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- 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.
- 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.
- Nitrogen uptake kinetics of an enteric methane inhibitor, the red seaweed Asparagopsis armataPublication . Torres, Raquel; Mata, Leonardo; Santos, Rui; Alexandre, AnaThe use of red seaweeds of the genus Asparagopsis as a feed ingredient drastically decreases the enteric methane production by ruminant livestock, thereby reducing the environmental impact of this industry. To address the world demand for Asparagopsis mass production, it is essential to understand the species nutrition. In this study, we evaluated for the first time the uptake kinetics of inorganic and organic nitrogen forms of the tetrasporophyte of Asparagopsis armata, to identify the different uptake phases (surge and internally controlled) and to reveal the species preferential nitrogen sources. The time course of nitrogen uptake rates was followed, and the preferential nitrogen sources were assessed in choice-uptake experiments through the incorporation of (15) N-labelled ammonium, nitrate and amino acids. As expected, the short-term, surge uptake rates were much higher than the stabilized internally controlled uptake rates. Ammonium was the preferred form during the internally controlled phase but surprisingly, the surge uptake rates of amino acids were much higher than those of inorganic forms. The importance of amino acids for A. armata nutrition was further supported by its internally controlled uptake rates that where higher than those of nitrate. Ammonium is, thus, the main nitrogen form for the species nutrition, but pulses of organic nitrogen may be considered in the mass production of Asparagopsis for the enteric methane inhibition of the livestock industry.
- Marine heatwaves can limit the role of surfgrasses as biofilters for wastewatersPublication . Bonet-Melià, Paula; Sandoval-Gil, Jose Miguel; Samperio-Ramos, Guillermo; Vivanco-Bercovich, Manuel; Canino-Herrera, Sergio R.; Durazo, Reginaldo; Camacho-Ibar, Víctor F.; Alexandre, AnaMarine heatwaves (MHWs) can have detrimental effects on seagrasses, but knowledge about the impacts on their ecosystem services remains scarce. This work evaluated Phyllospadix scouleri (surgrass) as a biofilter for wastewater discharges, and how warming associated with MHW may affect this ecological function. The nitrogen uptake kinetics and assimilation abilities for ammonium, nitrate, and urea were examined under two different warming scenarios (single and repeated events) simulated in a mesocosm. N-uptake kinetics were related to urban sewage discharges close to surfgrass meadows. Our results revealed that surfgrasses can serve as effective biofilters because of their high nitrogen uptake rates and above-average canopy biomass. Nonetheless, exposure to both experimental warmings resulted in a significant decline in their ability to incorporate and assimilate nitrogen. Consequently, MHWs may reduce the capacity of surfgrasses to function as nitrogen sinks and green filters for sewage waters, jeopardizing their role as Blue Nitrogen systems.
- The takeover of Thalassia testudinum by Anadyomene sp. at Biscayne Bay, USA, cannot be simply explained by competition for nitrogen and phosphorousPublication . Alexandre, Ana; Collado-Vides, Ligia; Santos, RuiApart from direct light effects, we tested whether the takeover of the seagrass Thalassia testudinum by the seaweed Anadyomene sp. in high nutrient areas of Biscayne Bay, Florida, USA, is related to a faster nutrient surge uptake capacity of the seaweed and/or a negative effect on the seagrass uptake rates. Anadyomene sp. and T. testudinum showed a similar ammonium surge uptake capacity, but the seagrass performed better than the seaweed in mixed incubations at high ammonium concentrations. T. testudinum was faster than Anadyomene sp. at taking up pulses of phosphate, but the uptake rates of the seagrass were significantly decreased in the presence of the seaweed. The takeover of T. testudinum by Anadyomene sp. at Biscayne Bay is likely dominated by light and cannot be simply explained by their single or mixed nutrient surge uptake rates, but the phosphate availability and the seagrass uptake inhibition by the seaweed may also play a key role in the process.
- High nitrogen and phosphorous acquisition by belowground parts of Caulerpa prolifera (Chlorophyta) contribute to the species' rapid spread in Ria Formosa lagoon, Southern PortugalPublication . Alexandre, Ana; Santos, RuiDespite worldwide proliferation of the genus Caulerpa and subsequent effects on benthic communities, little is known about the nutritional physiology of the Caulerpales. Here, we investigated the uptake rates of ammonium, nitrate, amino acids, and phosphate through the fronds and rhizoids + stolon, the internal translocation of nitrogen, and developed a nitrogen budget for the rapidly spreading Caulerpa prolifera in Ria Formosa lagoon, southern Portugal. Caulerpa prolifera acquired nutrients by both aboveground and belowground parts at similar rates, except nitrate, for which fronds showed 2-fold higher uptake rates. Ammonium was the preferential nitrogen source (81% of the total nitrogen acquisition), and amino acids, which accounted for a significant fraction of total N acquisition (19%), were taken up at faster rates than nitrate. Basipetal translocation of 15 N incorporated as ammonium was nearly 3-fold higher than acropetal translocation, whereas 15 N translocation as nitrate and amino acids was smaller but equal in either direction. The estimated total nitrogen acquisition by C. prolifera was 689 μmol · m-2 · h-1 , whereas the total nitrogen requirement for growth was 672 μmol · m-2 · h-1 . The uptake of ammonium and amino acids by belowground parts accounted for the larger fraction of the total nitrogen acquisition of C. prolifera and is sufficient to satisfy the species nitrogen requirements for growth. This may be one reason explaining the fast spreading of the seaweed in the bare sediments of Ria Formosa where it does not have any macrophyte competitors and the concentration of nutrients is high.
- Competition for nitrogen between the seaweed Caulerpa prolifera and the seagrass Cymodocea nodosaPublication . Alexandre, Ana; Santos, RuiThe rhizophytic seaweed Caulerpa prolifera has been expanding rapidly in the Ria Formosa lagoon, southern Portugal, taking over deeper unvegetated areas and mixing with the native seagrass Cymodocea nodosa in shallower areas. In the Ria Formosa lagoon, belowground ammonium uptake from the sediment represents the main source of nitrogen for the 2 macrophytes, except during the ammonium pulses from the sediment to the water column that are incorporated through aboveground plant parts. We examined the competition for inorganic and organic nitrogen between C. prolifera and C. nodosa through a series of N-15-ammonium and N-15-amino acid surge uptake experiments combining single-species and mixed incubations at a range of nutrient concentrations. Our results showed that C. prolifera is generally faster than C. nodosa in the acquisition of ammonium and amino acids by both above- and belowground parts, and that the uptake rates of ammonium and amino acids of one species were not affected by the presence of the other species. The exception was the amino acid uptake through the rhizoids of C. prolifera, which was slightly enhanced in the presence of C. nodosa. In this situation, the aboveground ammonium uptake becomes the main contributor to the nitrogen budget of C. nodosa but not to that of C. prolifera. When ammonium pulses are considered, C. nodosa is more competitive for nitrogen than C. prolifera. In this case, the leaf uptake of ammonium is the largest contributor to the total nitrogen (ammonium plus amino acids) budget of the seagrass. Our results showed that the different nutritional strategies of the 2 macrophytes allow their coexistence in the Ria Formosa lagoon.
- Ocean warming increases the nitrogen demand and the uptake of organic nitrogen of the globally distributed seagrass Zostera marinaPublication . Alexandre, Ana; Quintã, Raquel; Hill, Paul W.; Jones, Davey L.; Santos, RuiThe impact of global warming on the metabolic state of a species may be examined by either measuring physiological rates across a latitudinal gradient or by assessing short-term responses under experimentally controlled temperature regimes. The combination of the two approaches is seldom used but it provides valuable information on an organism's responses to temperature at broader temporal and spatial scales while allowing the isolation of temperature effects from other environmental variables. Here we used both approaches to assess the warming effects on the total acquisition of dissolved inorganic nitrogen (DIN; nitrate, ammonium) and organic N (DON; amino acids, peptides) by the globally widespread seagrass Zostera marina. DIN and DON uptake rates were measured in plants from three sites covering the species latitudinal distribution in Europe (Iceland, UK and Portugal). The responses of DIN and DON uptake rates of plants from the middle latitude (UK) to a latitudinal range of temperatures (8, 12 and 17 degrees C) were also measured. We further examined the microbial uptake of DON along the latitudinal distribution and whether temperature is the main driver of that uptake. Our results showed that warming greatly increased the total N uptake by Z. marina and also the relative contribution of DON to total N acquisition. The microbial uptake of DON increased towards warmer latitudes, and temperature was the main driver of these observations. Ocean warming will increase the nitrogen demand of Z. marina and this demand may be met by an increasing uptake of organic nitrogen forms. This indicates that Z. marina, and probably other seagrass species, can be winners under global change as nitrogen uptake capacity will not limit growth driven by increased photosynthetic assimilation of CO2.
- Urea as a key nitrogen source for the invasion of thesouthern coast of Portugal by the brown seaweedRugulopteryx okamurae (Dictyotales, Phaeophyceae)Publication . Jiménez Herrero, Javier; Alexandre, Ana; Silva, João; Santos, RuiThe invasive seaweed Rugulopteryx okamurae, native to East Asia, is spreading rapidly along the western Mediterranean and southern Portugal, severely affecting coastal biodiversity, ecosystem structure, and economic sectors such as fisheries and tourism. This study examined the nutrient up-take kinetics of R. ok amurae, including ammonium, nitrate, urea, amino acids, and phosphate, and their role in nitrogen and phosphorus budgets based on laboratory growth rates. R. ok amurae demonstrated the highest uptake for ammonium (Vmax = 57.95 μmol · g −1 DW · h −1), followed by urea (7.74 μmol · g −1DW · h −1), nitrate (5.37 μmol · g −1 DW · h −1), and amino acids (3.71 μmol · g −1DW · h −1). The species showed higher uptake affinity for urea (α = 1.8), which accounted for 70% of nitrogen uptake. Phosphate uptake was low, and total nitrogen uptake exceeded growth requirements. These findings suggest that R. okamurae relies on organic nitrogen (urea) and may guide toward effective management strategies to mitigate its spread in coastal ecosystems.