1,486 research outputs found
Recommended from our members
Effects of dredge deposits on seagrasses : an integrative model for Laguna Madre : concluding report. Volume I, Executive Summary.
No full textInteragency Coordination Team, U.S. Army Corps of Engineers, Galveston District, The University of Texas Marine Science Institute, Texas A&M University Department of Oceanography, Texas Parks and Wildlife DepartmentThis report presents the results of an interdisciplinary collaborative effort to develop an integrative model for
seagrass productivity in Laguna Madre. One of the major components of this integrative model is the Laguna
Madre Seagrass Model (LMSM) which was designed to interface with other component models described in this
report, including carbon and nitrogen allocation, sediment diagenesis, and spectral irradiance and radiative
transfer. Linkage with hydrodynamic and sediment transport models provided a potentially valuable
management tool to assess the effects of maintenance dredging and resuspension of dredged material deposits
on seagrasses of Laguna Madre.Texas A&M University and the U.S. Army Corps of Engineers (Galveston District) 96-PL-03Marine Scienc
Recommended from our members
Effects of dredge deposits on seagrasses : an integrative model for Laguna Madre : concluding report. Volume II, Findings.
No full textInteragency Coordination Team, U.S. Army Corps of Engineers, Galveston District, The University of Texas Marine Science Institute, Texas A&M University Department of Oceanography, Texas Parks and Wildlife DepartmentThis report presents the results of an interdisciplinary collaborative effort to develop an integrative model for
seagrass productivity in Laguna Madre. One of the major components of this integrative model is the Laguna
Madre Seagrass Model (LMSM) which was designed to interface with other component models described in this
report, including carbon and nitrogen allocation, sediment diagenesis, and spectral irradiance and radiative
transfer. Linkage with hydrodynamic and sediment transport models provided a potentially valuable
management tool to assess the effects of maintenance dredging and resuspension of dredged material deposits
on seagrasses of Laguna Madre.Texas A&M University and the U.S. Army Corps of Engineers (Galveston District) 96-PL-03Marine Scienc
Recommended from our members
Growth and photosynthetic responses of two subtropical seagrasses, Thalassia testudinum and Halodule wrightii to in situ manipulations of irradiance
No full textThe growth and photosynthetic responses of two species of subtropical seagrasses, Thalassia testudinum and Halodule wrightii, were examined in relation to reductions in underwater light. Shade screens reduced irradiance to roughly 30% and 20% of in situ ambient (ISA). Short shoots of T. testudinum had a greater ability to tolerate a ten month period of light reduction as demonstrated by the longer survival of plants exposed to 30% ISA. Evidence for photoadaptation was observed in plants from shaded treatments compared to unshaded controls (plants receiving 100% ISA). Leaf elongation rates were lower in T. testudinum plants exposed to 20% ISA for one month (October 1992 to November 1992) compared to plants receiving 100% ISA, but there were no differences between treatments for the months of January, February, March, and May. However, by July both levels of shaded T. testudinum had significantly lower growth rates compared to plants receiving 100% ISA. Water temperatures above 25°C and the depletion of stored reserves by spring growth most likely contributed to the disappearance of all short shoots of T. testudinum shaded at 20% ISA and both shaded plots of H. wrightii by August 1993. Photosynthesis versus irradiance (P vs. I) parameters revealed significant differences in the rates of light saturated photosynthesis (P [subscript max]), respiration, saturation irradiance (I [subscript k]), and relative quantum efficiency (α) between the two species. In particular, the significantly lower respiration rates of Thalassia testudinum (89.8 ± 8.4 μmol O₂ gdw⁻¹ h⁻¹ at 30°C) compared to Halodule wrightii (186.0 ± 20.0 μmol O₂ gdw⁻¹ h⁻¹ at 30°C ) may contribute to its survival in light-limited environments. Respiration rates and P [subscript max] for both species significantly increased with seasonal increases in temperature. No significant differences were noted in shaded versus unshaded H. wrightii at 20°C or 30°C; however, in T. testudinum, after four months of shading at 20% ISA, P [subscript max] was significantly lower and α significantly higher relative to unshaded controls. The lower growth rates and increased light harvesting capability of T. testudinum in response to reduced irradiance reflects the K-selected strategy of this species compared to H. wrightiiMarine Scienc
Recommended from our members
Inorganic nitrogen uptake by two kelp species, Laminaria solidungula and Laminaria saccharina, in the Alaskan High Arctic
No full textThe uptake of inorganic nitrate (NO₃⁻) and ammonium (NH₄⁺) by two co-occurring species of kelp, Laminaria solidungula and Laminaria saccharina, was compared using entire plants incubated under natural conditions in the field and in the laboratory. Field experiments were conducted in situ during ice-covered and open-water periods in the Boulder Patch kelp bed community in the Alaskan Beaufort Sea. The data obtained in these experiments do not provide evidence of Michaelis-Menten saturation kinetics. The uptake of NO₃⁻ and NH₄⁺ by both species appears to be a linear function of substrate concentration with no evidence of a saturating concentration although average substrate concentrations approach 80 μM. There was no significant difference between NO₃⁻ and NH₄⁺ uptake rates in conditions where either NO₃⁻ or NH₄⁺ were supplied at the same concentrations and no significant difference in uptake rates between species. The mean uptake rate at ambient nitrate concentrations in winter (4 - 7 μM) was 0.53 /μmoles gdw⁻¹h⁻¹. Uptake rate values obtained by substrate disappearance at ambient concentrations were corroborated by measurements of ¹⁵N stable isotope incorporation. Dark and light-exposed plants of both species also exhibited equivalent rates of uptake in short-term experiments with either NO₃⁻ or NH₄⁺ present as substrate. L. solidungula also demonstrated equal dark/light uptake with both nitrogen substrates present, revealing no competitive inhibition of either substrate. Time course disappearance for L. solidungula with NO₃⁻ or NH₄⁺ and NO₃⁻/NH₄⁺ followed second order kinetics. Water motion was shown to significantly enhance both NO₃⁻ and NH₄⁺ disappearance for L. solidungula. Linear growth rates in juvenile L. solidungula sporophytes were not affected by NO₃⁻ concentration, but this may be related to the translocation of organic nitrogen to support linear growth at low NO₃⁻ concentrations, based on the bleaching of distal blade tissues in nitrogen-starved plants. The nitrogen uptake rates determined in this study for both species at -1.8 to 5 °C agree closely with published uptake rates for temperate kelp species living at 15 °C, enabling L. solidungula and L. saccharina to maintain high growth rates at the low temperatures characteristic of polar environmentsMarine Scienc
Recommended from our members
Impacts of human disturbances on seagrass communities in the Padre Island National Seashore
No full textHuman trampling effects, such as those from wade fishermen, on seagrasses and surrounding sediments were examined using experimental trampling lanes in the Padre Island National Seashore (PAIS) in South Texas. Six sites were established throughout three regions in PAIS (Bird Island, Yarborough Pass, and Nine-Mile Hole). At each site control, low intensity, and high intensity treatments were randomly assigned to one of three 2.5-m by 5-m trampling lanes. The plots were trampled monthly from April to June 2003 and then repeated at six different sites from September to December 2003. Water column, sediment, and seagrass characteristics were measured prior to initial trampling, and two, four, and 10 months after trampling initiation. Sites trampled in spring were also sampled 16 months after initial sampling event to assess long-term seagrass recovery. After four months of spring and fall trampling, reductions in Halodule wrightii percent cover were evident in all low and high intensity lanes except for one low intensity lane during the fall trampling. By the end of the spring and fall experiments, two low intensity and six high intensity lanes remained lower than the control lanes. Resistance (condition immediately after trampling), tolerance (condition 6-12 months after trampling) and resilience (recovery over a defined period after trampling) indices were calculated to compare trampling responses in the three regions. Seagrasses in Bird Island, where higher shoot densities were consistently measured, were the most resistant to trampling in the spring (59.0%) and fall (77.5%) experiments. Yarborough Pass seagrass beds were more resilient to trampling by the end of the spring (76.3%, month 16) and fall (98.8%, month 10). The lower resilience index in the spring combined with extremely high root:shoot ratios (10.0 to 79.2) at the start of the spring experiment suggest a seasonal response to trampling. However, no long-term effects were detected as the low and high intensity lanes in this region all returned to 100% H. wrightii cover by the end of the experiment. Seagrass response in Nine-Mile Hole was extremely variable and a complete seagrass die-off in all lanes (control, low intensity, high intensity) at one site in that region occurred during the spring experiment. This die-off could possibly be a result of ammonium toxicity. Excessive porewater ammonium concentrations were measured at this site throughout the entire experiment (352 to 1000 μM) and appear to contribute to the instability of this region. Despite the general trends detected in each region, variability in the data makes it difficult to conclude with certainty whether H. wrightii was or was not affected by trampling in PAIS. Natural variability inherent to the system can be more important in determining seagrass distribution than localized disturbancesMarine Scienc
Recommended from our members
Patterns in iscoscapes and N:P stoichioscapes of the dominant seagrasses (Halodule wrightii and Thalassia testudinum) in the western Gulf of Mexico
No full textSeagrasses assimilate carbon (C), nitrogen (N), and phosphorus (P) from the water column and sediment, making their tissue nutrient content an excellent bioindicator of long-term, system-wide environmental conditions. I examined the role of seagrasses as ecological indicators of water quality and nutrient loading in three Texas estuarine systems through examination of their tissue isotopic (δ¹³C and δ¹⁵N) and stoichiometric (N:P) ratios over a period of five years using maps of spatial patterns in isotopic and stoichiometric regimes (“isoscapes” and stoichioscapes”). Leaf tissue samples were collected from the dominant Texas seagrasses, Halodule wrightii and Thalassia testudinum, at 567 stations during annual sampling between 2011 and 2015. Tissues were analyzed for C, N, and P content and C and N isotopic composition. Data were used to develop interpolated maps of variations in seagrass δ¹³C and δ¹⁵N signatures and N:P ratios in the Mission-Aransas NERR, Corpus Christi Bay, and upper and lower Laguna Madre. Regions where seagrasses had significantly enriched δ¹⁵N signatures, depleted δ¹³C signatures, or elevated N:P ratios were often associated with areas of urbanization or development. This was supported by significant relationships between δ¹⁵N and δ¹³C clusters and distance from outlets draining high population watersheds. I also documented a distinct temporal shift in δ¹³C signatures and N:P ratios across the study areas. The change in δ¹³C signatures was particularly notable in H. wrightii in 2015, when δ¹³C signatures became more depleted and N:P ratios were elevated, following an influx of freshwater and nutrients ending a three-year drought in south Texas. The spatial and temporal variation in seagrass tissue C content reported here reflects inputs of freshwater and riverine DIC as well as changes in the benthic light environment, while the N and P dynamics reported suggest that N:P ratios and δ¹⁵N signatures of seagrasses on the Texas coast are accurate bioindicators of nutrient loading in these estuaries. These metrics may thus serve as early indicators of changes in water quality.Marine Scienc
Recommended from our members
Understanding factors that control seagrass reproductive success in sub-tropical ecosystems
No full texttextSeagrasses are submerged marine plants that provide essential ecosystem functions, but are declining in abundance worldwide. As angiosperms, seagrasses are capable of sexual reproduction, but also propagate asexually through clonal rhizome growth. Clonal growth was traditionally considered the primary means for seagrass propagation. Recent developments in genetic techniques and an increasing number of studies examining seagrass population genetics, however, indicate that sexual reproduction is important for bed establishment and maintenance. Few studies have investigated the reproductive biology and ecology of sub-tropical seagrass species, although this information is necessary for effective management and restoration. This work investigates the influence of pore-water nutrients on flowering, water flow on seed dispersal, consumption on seed survival, and describes the reproductive phenology in Texas for the two dominant seagrass species in the Gulf of Mexico: turtle grass (Thalassia testudinum) and shoal grass (Halodule wrightii). These species exhibit distinctive reproductive seasons that span summertime months, but reproductive output varies spatially and temporally. Results of an in situ nutrient enrichment experiment indicate that turtle grass produces fewer flowers (but more somatic tissue) when exposed to high pore-water ammonium than when exposed to low pore-water ammonium, suggesting that nutrient loading has the potential to reduce seagrass reproductive output. Seed consumption may also limit reproduction and recruitment in some areas, as laboratory feeding experiments show that several local crustaceans consume shoal grass and turtle grass seeds and seedlings, which do not survive consumption. Dispersal experiments indicate that seed movement along the substrate depends on local water flow conditions, is greater for turtle grass than shoal grass, and is related to seed morphology. Under normal water flow conditions in Texas, turtle grass secondary seedling dispersal is relatively minimal (< 2.1 m d⁻¹) compared to primary dispersal, which can be on the order of kilometers, and shoal grass secondary seed dispersal can be up to 1.1 m d⁻¹, but seeds are likely retained in the parent meadow. Results from this work can be used when developing seagrass management, conservation and restoration actions and provide necessary information concerning a life history stage whose importance was historically under-recognized.Marine Scienc
Recommended from our members
Trophodynamics of the benthic food webs in the Chukchi and Beaufort Seas, Alaska
No full texttextThe Chukchi and Beaufort Sea shelves host diverse and productive seafloor ecosystems important for carbon and nitrogen cycling for the Arctic Ocean. The benthic food web transfers energy from primary producers to high trophic level organisms (e.g., birds, fish, and mammals), which are important for cultural practices and subsistence hunting by Native Alaskans. This work focuses on the trophic ecology of arctic food webs through use of several different approaches. First, variation in the natural abundance of stable carbon and nitrogen isotopes facilitated the identification of trophic pathways and, subsequently, allowed the comparison of trophic guilds and food webs from the Chukchi and Beaufort Seas. Compared to water column and sedimentary organic matter end-members, second trophic level grazers and suspension feeders were conspicuously ¹³C-enriched throughout the Chukchi Sea, which supports the hypothesis that microbial degradation of organic matter occurred prior to metazoan assimilation. Second, food web recovery from disturbances caused by exploratory oil drilling at the seafloor that had occurred approximately 20 years prior were assessed in both the Chukchi and Beaufort Seas. Based on isotopic trophic niche overlap between organisms common to drilled and reference sites in the Chukchi and Beaufort Seas, the oil drilling sites had similar food web structure, indicating recovery from the activity associated with the drilling process. Third, photosynthetic pigment biomarkers were used to better understand the diagenetic process, specifically focusing on how both microbial and metazoan grazing pathways degrade organic matter in relation to seasonal sea ice retreat in the Chukchi Sea. The benthic macrofaunal and microbial food web caused rapid degradation of organic matter upon the initial pulse of microalgal food sources to the seafloor. These diagenetic pathways are linked to the ¹³C-enrichment of residual organic matter, which corresponds to the stable isotope values measured in the benthic macrofauna. Lastly, high-precision liquid chromatography and spectrophotometry were compared for estimating sedimentary pigments in the marine environment. Substantial differences in pheopigment (chlorophyll degradation products) concentrations were observed between the two techniques, suggesting the need for revisions to the monochromatic spectrophotometric equation that relates absorbance to pigment concentrations. One pheopigment, pheophorbide, was found to interfere with the accuracy of the spectrophotometric equation and caused the overestimation of pheopigments.Marine Scienc
Recommended from our members
An assessment of seagrass and tidal flat recovery from anthropogenic physical disturbance events along the Padre Island National Seashore
No full texttextPropeller scars and off-road vehicle (ORV) tracks are readily visible in aerial photographs and their areal extent can be easily measured using the latest techniques in GIS technology. The objectives of my study were to establish a baseline of seagrass and wind-tidal flat scarring along the Padre Island National Seashore for future monitoring, to determine the persistence of wind-tidal flat ORV tracks from historical aerial photographs, and to examine the recovery of seagrass propeller scars by comparing 2002 and 2005 aerial photographs. Over the area examined, the total number of propeller scars decreased 29%, and the total number of ORV tracks increased 28% between 2002 and 2005. Propeller scars appeared to take less than three years to recover. Historical photograph analysis showed that ORV tracks have persisted in the wind-tidal flats since the 1960's and show no sign of recovery. This work represents the first attempt to measure seagrass and tidal flat scarring intensity and recovery time from physical disturbances in the Padre Island National Seashore.Marine Scienc
Recommended from our members
Abundance, production and carbon dynamics of the seagrass, Thalassia testudinum in Corpus Christi Bay, Texas
No full textThe seasonal production dynamics of the subtropical seagrass, Thalassia testudinum, were examined through measurements of biomass, leaf growth and carbohydrate carbon content from plants collected in Corpus Christi Bay from December 1993 to March 1995. Daily photon flux densities (PFD) showed strong seasonal variations, ranging from 9.6 mol m⁻² d⁻¹ in April to 21.7 mol m⁻² d⁻¹ in July. Shoot density and biomass changed significantly with season; values ranged from 321 shoots m⁻² (454 g dry wt m⁻²) in March to 531 shoots m⁻² (885 g dry wt m⁻²) in September. Rhizome tissues tended to have the highest biomass while root tissue had the lowest. Leaf productivities showed significant seasonal variation that were strongly correlated with temperature, ranging from 0.07 g dry wt m⁻² d⁻¹ in December to 5.6 g dry wt m⁻² d⁻¹ in July. Chlorophyll (chl) concentrations were significantly higher and chl a:b ratios lowest during the spring/summer period of maximum photosynthetic production and growth than during winter. Soluble carbohydrate carbon content was highest in rhizome tissues (111-203 mg C g⁻¹ dry wt) and lowest in leaf tissues (46-70 mg C g⁻¹ dry wt), which is consistent with the rhizome's role as a carbon storage tissue. Soluble rhizome carbohydrate carbon content increased rapidly during June and July, which coincided with high water temperatures, underwater irradiance and blade chlorophyll concentrations. During winter and early spring, rhizome carbohydrate carbon content dropped nearly 50%, suggesting that these reserves were mobilized for maintenance and growth. Estimated annual biomass production of Thalassia testudinum in Corpus Christi Bay over the period of this study was 1320 g dry wt m⁻² yr⁻¹, equivalent to 422 g C m⁻² yr⁻¹. To assess the effects of light reduction on Thalassia testudinum, shade screens were used to reduce underwater light to 1628 mol m⁻² yr⁻¹ (14% of surface irradiance, SI) and 864 mol m⁻² yr⁻¹ (5% SI) starting in April 1993. All plants subjected to 5% SI died after 200 days and over 99% of plants receiving 14% SI died by the end of the experiment (490 days). Blade widths of plants in the controls ranged from 6.4 to 7.0 mm, and decreased to 4.7 mm as a result of light reduction. Leaf production rates were significantly higher in control plants compared to plants within the 14% and 5% SI treatments, with all plants showing a seasonal trend with high productivity in July and low productivity in April. Blade chlorophyll concentrations increased, while the chl a:b ratio decreased with reduced light level. In both light treatments rhizome soluble carbohydrate carbon content was 50% lower and leaf carbohydrate carbon content was about 15% lower than controls, while the root carbohydrate content did not differ significantly between treatments and controls (no decrease in structural carbohydrate carbon content was noted between treatments). Pore water ammonium and sulfide concentrations in the shaded cages were significantly higher than in control cages. Thalassia testudinum in Corpus Christi Bay exhibited a strong seasonal growth cycle in which changes in rhizome carbohydrate reserves and chlorophyll content may be under endogenous control as triggered by a combination of temperature and/or light period. In contrast to the seagrass Halodule, Thalassia maintained a larger carbohydrate reserve and exhibited a stronger physiological response to light reduction, which may contribute to its competitive superiorityMarine Scienc
- …
