and light absorption characteristics in response to changing light environments points to Halophila stipulacea as being a highly plastic seagrass with regard to irradiance, which may partly explain its abundance across a wide range of irradiances along the depth gradient that it occupies.
- The tropical seagrass halophila stipulacea: reviewing what we know from its native and invasive habitats, alongside identifying knowledge gapsPublication . Winters, Gidon; Beer, Sven; Willette, Demian A.; Viana, Inés G.; Chiquillo, Kelcie L.; Beca-Carretero, Pedro; Villamayor, Betty; Azcárate-García, Tomás; Shem-Tov, Rachamim; Mwabvu, Bridget; Migliore, Luciana; Rotini, Alice; Oscar, Michelle A.; Belmaker, Jonathan; Gamliel, Inbal; Alexandre, Ana; Engelen, Aschwin; Procaccini, Gabriele; Rilov, GilHalophila stipulacea is a small tropical seagrass, native to the Red Sea, Persian Gulf, and the Indian Ocean. It invaded the Mediterranean Sea 150 years ago as a Lessepsian migrant, but so far has remained in insulated, small populations across this basin. Surprisingly, in 2002 it was reported in the Caribbean Sea, where within less than two decades it spread to most of the Caribbean Island nations and reaching the South American continent. Unlike its invasion of Mediterranean, in the Caribbean H. stipulacea creates large, continuous populations in many areas. Reports from the Caribbean demonstrated the invasiveness of H. stipulacea by showing that it displaces local Caribbean seagrass species. The motivation for this review comes from the necessity to unify the existing knowledge on several aspects of this species in its native and invasive habitats, identify knowledge gaps and develop a critical strategy to understand its invasive capacity and implement an effective monitoring and conservation plan to mitigate its potential spread outside its native ranges. We systematically reviewed 164 studies related to H. stipulacea to create the "Halophila stipulacea database." This allowed us to evaluate the current biological, ecological, physiological, biochemical, and molecular knowledge of H. stipulacea in its native and invasive ranges. Here we (i) discuss the possible environmental conditions and plant mechanisms involved in its invasiveness, (ii) assess the impact of H. stipulacea on native seagrasses and ecosystem functions in the invaded regions, (iii) predict the ability of this species to invade European and transoceanic coastal waters, (iv) identify knowledge gaps that should be addressed to better understand the biology and ecology of this species both in its native and non-native habitats, which would improve our ability to predict H. stipulacea's potential to expand into new areas in the future. Considering the predicted climate change scenarios and exponential human pressures on coastal areas, we stress the need for coordinated global monitoring and mapping efforts that will record changes in H. stipulacea and its associated communities over time, across its native, invasive and prospective distributional ranges. This will require the involvement of biologists, ecologists, economists, modelers, managers, and local stakeholders.