Browsing by Author "Brun, Fernando G."
Now showing 1 - 8 of 8
Results Per Page
Sort Options
- 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
- Biomechanical response of two fast-growing tropical seagrass species subjected to in situ shading and sediment fertilizationPublication . La Nafie, Yayu A.; de los Santos, Carmen B.; Brun, Fernando G.; Mashoreng, Supriadi; van Katwijk, Marieke M.; Bouma, Tjeerd J.Although seagrasses experience strong hydrodynamic forces, little is known about their biomechanical response in spite of the potential importance for their ecological success. We investigated how light reduction and sediment-nutrient enrichment affect biomechanical and morphological properties of two short-lived tropical seagrass species: Halophila ovalis and Halodule uninervis. A 50-day manipulative field experiment of shading and sediment-nutrient enrichment versus a natural population (control) showed that both shading and nutrient enrichment made the leaves of Halophila ovalis weaker (lower FTS) and more elastic (lower ET). As the absolute breakability of leaves (FMAX) was not affected by either of the treatments, this implies that these changes in strength and stiffness resulted from the increase in leaf dimensions under nutrient enrichment (i.e., longer, wider and thicker leaves) and shading conditions (i.e., thicker leaves). In contrast, the biomechanical properties of H. uninervis leaves were less responsive and only became more extensible under shading while their biomechanics did not change under sediment nutrient enrichment. This limited response of H. uninervis might be due to the lack of morphological response in this species since leaves only became longer under nutrient enrichment. When comparing both species across treatments under shading (after normalizing them with their controls), H. ovalis became significantly weaker compared to H. uninervis, and the latter became more extensible. Under nutrient enrichment, H. ovalis became significantly more elastic compared H. uninervis. Overall we found that (i) biomechanical properties can be affected by environmental conditions, (ii) the responses were species specific, and (iii) seagrass morphology (leaf thickness and width) affected by environmental conditions will influence seagrass biomechanical properties. Further experimental studies on seagrass biomechanics are needed as present understandings of the acclimation of these properties and the consequences for species functioning are only starting to emerge.
- A comprehensive analysis of mechanical and morphological traits in temperate and tropical seagrass speciesPublication . de los Santos, Carmen B.; Onoda, Yusuke; Vergara, J.J.; Pérez-Lloréns, J. Lucas; Bouma, Tjeerd J.; La Nafie, Yayu A.; Cambridge, Marion L.; Brun, Fernando G.Knowledge of plant mechanical traits is important in understanding how plants resist abiotic and biotic forces and in explaining ecological strategies such as leaf lifespan. To date, these traits have not been systematically evaluated in seagrasses. We analysed mechanical (breaking force and tensile strength) and associated traits (thickness, width, length, fibre content, mass area, and lifespan) of leaves in 22 seagrass species (around one-third of all known seagrass species) to examine (1) the inter-specific variation of these traits in relation to growth form and bioregions, (2) the contribution of morphology to leaf breaking force, (3) how breaking force scales to leaf dimensions, and (4) how mechanical and structural traits correlate to leaf longevity. We also compared our seagrass dataset with terrestrial plant databases to examine similarities between them. Large variation in leaf breaking force was found among seagrass species but, on average, temperate species resisted higher forces than tropical species. Variation in leaf breaking force was largely explained by differences in leaf width rather than thickness, likely due to the benefits in leaf reconfiguration and light interception. Species of large dimensions (long leaves) typically had high leaf breaking force, plausibly to tolerate the drag forces they may experience, which are proportional to the leaf area. Leaves of long-lived species typically had high mass per leaf area and fibre content and they supported high breaking forces. Compared to terrestrial plants, seagrasses are short-lived species with moderately strong fibre-reinforced leaves, which probably evolved to withstand the hydrodynamic forces occurring in the sea, and in response to other environmental factors. Overall, our analysis provides new insights into the physical performance of seagrasses in the marine environment.
- 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.
- 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.
- Sedimentary organic carbon and nitrogen sequestration across a vertical gradient on a temperate wetland seascape Including salt marshes, seagrass meadows and rhizophytic macroalgae bedsPublication . Barrena de los Santos, Carmen; Egea, Luis G.; Martins, Márcio; Santos, Rui; Masqué, Pere; Peralta, Gloria; Brun, Fernando G.; Jiménez-Ramos, RocíoCoastal wetlands are key in regulating coastal carbon and nitrogen dynamics and contribute significantly to climate change mitigation and anthropogenic nutrient reduction. We investigated organic carbon (OC) and total nitrogen (TN) stocks and burial rates at four adjacent vegetated coastal habitats across the seascape elevation gradient of Cádiz Bay (South Spain), including one species of salt marsh, two of seagrasses, and a macroalgae. OC and TN stocks in the upper 1 m sediment layer were higher at the subtidal seagrass Cymodocea nodosa (72.3 Mg OC ha−1, 8.6 Mg TN ha−1) followed by the upper intertidal salt marsh Sporobolus maritimus (66.5 Mg OC ha−1, 5.9 Mg TN ha−1), the subtidal rhizophytic macroalgae Caulerpa prolifera (62.2 Mg OC ha−1, 7.2 Mg TN ha−1), and the lower intertidal seagrass Zostera noltei (52.8 Mg OC ha−1, 5.2 Mg TN ha−1). The sedimentation rates increased from lower to higher elevation, from the intertidal salt marsh (0.24 g cm−2 y−1) to the subtidal macroalgae (0.12 g cm−2 y−1). The organic carbon burial rate was highest at the intertidal salt marsh (91 ± 31 g OC m−2 y−1), followed by the intertidal seagrass, (44 ± 15 g OC m−2 y−1), the subtidal seagrass (39 ± 6 g OC m−2 y−1), and the subtidal macroalgae (28 ± 4 g OC m−2 y−1). Total nitrogen burial rates were similar among the three lower vegetation types, ranging from 5 ± 2 to 3 ± 1 g TN m−2 y−1, and peaked at S. maritimus salt marsh with 7 ± 1 g TN m−2 y−1. The contribution of allochthonous sources to the sedimentary organic matter decreased with elevation, from 72% in C. prolifera to 33% at S. maritimus. Our results highlight the need of using habitat-specific OC and TN stocks and burial rates to improve our ability to predict OC and TN sequestration capacity of vegetated coastal habitats at the seascape level. We also demonstrated that the stocks and burial rates in C. prolifera habitats were within the range of well-accepted blue carbon ecosystems such as seagrass meadows and salt marshes.
- Sedimentary organic carbon and nitrogen stocks of intertidal seagrass meadows in a dynamic and impacted wetland: Effects of coastal infrastructure constructions and meadow establishment timePublication . Casal-Porras, Isabel; de los Santos, Carmen B.; Martins, Márcio; Santos, Rui; Pérez-Lloréns, J. Lucas; Brun, Fernando G.Seagrass meadows, through their large capacity to sequester and store organic carbon in their sediments, contribute to mitigate climatic change. However, these ecosystems have experienced large losses and degrada-tion worldwide due to anthropogenic and natural impacts and they are among the most threatened ecosystems on Earth. When a meadow is impacted, the vegetation is partial-or completely lost, and the sediment is exposed to the atmosphere or water column, resulting in the erosion and remineralisation of the carbon stored. This paper addresses the effects of the construction of coastal infrastructures on sediment properties, organic carbon, and total nitrogen stocks of intertidal seagrass meadows, as well as the size of such stocks in relation to meadow establishing time (recently and old established meadows). Three intertidal seagrass meadows impacted by coastal constructions (with 0% seagrass cover at present) and three adjacent non-impacted old-established meadows (with 100% seagrass cover at present) were studied along with an area of bare sediment and two recent-established seagrass meadows. We observed that the non-impacted areas presented 3-fold higher per-centage of mud and 1.5 times higher sedimentary organic carbon stock than impacted areas. Although the impacted area was relatively small (0.05-0.07 ha), coastal infrastructures caused a significant reduction of the sedimentary carbon stock, between 1.1 and 2.2 Mg OC, and a total loss of the carbon sequestration capacity of the impacted meadow. We also found that the organic carbon stock and total nitrogen stock of the recent -established meadow were 30% lower than those of the old-established ones, indicating that OC and TN accu-mulation within the meadows is a continuous process, which has important consequences for conservation and restoration actions. These results contribute to understanding the spatial variability of blue carbon and nitrogen stocks in coastal systems highly impacted by urban development.
- Waves and high nutrient loads jointly decrease survival and separately affect morphological and biomechanical properties in the seagrassZostera noltiiPublication . La Nafie, Yayu A.; de los Santos, Carmen B.; Brun, Fernando G.; van Katwijk, Marieke M.; Bouma, Tjeerd J.In an 8-week aquarium experiment, we investigated the interactive effects of waves (present vs. absent) and water-column nutrient level (high vs. low) on the survival, growth, morphology, and biomechanics of the seagrass, Zostera noltii. Survival was reduced when plants were exposed to both waves and high nutrient levels. Wave and nutrient interaction significantly reduced aboveground biomass and leaf lengths, whereas waves independently reduced growth rate, internode abundance, elongation, and appearance rates. Nutrient supply significantly reduced the strength of the leaves. Wave and nutrient interaction was the main driving force affecting survival and morphological properties of seagrass, whereas dynamical characteristics were independently affected by waves, and nutrient supply affected mainly biomechanical properties. In conclusion, this experiment revealed that the combination of exposure to waves and high nutrient levels was detrimental for Z. noltii, which indicates that this could be an important unexplored force involved in seagrass declines.