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Research Project
EFFECTS OF OCEAN ACIDIFICATION ON THE NITROGEN BUDGET OF SEAGRASSES: ROLE OF ORGANIC VS. INORGANIC SOURCES
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Light is more important than nutrient ratios of fertilization for cymodocea nodosa seedling development
Publication . Alexandre, Ana; Silva, João; Santos, Rui
Restoration of seagrass beds through seedlings is an alternative to the transplantation of adult plants that reduces the impact over donor areas and increases the genetic variability of restored meadows. To improve the use of Cymodocea nodosa seedlings, obtained from seeds germinated in vitro, in restoration programs, we investigated the ammonium and phosphate uptake rates of seedlings, and the synergistic effects of light levels (20 and 200 mu mol quanta m(-2) s(-1)) and different nitrogen to phosphorus molar ratios (40 mu M N:10 mu M P, 25 mu M N:25 mu M P, and 10 mu N:40 mu M P) on the photosynthetic activity and growth of seedlings. The nutrient content of seedlings was also compared to the seed nutrient reserves to assess the relative importance of external nutrient uptake for seedling development. Eighty two percent of the seeds germinated after 48 days at a mean rate of 1.5 seeds per day. All seedlings under all treatments survived and grew during the 4 weeks of the experiment. Seedlings of C. nodosa acquired ammonium and phosphate from the incubation media while still attached to the seed, at rates of about twice of adult plants. The relevance of external nutrient uptake was further highlighted by the observation that seedlings' tissues were richer in nitrogen and phosphorus than non-germinated seeds. The uptake of ammonium followed saturation kinetics with a half saturation constant of 32 mu M whereas the uptake of phosphate increased linearly with nutrient concentration within the range tested (5 - 100 mu M). Light was more important than the nutrient ratio of fertilization for the successful development of the young seedlings. The seedlings' photosynthetic and growth rates were about 20% higher in the high light treatment, whereas different nitrogen to phosphorus ratios did not significantly affect growth. The photosynthetic responses of the seedlings to changes in the light level and their capacity to use external nutrient sources showed that seedlings of C. nodosa have the ability to rapidly acclimate to the surrounding light and nutrient environment while still attached to the seeds. C. nodosa seedlings experiencing fertilization under low light levels showed slightly enhanced growth if nourished with a balanced formulation, whereas a slight increase in growth was also observed with unbalanced formulations under a higher light level. Our results highlight the importance of high light availability at the seedling restoration sites.
First description of seagrass distribution and abundance in Sao Tome and Principe
Publication . Alexandre, Ana; Silva, João; Ferreira, Rogério; Paulo, Diogo; Serrao, Ester; Santos, Rui
Seagrass meadows in Sao Tome and Principe, eastern Atlantic Ocean, are described here for the first time. Specifically, we quantified the biomass and density of seagrasses, characterized the plant morphology and measure their nutrient content as a proxy of the nutrient environmental conditions where the meadows develop. The seagrass Halodule wrightii was found in two locations of the northeastern coast of the island of Sao Tome: 1) developing throughout an estimated area of 1500 ha surrounding Cabras islet, at a depth range of 4-10 m, on sandy bottom; and 2) at Santana bay with an area of 1500 m(2) at 5-10 m depth, on sandy bottom. A highly morphologically different population of Halodule wrightii was found on the northeastern coast of the island of Principe, off Abade beach, covering an area of 135 m2 at 4 m depth. Further research is needed to assess if this is a different species. Shoot biomass and density was 10 and 4-fold higher in Sao Tome than in Principe, respectively. CN ratios of above and belowground tissues of plants collected in Sao Tome were also significantly higher than in Principe. The carbon content of Halodule leaves from Sao Tome and Principe (41%) was much higher than that reported for other Halodule species, suggesting that meadows may have an important ecological role for carbon fixation. The presence of H. wrightii in Sao Tome and Principe raises ecological and evolutionary questions that warrant further research.
Competition for nitrogen between the seaweed Caulerpa prolifera and the seagrass Cymodocea nodosa
Publication . Alexandre, Ana; Santos, Rui
The 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.
Nitrogen uptake and internal recycling in Zostera marina exposed to oyster farming: eelgrass potential as a natural biofilter
Publication . Sandoval-Gil, José; Alexandre, Ana; Santos, Rui; Camacho-Ibar, Victor F.
Oyster farming in estuaries and coastal lagoons frequently overlaps with the distribution of seagrass meadows, yet there are few studies on how this aquaculture practice affects seagrass physiology. We compared in situ nitrogen uptake and the productivity of Zostera marina shoots growing near off-bottom longlines and at a site not affected by oyster farming in San Quintin Bay, a coastal lagoon in Baja California, Mexico. We used benthic chambers to measure leaf NH4 (+) uptake capacities by pulse labeling with (NH4)-N-15 (+) and plant photosynthesis and respiration. The internal N-15 resorption/recycling was measured in shoots 2 weeks after incubations. The natural isotopic composition of eelgrass tissues and vegetative descriptors were also examined. Plants growing at the oyster farming site showed a higher leaf NH4 (+) uptake rate (33.1 mmol NH4 (+) m(-2) day(-1)) relative to those not exposed to oyster cultures (25.6 mmol NH4 (+) m(-2) day(-1)). We calculated that an eelgrass meadow of 15-16 ha (which represents only about 3-4 % of the subtidal eelgrass meadow cover in the western arm of the lagoon) can potentially incorporate the total amount of NH4 (+) excreted by oysters (similar to 5.2 x 10(6) mmol NH4 (+) day(-1)). This highlights the potential of eelgrass to act as a natural biofilter for the NH4 (+) produced by oyster farming. Shoots exposed to oysters were more efficient in re-utilizing the internal N-15 into the growth of new leaf tissues or to translocate it to belowground tissues. Photosynthetic rates were greater in shoots exposed to oysters, which is consistent with higher NH4 (+) uptake and less negative delta C-13 values. Vegetative production (shoot size, leaf growth) was also higher in these shoots. Aboveground/belowground biomass ratio was lower in eelgrass beds not directly influenced by oyster farms, likely related to the higher investment in belowground biomass to incorporate sedimentary nutrients.
The tropical seagrass halophila stipulacea: reviewing what we know from its native and invasive habitats, alongside identifying knowledge gaps
Publication . 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, Gil
Halophila 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.
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Fundação para a Ciência e a Tecnologia
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SFRH/BPD/91629/2012