The Experts below are selected from a list of 1425 Experts worldwide ranked by ideXlab platform
David B. Parrish - One of the best experts on this subject based on the ideXlab platform.
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Impacts of Varying Estuarine Temperature and Light Conditions on Zostera marina (Eelgrass) and its Interactions With Ruppia Maritima (Widgeongrass)
Estuaries and Coasts, 2014Co-Authors: Kenneth A. Moore, Erin C. Shields, David B. ParrishAbstract:Seagrass populations have been declining globally, with changes attributed to anthropogenic stresses and, more recently, negative effects of global climate change. We examined the distribution of Zostera marina (eelgrass) dominated beds in the York River, Chesapeake Bay, VA over an 8-year time period. Using a temperature-dependent light model, declines in upriver areas were associated with higher light attenuation, resulting in lower light availability relative to compensating light requirements of Z . marina compared with downriver areas. An inverse relationship was observed between SAV growth and temperature with a change between net bed cover increases and decreases for the period of 2004–2011 observed at approximately 23 °C. Z . marina -dominated beds in the lower river have been recovering from a die-off event in 2005 and experienced another near complete decline in 2010, losing an average of 97 % of coverage of Z . marina from June to October. These 2010 declines were attributed to an early summer heat event in which daily mean water temperatures increased from 25 to 30 °C over a 2-week time period, considerably higher than previous years when complete die-offs were not observed. Z . marina recovery from this event was minimal, while Ruppia Maritima (widgeongrass) expanded its abundance. Water temperatures are projected to continue to increase in the Chesapeake Bay and elsewhere. These results suggest that short-term exposures to rapidly increasing temperatures by 4–5 °C above normal during summer months can result in widespread diebacks that may lead to Z . marina extirpation from historically vegetated areas, with the potential replacement by other species.
Erik Kristensen - One of the best experts on this subject based on the ideXlab platform.
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Rhizosphere O2 dynamics in young Zostera marina and Ruppia Maritima
Marine Ecology Progress Series, 2015Co-Authors: Zeljko Jovanovic, M. Pedersen, Morten Larsen, Erik Kristensen, Ronnie N. GludAbstract:Zostera marina and Ruppia Maritima often share the same habitat, but R. Maritima appears more resistant to environmental stress. We investigated the impact of light intensity and water column O2 concentrations on radial oxygen loss (ROL), in young specimens of Z. marina and R. Maritima. Planar optode imaging revealed that ROL of Z. marina was localized to the root tip, while R. Maritima showed ROL along extensive root sections. The total root biomass of the 2 spe- cies was similar, but, while R. Maritima had only 1 root, of which 33% of its length showed ROL, Z. marina had 2 to 5 individual roots, where only 2 to 3 exhibited O2 leakage, but then only at root tips. ROL resulted in an oxic volume of 4.26 ± 0.51 mm 3 plant �1 for Z. marina and 5.39 ± 0.47 mm 3 plant �1 for R. Maritima (n = 3). ROL per plant at light saturation was 2.32 ± 0.30 and 2.89 ± 0.38 nmol h �1 for Z. marina and R. Maritima, respectively. These values declined by 71 and 60% in darkness. However, both species were able to maintain ROL as long as ambient O2 levels remained >50% air saturation. The calculated ROL integrated over a 24 h cycle was 48.8 ± 10.6 nmol O2 plant �1 d �1 (n = 3) for R. Maritima and 30% less for Z. marina. The ability of R. mar- itima to maintain higher ROL than Z. marina could be an important feature defining its potential for colonizing and maintaining growth in eutrophic sediments.
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Sensitivity of Ruppia Maritima and Zostera marina to sulfide exposure around roots
Journal of Experimental Marine Biology and Ecology, 2015Co-Authors: M. Pedersen, Erik KristensenAbstract:Abstract Ruppia Maritima and Zostera marina often inhabit the same coastal areas and are often exposed to fairly high sulfide concentrations, with the former being most resilient. Our aim was to investigate differences in sulfide tolerance between the two species. Sensitivity towards sulfide in R. Maritima and Z. marina was investigated in split chambers that allowed exposure of roots to a range of sulfide concentrations, while the leaves were kept under optimal light and oxygen conditions. Roots of R. Maritima show a higher threshold towards sulfide (1.8–5.9 mM H 2 S) than those of Z. marina (0–0.5 mM H 2 S) after two weeks of incubation. The difference in sulfide sensitivity is attributed to different capacity of root oxygen leakage. Light and oxygen exposure enables oxygen transport from leaves down to the roots during both day and night. The oxic micro-shield around roots has a capacity to withstand sulfide intrusion until the sensitivity level is reached, when no other stressors are present. Leaves of exposed R. Maritima plants are affected at similar sulfide concentrations as roots, while leaves of Z. marina are affected at higher sulfide concentrations (1–3.5 mM H 2 S), reflecting different pathways of sulfide intrusion, root permeability and the ability to allocate energy away from exposed plant parts. Sensitivity towards sulfide occurs gradually and probably as a linear response to increasing sulfide concentration in R. Maritima , but the exact pattern in Z. marina is still unclear. Other external stressors, such as anoxia, shading, or increased temperature may change the thresholds of the species by affecting radial oxygen loss from roots, and make especially R. Maritima more prone to sulfide toxicity due to its highly permeable roots.
Kenneth A. Moore - One of the best experts on this subject based on the ideXlab platform.
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Impacts of Varying Estuarine Temperature and Light Conditions on Zostera marina (Eelgrass) and its Interactions With Ruppia Maritima (Widgeongrass)
Estuaries and Coasts, 2014Co-Authors: Kenneth A. Moore, Erin C. Shields, David B. ParrishAbstract:Seagrass populations have been declining globally, with changes attributed to anthropogenic stresses and, more recently, negative effects of global climate change. We examined the distribution of Zostera marina (eelgrass) dominated beds in the York River, Chesapeake Bay, VA over an 8-year time period. Using a temperature-dependent light model, declines in upriver areas were associated with higher light attenuation, resulting in lower light availability relative to compensating light requirements of Z . marina compared with downriver areas. An inverse relationship was observed between SAV growth and temperature with a change between net bed cover increases and decreases for the period of 2004–2011 observed at approximately 23 °C. Z . marina -dominated beds in the lower river have been recovering from a die-off event in 2005 and experienced another near complete decline in 2010, losing an average of 97 % of coverage of Z . marina from June to October. These 2010 declines were attributed to an early summer heat event in which daily mean water temperatures increased from 25 to 30 °C over a 2-week time period, considerably higher than previous years when complete die-offs were not observed. Z . marina recovery from this event was minimal, while Ruppia Maritima (widgeongrass) expanded its abundance. Water temperatures are projected to continue to increase in the Chesapeake Bay and elsewhere. These results suggest that short-term exposures to rapidly increasing temperatures by 4–5 °C above normal during summer months can result in widespread diebacks that may lead to Z . marina extirpation from historically vegetated areas, with the potential replacement by other species.
S.j. Klaine - One of the best experts on this subject based on the ideXlab platform.
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Effect of sulfate level on selenium uptake by Ruppia Maritima
Chemosphere, 1995Co-Authors: F.c. Bailey, A. W. Knight, R.s. Ogle, S.j. KlaineAbstract:Abstract Ruppia Maritima (wigeongrass), the dominant aquatic macrophyte in the agricultural drainage evaporation ponds of the Central Valley of California, is a food source for various waterfowl and shorebirds. Whole-plant uptake and accumulation of selenate (SeO4−2 or Se+6), selenite (SeO3−2 or Se+4), and seleno-methionine (Se−2) by R. Maritima from artificial evaporation pond water was compared over a 21 day period, and the effect of sulfate, a known selenate antagonist, on Se uptake was investigated. Plants were treated with 10, 100, or 1000 ug/l as selenium. Under both high and low sulfate conditions, R. Maritima was found to accumulate seleno-methionine to a much higher level than either selenite or selenate. However, under low sulfate conditions, selenate uptake was two orders of magnitude greater than under high sulfate conditions, indicating a sulfate/selenate antagonism. Bioconcentration factors for seleno-methionine under high and low sulfate conditions and for selenate under low sulfate conditions were very high (up to 21,800 for seleno-methionine and 1080 for selenate).
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Uptake of selenium by Ruppia Maritima from microcosm sediments under controlled redox conditions
1994Co-Authors: F.c. Bailey, J.l. Dunlap, S.j. KlaineAbstract:Redox potential plays a vital role in the speciation, bioavailability, and toxicity of metals and metalloids in sediments. The authors previously reported the development of a unique system which drives and maintains the redox of microcosm sediments with electrical current. The effectiveness of the redox control system has been validated by dosing microcosm sediments with acid volatile sulfide (AVS) and exerting either reducing conditions to maintain AVS or oxidizing conditions to induce a significant loss of AVS. Uptake of selenite, selenite and seleno-methionine from microcosm sediments by the aquatic plant Ruppia Maritima was determined under redox conditions appropriate for each selenium species. Selenate uptake was determined for oxidizing and neutral conditions, while selenite and seleno-methionine uptake was determined for neutral and reducing redox potentials.
Andy J. Green - One of the best experts on this subject based on the ideXlab platform.
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Waterbird impacts on widgeongrass Ruppia Maritima in a Mediterranean wetland: comparing bird groups and seasonal effects
Oikos, 2006Co-Authors: Hector Rodriguez-perez, Andy J. GreenAbstract:We studied the effect of waterbirds on the submerged macrophyte Ruppia Maritima in eleven fish ponds within Donana Natural Park (SW Spain). Separate exclosure designs allowed us to exclude flamingos or all waterbirds from 3 x 3 m plots within the ponds and compare them with control plots. Four experiments were conducted for three month periods at different points of the annual cycle with varying bird densities. Flamingos and wildfowl (ducks and coot) had significant negative additive effects on the presence of aboveground (leafs and shoots) or belowground (roots) parts of Ruppia at all times of the year. For plots where Ruppia was present, aboveground biomass was significantly higher in all-bird exclosures than in controls or flamingo exclosures. Presence and biomass of this annual plant varied significantly between seasons as did the density of seeds in sediments. Seasonal changes in seedbank densities were consistent with consumption by birds. There were no significant treatment ×season interactions for Ruppia presence, aboveground biomass or seeds. This is the first exclosure study to compare the effects of waterbirds on submerged macrophytes at different times throughout the annual cycle, and the first to compare simultaneously the effects of different bird groups. Our findings refute previous suggestions that major effects of waterbirds are limited to temperate regions and to periods of early growth or when major concentrations of migratory wildfowl are formed in autumn. Flamingos are important in structuring shallow wetlands in the Mediterranean, and possibly many other regions.
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Effects of seed ingestion and herbivory by waterfowl on seedling establishment: a field experiment with wigeongrass Ruppia Maritima in Doñana, south-west Spain
Plant Ecology, 2004Co-Authors: Jordi Figuerola, Andy J. GreenAbstract:The ingestion of seeds by vertebrates usually affects the viability and/or germination rate of seeds. Increases in germination rate following passage through the vertebrate gut have often been assumed to be favourable for seedling survival and plant fitness, but this assumption has never been tested experimentally. Given that numbers of herbivorous waterfowl are higher in winter in Mediterranean wetlands, herbivory pressure there will be higher for early growing plants. In a factorial experiment we investigated the effects of seed ingestion by ducks (shoveler, Anas clypeata ) on the survival of wigeongrass Ruppia Maritima seedlings in the field in Doñana (south-west Spain), under differing exposures to herbivory by waterfowl and fish. We planted ingested and non-ingested seeds in December, using exclosures to protect half of them from herbivores. When they were protected inside exclosures, there was no difference between ingested and non-ingested seeds in the number of plants that survived until June-July. However, fewer plants survived from ingested seeds when exposed to natural levels of herbivory because they were exposed for longer than plants germinating from non-ingested seeds. In conclusion, increases in germination rate after ingestion are not necessarily beneficial for the plant, and the final outcome depends on complex interactions with other factors such as herbivore abundance.
