Browsing by Author "Vergara, Juan J."
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- Acclimation of seagrass Zostera noltii to co-occurring hydrodynamic and light stressesPublication . de los Santos, Carmen B.; Brun, Fernando G.; Bouma, Tjeerd J.; Vergara, Juan J.; Pérez-Lloréns, J. LucasSeagrasses may frequently experience a combination of velocity and light stresses, as elevated hydrodynamics often enhances turbidity and the subsequent light reduction. The objective of this study was to investigate the effects that these stressors induce on morphometric and dynamic seagrass features depending on the initial biomass partitioning. For this purpose, a factorial mesocosm experiment was conducted on plants of Zostera noltii subjected to combinations of 2 contrasting light levels (2.5 ± 0.6 and 15.6 ± 2.5 mol photons m–2 d–1) and 3 unidirectional flow velocities (0.35, 0.10 and 0.01 m s–1). No interactive effects between the 2 variables were recorded, except on plant survival and leaf length, and generally, light effects prevailed over hydrodynamic ones. Plants responded to light reduction regardless of the flow velocity treatments, showing low survival rates (which improved at high velocity), high aboveground/belowground biomass ratios (AG/BG) and a poorly developed root-rhizome system compared to plants under saturating light conditions. Plant morphometry only responded to hydrodynamic stress under saturating light: at high current velocity, plants preferentially allocated biomass into BG structures, bearing short leaves and displaying high internode and root appearance rates. Overall, light reduction promoted similar responses in plants with different AG/BG biomass ratios, but dissimilarities were recorded for current velocity. Thus, it can be concluded that, under simultaneous light and hydrodynamic stresses, light effects prevailed over hydrodynamic ones in Z. noltii, while acclimation to hydrodynamics only occurred under saturating light
- Carbon isotopic fractionation in macroalgae from Cádiz Bay (Southern Spain): comparison with other bio-geographic regionsPublication . Mercado, Jesús M.; de los Santos, Carmen B.; Pérez-Lloréns, J. Lucas; Vergara, Juan J.The 13C signature of forty-five macroalgal species from intertidal zones at Ca´diz Bay was analysed in order to research the extension of diffusive vs. non-diffusive utilisation of dissolved inorganic carbon (DIC) and to perform a comparison with data published for other bio-geographic regions. The v13C values ranged from !6.8& to !33&, although the span of variation was different depending on the taxa. Thus, v13C for Chlorophyta varied from !7& (Codium adhaerens) to !29.6& (Flabellia petiolata), while all the Phaeophyceae (excepting Padina pavonica with v13C higher than !10&) had values between !10&, and !20&. The widest variation range was recorded in Rhodophyta, from values above !10& (Liagora viscida) to values lower than !30& obtained in three species belonging to the subclass Rhodymeniophycidae. Accordingly, the mean v13C value calculated for red algae (!20.2&) was significantly lower than that for brown (!15.9&) and green algae (!15.6&). Most of the analysed red algae were species inhabiting crevices and the low intertidal fringe which explains that, on average, the shaded-habitat species had a v13C value lower than those growing fully exposed to sun (i.e. in rockpools or at the upper intertidal zone). The comparison between the capacity for non-diffusive use of DIC (i.e. active or facilitated transport of HCO3 ! and/or CO2) and the v13C values reveals that values more negative than !30& indicate that photosynthesis is dependent on CO2 diffusive entry, whereas values above this threshold would not indicate necessary the operation of a non-diffusive DIC transport mechanism. Furthermore, external carbonic anhydrase activity (extCA) and v13C values were negatively correlated indicating that the higher the dependence of the photosynthesis on the CO2 supplied from HCO3 ! via extCA, the lower the v13C in the algal material. The comparison between the v13C values obtained for the analysed species and those published for species inhabiting other bio-geographic areas (warm-temperate, cold and polar) suggests that globally (at least for the red and brown algae) the non-diffusive entry of DIC is more widely spread among the species from Ca´diz Bay than among those of polar regions. If it is assumed that nondiffusive use of DIC implies saturation of photosynthesis at the present-day CO2 concentration in seawater, our data indicate that the potential impact of the acidification on photosynthesis in the seaweed communities will be different depending on the latitude.
- Increased vulnerability of Zostera noltii to stress caused by low light and elevated ammonium levels under phosphate deficiencyPublication . Brun, Fernando G.; Olive, Irene; Malta, Erik-jan; Vergara, Juan J.; Hernandez, Ignacio; Lucas Perez-Llorens, J.The effects of light and ammonium levels on net production, fluorescence parameters and non-structural carbohydrates of the seagrass Zostera noltii under different phosphate conditions were studied. A fully factorial design was used with light (low/high levels), ammonium supply and phosphate preculture conditions of the plants as the experimental variables. Both ammonium supply and low light caused negative and synergistic effects on net production, while ammonium toxicity was more severe at high light levels; in this case, it was independent of the non-structural carbohydrate (sucrose and starch) content. Preculturing of plant with added phosphate alleviated the ammonium toxicity, and also attenuated the negative production balance of plants grown at low light levels. The results indicated that phosphate preculture ameliorated the plant's short-term response against the assayed stressors (low light, high ammonium) significantly. An overall consumption of non-structural carbohydrates in response to environmental stressors was recorded throughout the experiment, indicating the importance of carbon and phosphorus reserves to cope with adverse conditions. ln addition, phosphate deficiency increased the vulnerability of plants, which could have negative ecological consequences for seagrass species thriving under phosphate deficiency conditions, or in developing seagrass transplantation programs.
- Leaf-fracture properties correlated with nutritional traits in nine Australian seagrass species: implications for susceptibility to herbivoryPublication . de los Santos, Carmen B.; Brun, F. G.; Onoda, Yusuke; Cambridge, Marion L.; Bouma, Tjeerd J.; Vergara, Juan J.Seagrasses are exposed to the constant risk of structural damage due to abiotic factors, such as waves and currents, and biotic factors, e.g. herbivory. Leaf mechanical resistance is therefore essential in protecting plants from structural failure and may also have ecological consequences. For example, mechanical traits of seagrass leaves may play an important role in plant− herbivore interactions and food-preferences of herbivores in these ecosystems, as widely reported for terrestrial plants. However, little is known about leaf mechanical resistance against structural damage in seagrasses and how it varies with other traits such as their nutritional value. We analysed the correlation between fracture properties relevant to herbivory and the nutritional value of seagrass leaves, testing the general assumption that species that invest heavily in mechanical resistance (toughening of the leaves) will present low nitrogen and high carbon and fibre contents. Direct measurements of leaf traits were conducted on 9 seagrass species from south-western Australia: (1) leaf-fracture properties from shearing and tearing tests, (2) nutritional values (carbon to nitrogen ratio and fibre content) and (3) morphological and structural traits (specific leaf area and leaf thickness). Results showed that leaf-fracture properties in seagrasses were tightly correlated to their C:N ratio, which reflects their nutritional value, thus supporting the general assumption that C investment is inversely correlated to N content. This close correlation suggested that patterns of seagrass consumption may be influenced not only by the C:N ratio but also by the leaf-fracture properties. Among co-existing seagrasses, we found a continuous spectrum of mechanical and nutritional traits across species, which provides fundamental information about species assembly, herbivore behaviour and ecosystem functions.
- New aspect in seagrass acclimation: leaf mechanical properties vary spatially and seasonally in the temperate species Cymodocea nodosa Ucria (Ascherson)Publication . de los Santos, Carmen B.; Brun, Fernando G.; Vergara, Juan J.; Pérez-Lloréns, J. LucasSeagrasses may acclimate to environmental heterogeneity through phenotypic plasticity. In contrast to leaf morphology, which has been a central point in seagrass acclimation studies, plasticity in leaf biomechanics and fibre content is poorly understood, despite being crucial in plant ecological performance, especially regarding physical forces. We hypothesised that mechanical traits (e.g. breaking force, strength, toughness, and stiffness) and fibre content of seagrass leaves vary as morphology does under differential environments. Cymodocea nodosa was seasonally monitored at three locations around Ca´diz Bay (southern Spain) with hydrodynamic regime as the most noticeable difference between them. Leaves showed plasticity in both morphology and mechanical traits, with wave-exposed individuals presenting short but extensible and tough leaves. Leaf fibre content was invariant along the year and with little spatial variability. Cross-sectional area rather than material properties or fibre content differentiates leaf mechanical resistance. Seagrass capacity to thrive under a range of mechanical forces may be dictated by their plasticity in morpho-biomechanical traits, a key element for the hydrodynamical performance and, hence, for species colonisation and distribution.
- Recent trend reversal for declining European seagrass meadowsPublication . de los Santos, Carmen B.; Krause-Jensen, Dorte; Alcoverro, Teresa; Marbà, Nuria; Duarte, Carlos M.; Van Katwijk, Marieke; Pérez, Marta; Romero, Javier; Sánchez Lizaso, José Luis; Roca, Guillem; Jankowska, Emilia; Perez-Llorens, Jose Lucas; Fournier, Jérôme; Montefalcone, Monica; Pergent, Gérard; Ruiz, Juan M.; Cabaço, Susana; Cook, Kevan; Wilkes, Robert J.; Moy, Frithjof E.; Trayter, Gregori Muñoz-Ramos; Arañó, Xavier Seglar; Jong, Dick J. de; Fernández-Torquemada, Yolanda; Auby, Isabelle; Vergara, Juan J.; Santos, RuiSeagrass meadows, key ecosystems supporting fisheries, carbon sequestration and coastal protection, are globally threatened. In Europe, loss and recovery of seagrasses are reported, but the changes in extent and density at the continental scale remain unclear. Here we collate assessments of changes from 1869 to 2016 and show that 1/3 of European seagrass area was lost due to disease, deteriorated water quality, and coastal development, with losses peaking in the 1970s and 1980s. Since then, loss rates slowed down for most of the species and fast-growing species recovered in some locations, making the net rate of change in seagrass area experience a reversal in the 2000s, while density metrics improved or remained stable in most sites. Our results demonstrate that decline is not the generalised state among seagrasses nowadays in Europe, in contrast with global assessments, and that deceleration and reversal of declining trends is possible, expectingly bringing back the services they provide.
- Un programa de voluntariado para implicar a la sociedad en la protección de las praderas marinas en la bahía de Cádiz.Publication . Ramírez, M. Carmen; de los Santos, Carmen B.; Navarrete, Antonio; Vergara, Juan J.Las praderas de fanerógamas marinas constituyen un ecosistema de vital importancia por la enorme biodiversidad que sustentan y por proteger nuestras costas frente a la erosión. Actualmente, estas praderas submarinas sufren un declive global por el intenso efecto de la presión humana sobre las áreas costeras. La falta de transmisión del conocimiento científico hacia la población en general y el hecho de que las praderas de fanerógamas no reciben la misma atención mediática que otros temas ambientales, hacen que ni Administraciones ni usuarios de la costa conozcan la importancia de estas praderas, la problemática que presentan y el papel que ellos pueden desempeñar para su protección y conservación. En el seno de la Universidad de Cádiz y a iniciativa del grupo de investigación “Estructura y Dinámica de Ecosistemas Acuáticos” (Departamento de Biología) y la Oficina Verde, nace apenas 4 años, el programa FAMAR, un programa de voluntariado ambiental cuyo principal objetivo es el de implicar a universitarios en el seguimiento ambiental de las praderas marinas presentes en la bahía de Cádiz. Hasta este momento, FAMAR ha estado impregnado de un carácter principalmente científico. Ahora, con el objetivo de transferir este conocimiento científico, surge una nueva versión del programa a la cual denominamos “FAMAR-EA” (EA de Educación Ambiental) en la que se elaborará, con la ayuda de voluntarios, una serie de materiales divulgativos y didácticos destinados a diversos públicos. Este material se desarrollará a tres niveles: (1) Difusión general: dirigido a usuarios de las zonas donde se encuentran las praderas; (2) Difusión científico-técnica y para la gestión: dirigido a gestores ambientales y monitores de educación ambiental, así como a profesores de centros educativos; y (3) Difusión formal: destinada a distintos niveles educativos, desde primaria hasta la universidad.