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- Relatório Científico I: Avaliação dos ecossistemas de carbono azul em Portugal continental.Publication . Santos, Rui; Ito, Paula; de los Santos, Carmen B.Por ocasião da Conferência do Oceano das Nações Unidas, que decorreu em Lisboa em junho de 2022, a Fundação Calouste Gulbenkian lançou o projeto Gulbenkian Carbono Azul, em parceria com o Centro de Ciências do Mar (CCMAR) da Universidade do Algarve e a Associação Natureza Portugal em associação com a WWF – World Wide Fund for Nature (ANP|WWF), com o objetivo de investigar as informações disponíveis para mapear os ecossistemas marinhos e costeiros em Portugal continental que têm o potencial de sequestrar dióxido de carbono da atmosfera – os ecossistemas de carbono azul. Esta investigação científica, feita de norte a sul do país, caracteriza os ecossistemas (localização, áreas de distribuição, estado ambiental, reservas e taxas de sequestro de carbono, entre outras características) e propõe medidas adequadas de proteção e restauro.
- Monitoring bubble production in a seagrass meadow using a source of opportunityPublication . Felisberto, Paulo; Rodríguez, Orlando; Silva, João P.; Jesus, Sergio; Ferreira, Hugo Q.; Ferreira, Pedro P.; Cunha, Maria E.; de los Santos, Carmen B.; Olivé, Irene; Santos, RuiUnder high irradiance, the photosynthetic activity of dense seagrass meadows saturates the water forming oxygen bubbles. The diel cycle of bubble production peaks at mid-day, following light intensity pattern. It is well known that bubbles strongly affect the acoustic propagation, increasing signal attenuation and decreasing the effective water sound speed, noticeable at low frequencies. Thus, the diurnal variability of bubbles may show an interference pattern in the spectrograms of low frequency acoustic signals. In an experiment conducted in July 2016 at the Aquaculture Research Station of the Portuguese Institute for the Sea and Atmosphere in Olhão, Portugal, the spectrograms of low frequency (<20kHz) broadband noise produced by water pumps in a pond of 0.48ha covered by the seagrass Cymodocea nodosa showed interference patterns that can be ascribed to the variability of the sound speed in the water. Preliminary analysis suggests that the daily cycle of bubble concentration can be inferred from these interference patterns.
- Population-level effects of clam harvesting on the seagrass Zostera noltiiPublication . Cabaço, Susana; Alexandre, Ana; Santos, RuiSeagrass declines have been reported worldwide, mostly as a consequence of anthropogenic disturbance. In Ria Formosa lagoon, southern Portugal, the intertidal meadows of Zostera noltii are highly disturbed by clam harvesters. The most common technique used to collect the clams consists of digging and tilling the sediment with a modified knife with a large blade. Here we present both descriptive and experimental evidence of the negative effects of clam harvest on the Z. noltii populations of Ria Formosa. A comparison between disturbed and undisturbed meadows suggests that clam harvesting activities change the species population structure by significantly reducing shoot density and total biomass, particularly during August, when the harvest effort is higher. Experimental harvest revealed a short-term impact on shoot density, which rapidly recovered to control levels during the following month. An experimental manipulation of rhizome fragmentation revealed that plant survival is reduced only when fragmented rhizomes are left with 1 intact internode. Shoot production and rhizome elongation and production of fragmented rhizomes having 2 to 5 internodes were not significantly affected, even though growth and production were lower when only 2 internodes were left. Experimental shoot damage at different positions along the rhizome had a significant effect on plant survival, rhizome elongation, and production only when the apical shoot was removed. Our results show that clam harvest can adversely affect Z. noltii meadows of Ria Formosa while revealing a low modular integration that allows the species to rapidly recover from physical damage.
- Elevated trace elements in sediments and seagrasses at CO2 seepsPublication . Mishra, Amrit Kumar; Santos, Rui; Hall-Spencer, JasonSeagrasses often occur around shallow marine CO2 seeps, allowing assessment of trace metal accumulation. Here, we measured Cd, Cu, Hg, Ni, Pb and Zn levels at six CO2 seeps and six reference sites in the Mediterranean. Some seep sediments had elevated metal concentrations; an extreme example was Cd which was 43x more concentrated at a seep site than its corresponding reference site. Three seeps had metal levels that were predicted to adversely affect marine biota, namely Vulcano (for Hg), Ischia (for Cu) and Paleochori (for Cd and Ni). There were higher-than-sediment levels of Zn and Ni in Posidonia oceanica and of Zn in Cymodocea nodosa, particularly in roots. High levels of Cu were found in Ischia seep sediments, yet seagrass was abundant there, and the plants contained low levels of Cu. Differences in bioavailability and toxicity of trace elements helps explain why seagrasses can be abundant at some CO2 seeps but not at others.
- Effects of clam harvesting on sexual reproduction of the seagrass Zostera noltiiPublication . Alexandre, Ana; Santos, Rui; Serrão, EsterThe sexual reproduction of Zostera noltii in the Ria Formosa lagoon (southern Portugal) was assessed by quantifying the variation in both flowering effort and evolution of maturation stages during the fertile season. The effects of clam harvesting on the sexual reproduction of Z. noltii were investigated using both descriptive and experimental approaches. Meadows disturbed by clam harvesting were compared with undisturbed meadows in 2 sectors of the lagoon. In both sectors, disturbed meadows showed significantly lower vegetative shoot density and significantly higher reproductive effort. The reproductive effort in the western disturbed meadows was 2-fold higher than in undisturbed meadows, whereas in eastern disturbed meadows it was 4-fold higher. In disturbed meadows, early maturation stages were found until the end of the flowering season and higher seed production was observed. Both the negative effect of clam harvesting on Z. noltii density and the positive effect on its reproductive effort were confirmed by manipulative field experiments. Plots that were experimentally harvested during the fertile season showed significantly lower vegetative shoot density and higher reproductive effort than unharvested plots. Results suggest that Z. noltii responds to clam harvesting disturbance by both increasing its reproductive effort and extending its fertile season.
- Genetic homogeneity in the seagrass Cymodocea nodosa at its northern Atlantic limit revealed through RAPDPublication . Alberto, Filipe; Mata, Leonardo; Santos, RuiRandom amplified polymorphic DNA (RAPD) markers were used to analyse the genetic variability of the dioecious seagrass Cymodocea nodosa Ucria (Ascherson) in the Ria Formosa lagoon, Portugal, the species' northern limit in the Atlantic. Three individuals from each of 6 meadows were genotyped with 28 primers. Meadows described previously as having flower marks were compared with meadows where flowers did not occur. A single polymorphic band, specific for one meadow, was observed in a total of 177 fragments. The lack of genetic variability among meadows both with and without flower indicates that flower production is not associated with a higher level of genetic variation. The genetic homogeneity of C, nodosa in the Ria Formosa suggests a founder effect, produced by a single or a limited number of migrants composing the colonising gene pool, This hypothesis is supported by the geographic isolation from other populations as the nearest populations lie more than 300 km away from the Ria Formosa. The lack of reproductive success of C, nodosa in Ria Formosa natural park and its low genetic variability are important factors in the conservation of this species since recolonisation can only occur through vegetative growth.
- Effectiveness and consistency of a suite of descriptors to assess the ecological status of seagrass meadows (Posidonia oceanica L. Delile)Publication . Rotini, Alice; Belmonte, A.; Barrote, Isabel; Micheli, C.; Peirano, A.; Santos, Rui; Silva, JoãoThe increasing rate of human-induced environmental changes on coastal marine ecosystems has created a demand for effective descriptors, in particular for those suitable for monitoring the status of seagrass meadows. Growing evidence has supported the useful application of biochemical and genetic descriptors such as secondary metabolite synthesis, photosynthetic activity and genetic diversity. In the present study, we have investigated the effectiveness of different descriptors (traditional, biochemical and genetic) in monitoring seagrass meadow conservation status. The Posidonia oceanica meadow of Monterosso al Mare (Ligurian sea, NW Mediterranean) was subjected to the measurement of bed density, leaf biometry, total phenols, soluble protein and photosynthetic pigment content as well as to RAPD marker analysis. This suite of descriptors provided evidence of their effectiveness and convenient application as markers of the conservation status of P. oceanica and/or other seagrasses. Biochemical/genetic descriptors and those obtained by traditional methods depicted a well conserved meadow with seasonal variability and, particularly in summer, indicated a healthier condition in a portion of the bed (station C), which was in agreement with the physical and sedimentological features of the station. Our results support the usefulness of introducing biochemical and genetic approaches to seagrass monitoring programs since they are effective indicators of plant physiological stress and environmental disturbance.
- Nutrition of the seagrass Cymodocea nodosa: pulses of ammonium but not of phosphate are crucial to sustain the species growthPublication . Alexandre, Ana; Santos, RuiWe investigated the nutrient acquisition of the seagrass Cymodocea nodosa and the importance of sediment to water column nutrient pulses, which regularly occur in coastal lagoons forced by incoming flood tides. Ammonium was preferentially taken up and accounted for 60-90% of the total daily N acquisition, whereas amino acid acquisition through belowground plant parts represented the second most important source of N, accounting 8-34%. The uptake of ammonium pulses increased dramatically the daily N acquisition from 9.5 mmol m-2 day-1 to 1.33 mmol m-2 day-1 at ambient nutrient concentrations, enabling the species to meet its N demand. Roots accounted for 96% of the total phosphate acquisition, with no evidence for P limitation. The ability of seagrasses to adapt to nutrient pulses may be an overlooked nutrition strategy common to many ecosystems where nutrient availability in the water column is low but nutrient pulses occur.
- Response of key stress-related genes of the seagrass Posidonia oceanica in the vicinity of submarine volcanic ventsPublication . Lauritano, C.; Ruocco, M.; Dattolo, E.; Buia, M. C.; Silva, João; Santos, Rui; Olivé, Irene; Costa, M. M.; Procaccini, G.Submarine volcanic vents are being used as natural laboratories to assess the effects of increased ocean acidity and carbon dioxide (CO2) concentration on marine organisms and communities. However, in the vicinity of volcanic vents other factors in addition to CO2, which is the main gaseous component of the emissions, may directly or indirectly confound the biota responses to high CO2. Here we used for the first time the expression of antioxidant and stress-related genes of the seagrass Posidonia oceanica to assess the stress levels of the species. Our hypothesis is that unknown factors are causing metabolic stress that may confound the putative effects attributed to CO2 enrichment only. We analyzed the expression of 35 antioxidant and stress-related genes of P. oceanica in the vicinity of submerged volcanic vents located in the islands of Ischia and Panarea, Italy, and compared them with those from control sites away from the influence of vents. Reverse-transcription quantitative polymerase chain reaction (RT-qPCR) was used to characterize gene expression patterns. Fifty-one percent of genes analyzed showed significant expression changes. Metal detoxification genes were mostly down-regulated in relation to controls at both Ischia and Panarea, indicating that P. oceanica does not increase the synthesis of heavy metal detoxification proteins in response to the environmental conditions present at the two vents. The up-regulation of genes involved in the free radical detoxification response (e.g., CAPX, SODCP and GR) indicates that, in contrast with Ischia, P. oceanica at the Panarea site faces stressors that result in the production of reactive oxygen species, triggering antioxidant responses. In addition, heat shock proteins were also activated at Panarea and not at Ischia. These proteins are activated to adjust stress-accumulated misfolded proteins and prevent their aggregation as a response to some stressors, not necessarily high temperature. This is the first study analyzing the expression of target genes in marine plants living near natural CO2 vents. Our results call for contention to the general claim of seagrasses as "winners" in a high-CO2 world, based on observations near volcanic vents. Careful consideration of factors that are at play in natural vents sites other than CO2 and acidification is required. This study also constitutes a first step for using stress-related genes as indicators of environmental pressures in a changing ocean.
- 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.