Periodic Reporting for period 1 - OSMOTIC SEAGRASS (Physiological, biochemical and transcriptomic responses to salinity excess in the seagrass Posidonia oceanica provide insights of tolerance mechanisms and tools for environmental biomonitoring)
Reporting period: 2021-09-01 to 2023-08-31
Brines constitute a desalination residue of mostly a concentrated seawater that in cases can double natural salinity levels od the sea. The main objective of this project was to deepen in the knowledge of brine discharges affection on seagrasses. The project achieved: to assess the global trend of shallow Posidonia oceanica meadows on a wide spatial and temporal trend in Spain; to determine affection of a seagrass meadow submitted to a desalination discharge and other coexisting impacts; develop a risk assessment of tolerance in P. oceanica to desalination at the metabolic and physiological levels; the investigation was extended to the seagrass Zostera chilensis and the macroalgae Dyctiota dichotoma and Dyctiota kunthii; to assess the physiological, oxidative and osmoregulatory responses of P. oceanica against hypersalinity caused by brine and sea salts; test the viability of biochemical and molecular descriptors as brine-specific biomarkers in the field; unravel hypersalinity tolerance of P. oceanica by comparing metabolic and oxidative responses of shoot apical meristems and leaves and test their suitability as target organs for biomonitoring applications.
Our approach starts with the identification of brine dilution plumes from the discharges. Through the empiric data collected with a conductivity, temperature and depth meter (CTD), and followed by high throughput modelling, we can produce a multidimensional representation of dilution plumes this is essential for a later environmental diagnosis trough our developed environmental biotechnology tools. The following steps considered developing a combination of laboratory and field-based studies to ascertain on the ecosystem effects of these brine discharges using certain species as biological models. For instance, we developed a transcontinental investigation using 2 species within the genus of the brown macroalgae Dyctiota, in this case, Dyctiota dichotoma, natural from the Mediterranean Sea, and Dyctiota kunthii, native of the Pacific Coasts of Chile. In the first stage, both species were exposed to salinity increments that can be extrapolated to brine-induced influenced areas. These experiments allowed identification of specific stress responses to increased salinities, and which later were tested in the field through a novel transplantation device self-developed to place transplants of the species nearby (and according to CTD modelling) desalination discharges. Both investigations were published in 2 articles of the prestigious scientific journal Frontiers in Marine Sciences, and demonstrated low biological impacts on the 2 Dyctiota species, independent on studied ecosystem, the potential reliability of the use of species of this globally distributed genus as suitable organisms to be used for these effects around the world.
Current advances are being applied in the context of the Posidonia oceanica, key ecological and protected Mediterranean Sea seagrass species. In this regard, we gathered empirical evidence of one of the most important myths surrounding desalination effects on marine ecosystems; indeed, that brine composition beyond excess salinity (e.g. antifouling, antiscalants) may increase the negative effects. In this regard, we have conducted laboratory experiments increasing salinities with either real brine from a desalination plant and natural sea salts . Results are conclusive, and demonstrate that even if certain differences are visible at the level of cell metabolism, in terms of physiology (and extrapolable to population effects), there are no significant differences between plants subject to excess salinities caused by brines or sea salts. Moreover, and especially at the level of gene expression, these experiments have put in evidence specific responses (ei. genes encoding for cell channels for transport of ions under osmotic pressure) that have been already tested with field transplantation experiments using P. oceanica.
Current advances are being applied in the context of the Posidonia oceanica, key ecological and protected Mediterranean Sea seagrass species. In this regard, we gathered empirical evidence of one of the most important myths surrounding desalination effects on marine ecosystems; indeed, that brine composition beyond excess salinity (e.g. antifouling, antiscalants) may increase the negative effects. In this regard, we have conducted laboratory experiments increasing salinities with either real brine from a desalination plant and natural sea salts . Results are conclusive, and demonstrate that even if certain differences are visible at the level of cell metabolism, in terms of physiology (and extrapolable to population effects), there are no significant differences between plants subject to excess salinities caused by brines or sea salts. Moreover, and especially at the level of gene expression, these experiments have put in evidence specific responses (ei. genes encoding for cell channels for transport of ions under osmotic pressure) that have been already tested with field transplantation experiments using P. oceanica.
The main findings of the project and the possibilities for improvement and further development in future investigations:
- The upper limit of P. oceanica meadows in the province of Alicante has remained stable for the last 20 years according to populational descriptors.
- P. oceanica meadows submitted to multiple and cumulative impacts in the Bay of Alicante have suffered an important regression in their extension.
- Regression events in P. oceanica meadows mainly occur at local scale, due to specific disturbances and their interaction, rather than global processes.
- Results on D. dichotoma and D. kunthii under laboratory and field-mediated increased salinity experiments showed tolerance mechanisms and potential biomarkers to be incorporated into EMPs.
- Z. chilensis showed a reduction in its photochemical performance under hypersaline conditions, higher ROS production and antioxidant consumption.
- Salinity increments triggered an active transcriptomic response in Z. chilensis by upregulating genes related to osmolyte regulation and ion exclusion and ROS scavenging, however, osmotic stress could compromise this endemic plant’s physiology and survival in the long term.
- Brine effects on P. oceanica at morphometrical and metabolic scales are mainly caused by hypersalinity.
- Certain responses such as NPQmax, ASC consumption and regulation of genes such as STRK1 and CAT, were incremented in P. oceanica plants exposed to brine compared to the same hypersaline conditions reached using artificial sea salts.
- Molecular and metabolic biomarkers tested in P. oceanica have shown to be efficient and specific to brine discharges as they actively responded to brine exposure in the field and could be used to assess the contribution of this stressor where multiple environmental pressures exist.
- Molecular descriptors are proposed as early warning indicators in P. oceanica plants under brine discharge exposures with the aim of preventing further physiological damage and potential meadow regressions on the long term.
- Reactive oxygen species production and lipid peroxidation responded more to brine exposure in P. oceanica meristems compared to leaves.
- Meristems presented higher relative expression in genes related to osmoregulation and oxidative response compared to leaves, indicating a higher sensitivity to hypersalinity and an essential role in P. oceanica salinity tolerance.
- Meristems have the potential to be target organs to be sampled to detect brine affection by using metabolic biomarkers as early warning indicators and be representative of seagrass physiology and response to this environmental stressor.
- In future studies regarding brine discharges and seagrasses it is recommended: The use of descriptors from different levels of biological organization (like complete transcriptomes through RNAseq), the use of real desalination brine instead of artificial salts, natural conditions simulation when possible and the use of meristems as biomonitor organ of brine-derived stress.
The results of this project and the derived upcoming investigation will deliver a significant contribution to the field of environmental biotechnology, not only in the frame of desalination but also for the discrimination of impacts where multiple stressors are present. Indeed, this information will contribute to ensure a secure development of desalination as a non-conventional process to address global water scarcity under a sustainable and cost-effective scheme.
- The upper limit of P. oceanica meadows in the province of Alicante has remained stable for the last 20 years according to populational descriptors.
- P. oceanica meadows submitted to multiple and cumulative impacts in the Bay of Alicante have suffered an important regression in their extension.
- Regression events in P. oceanica meadows mainly occur at local scale, due to specific disturbances and their interaction, rather than global processes.
- Results on D. dichotoma and D. kunthii under laboratory and field-mediated increased salinity experiments showed tolerance mechanisms and potential biomarkers to be incorporated into EMPs.
- Z. chilensis showed a reduction in its photochemical performance under hypersaline conditions, higher ROS production and antioxidant consumption.
- Salinity increments triggered an active transcriptomic response in Z. chilensis by upregulating genes related to osmolyte regulation and ion exclusion and ROS scavenging, however, osmotic stress could compromise this endemic plant’s physiology and survival in the long term.
- Brine effects on P. oceanica at morphometrical and metabolic scales are mainly caused by hypersalinity.
- Certain responses such as NPQmax, ASC consumption and regulation of genes such as STRK1 and CAT, were incremented in P. oceanica plants exposed to brine compared to the same hypersaline conditions reached using artificial sea salts.
- Molecular and metabolic biomarkers tested in P. oceanica have shown to be efficient and specific to brine discharges as they actively responded to brine exposure in the field and could be used to assess the contribution of this stressor where multiple environmental pressures exist.
- Molecular descriptors are proposed as early warning indicators in P. oceanica plants under brine discharge exposures with the aim of preventing further physiological damage and potential meadow regressions on the long term.
- Reactive oxygen species production and lipid peroxidation responded more to brine exposure in P. oceanica meristems compared to leaves.
- Meristems presented higher relative expression in genes related to osmoregulation and oxidative response compared to leaves, indicating a higher sensitivity to hypersalinity and an essential role in P. oceanica salinity tolerance.
- Meristems have the potential to be target organs to be sampled to detect brine affection by using metabolic biomarkers as early warning indicators and be representative of seagrass physiology and response to this environmental stressor.
- In future studies regarding brine discharges and seagrasses it is recommended: The use of descriptors from different levels of biological organization (like complete transcriptomes through RNAseq), the use of real desalination brine instead of artificial salts, natural conditions simulation when possible and the use of meristems as biomonitor organ of brine-derived stress.
The results of this project and the derived upcoming investigation will deliver a significant contribution to the field of environmental biotechnology, not only in the frame of desalination but also for the discrimination of impacts where multiple stressors are present. Indeed, this information will contribute to ensure a secure development of desalination as a non-conventional process to address global water scarcity under a sustainable and cost-effective scheme.