Spatial Influences on Temporal Variations in Leaf Growth and Chemical Composition of Thalassia testudinum Banks Ex König in Tampa Bay, Florida

The importance of spatial influences on seasonal fluctuations in Thalassia testudinum leaf blade lengths and chemical constituents was demonstrated. Differences between samples from fringe and mid-bed for several constituents were significant and, if not accounted for, could affect the measurement of apparent seasonal cycles. Fringe-shoots, reflecting the influence of more intense grazing activity, had shorter leaf blade lengths, lower dry weights and carbohydrate levels, and higher protein levels than mid-bed shoots. Mid-bed rhizomes and roots had highest protein and ash levels reflecting possible sediment influence. Percent ash and protein in the rhizomes, and percent carbohydrate in the roots exhibited seasonal fluctuations, but the levels were different between fringe and mid-bed samples. Protein levels were greatest in shoots and roots, while carbohydrate levels were highest in rhizomes, illustrating the respective partitioning of biosynthetic and storage functions. The spatial differences seem to reflect gradients in biological and chemical interactions, and they may play an important role in trophic interactions in seagrass systems

Spatial Influences on Temporal Variations in Leaf Growth and Chemical Composition of Thalassia testudinum Banks Ex König in Tampa Bay, Florida

The importance of spatial influences on seasonal fluctuations in Thalassia testudinum leaf blade lengths and chemical constituents was demonstrated. Differences between samples from fringe and mid-bed for several constituents were significant and, if not accounted for, could affect the measurement of apparent seasonal cycles. Fringe-shoots, reflecting the influence of more intense grazing activity, had shorter leaf blade lengths, lower dry weights and carbohydrate levels, and higher protein levels than mid-bed shoots. Mid-bed rhizomes and roots had highest protein and ash levels reflecting possible sediment influence. Percent ash and protein in the rhizomes, and percent carbohydrate in the roots exhibited seasonal fluctuations, but the levels were different between fringe and mid-bed samples. Protein levels were greatest in shoots and roots, while carbohydrate levels were highest in rhizomes, illustrating the respective partitioning of biosynthetic and storage functions. The spatial differences seem to reflect gradients in biological and chemical interactions, and they may play an important role in trophic interactions in seagrass systems

A reassessment of Geminella (Chlorophyta) based upon photosynthetic pigments, DNA sequence analysis and electron microscopy

A cultured microalgal strain (UTEX 2540) originally identified as Heterotrichella gracillas Reisigl (Xanthophyceae) was re-examined using various techniques. Morphological evidence, particularly the absence of dimorphic cells (one blunt, the other tapered to an acute point), indicate that strain UTEX 2540 has been misidentified. Heterotrichella gracillas is considered to be a member of the chlorophyll a and c-containing class Xanthophyceae (Chromista). However, HPLC analyses of photosynthetic pigments indicated the presence of chlorophylls a and b, ß-carotene, lutein and violaxanthin while ultrastructural data revealed the presence of starch stored inside the plastid. These data, as well as small subunit (18S rRNA) gene sequence analysis, indicate that this alga belongs in the Chlorophyta, not the Xanthophyceae (Chromista). Further DNA sequence analyses suggest that UTEX 2540 is most closely related to Geminella terricola Petersen and certain Microspora species that are currently classified in the Ulotrichales. However, unlike other Geminella species, UTEX 2540 exists as single cells or forms poorly organized (2-8 celled) ephemeral pseudofilaments. A conspicuous extracellular mucilaginous sheath characterizes other Geminella species but this feature is lacking in UTEX 2540. Furthermore, our analyses convincingly demonstrate that Geminella and at least some isolates of Microspora do not belong in the Ulotrichales. These results suggest that (1) the generic concept for Geminella must be broadened to include unicellular species that lack an apparent mucilaginous envelope, (2) Geminella does not belong in the Ulotrichales, and, instead, (3) its closest relatives among other green algae are almost certainly found within the Trebouxiophyceae

Common ecological indicators identify changes in seagrass condition following disturbances in the Gulf of Mexico

Seagrasses are long-lived, clonal plants that can integrate fluctuations in environmental conditions over a range of temporal scales, from days to years, and can act as barometers of coastal change. There are many estimated seagrass traits and ecosystem parameters that have the potential to reflect ecosystem status, linking seagrass condition to natural and anthropogenic drivers of change. We identified five seagrass indicators and seven metrics that are suitable, affordable and frequently measured by 38 monitoring programs across the Gulf of Mexico (GoM). A specific set of ratings and assessment points were formulated for each measurable metric. We determined metric ratings (Acceptable, Concerning, Alarming) and validated assessment points using long-term monitoring data from Texas and Florida, coupled with existing literature and input from a panel of seagrass biologists. We reported scores using a blue-gray-orange (Acceptable-Concerning-Alarming) scale to summarize information in a format accessible to the public, resource managers, stakeholders, and policymakers. Seagrass percent cover, shoot allometry and species composition were sensitive indicators of large-scale climatic disturbances (droughts, hurricanes). Severe drought led to reductions in total seagrass cover and leaf length in Upper Laguna Madre, Texas, and Florida Bay; however, Syringodium filiforme was disproportionally affected in Texas while Thalassia testudinum beds responded strongly to drought impacts in Florida. Hurricanes Harvey (TX) and Irma (FL) also resulted in loss of seagrass cover and diminished leaf length in the Texas Coastal Bend and Florida Keys; both storms largely impacted T. testudinum and to a lesser extent, S. filiforme. Many of the metrics within these affected bays and basins received either a “Concerning” or “Alarming” rating, driven by the impacts of these disturbances. Our proposed indicators serve as a tool to evaluate seagrass condition at the bay or basin scale. Moreover, the indicators, metrics, and assessment points are amenable to large-scale evaluations of ecosystem condition because they are economically feasible. This framework may provide the foundation for a comprehensive assessment of seagrass status and trends across the entire GoM

Predicting Carbon Isotope Discrimination in Eelgrass (Zostera marina L.) From the Environmental Parameters- Light, Flow, and [DIC]

Isotopic discrimination against 13C during photosynthesis is determined by a combination of environmental conditions and physiological mechanisms that control delivery of CO2 to RUBISCO. This study investigated the effects of light, flow, dissolved inorganic carbon (DIC) concentration, and its speciation, on photosynthetic carbon assimilation of Zostera marinaL. (eelgrass) using a combination of laboratory experiments and theoretical calculations leading to a mechanistic understanding of environmental conditions that influence leaf carbon uptake and determine leaf stable carbon isotope signatures δ13C. Photosynthesis was saturated with respect to flow at low velocity ~ 3 cm s-1, but was strongly influenced by [DIC], and particularly aqueous CO2 (CO2(aq)) under all flow conditions. The non-linear responses of light- and flow-saturated photosynthesis to [DIC] were used to quantify the maximum physiological capacity for photosynthesis, and to determine the degree of photosynthetic carbon limitation for light-saturated photosynthesis, which provided a mechanistic pathway for modeling regulation of carbon uptake and 13C discrimination. Model predictions of δ13C spanned the typical range of values reported for a variety of seagrass taxa, and were most sensitive to [DIC] (predominantly [CO2(aq) ]) and flow, but less sensitive to DIC source [CO2(aq)vs. HCO¯3]. These results provide a predictive understanding of the role of key environmental parameters (light, flow, and DIC availability) can have in driving δ13C of seagrasses, which will become increasingly important for predicting the response of these ecosystem engineers to local processes that affect light availability and flow, as well as global impacts of climate warming and ocean acidification in the Anthropocene

Gender Difference in 2-Year Mortality and Immunological Response to ART in an HIV-Infected Chinese Population, 2006–2008

Since it was initiated in 2002, the China Free Antiretroviral Treatment (ART) Program has been progressing from an emergency response to a standardized treatment and care system. As of December 31, 2009, a total of 81,880 patients in 31 provinces, autonomous regions, and special municipalities received free ART. Gender differences, however, in mortality and immunological response to ART in this cohort have never been described.To understand whether women and men who enrolled in the China National Free ART Program responded equally well to the treatment.A retrospective analysis of the national free ART databases from June 2006-December 2008 was performed. HIV-infected subjects who were 18 years or older, ART naïve at baseline, and on a 3TC regimen enrolled in the program from June 1 to December 31, 2006, were included in this study, then followed up to 2 years.Among 3457 enrolled subjects who met the inclusion criteria, 59.2% were male and 40.8% female. The majority of the subjects were 19-44 years old (77%) and married (72%). Over the full 24 months of follow-up, the mortality rate was 19.0% in males and 11.4% in females (p = 0.0014). Males on therapy for 3-24 months were more likely to die than females (HR = 1.46, 95% CI: 1.04-2.06, p = 0.0307) after adjusting for baseline characteristics. Compared to men, women had higher CD4+ counts over time after initiating ART (p<0.0001).Our study showed that women had an overall lower mortality and higher CD4+ counts than men in response to ART treatment, which may be attributed to adherence, biological factors, social, cultural and economic reasons. Further study is needed to explore these factors that might contribute to the gender differences in mortality and immunological response to ART

Seagrass Canopy Photosynthetic Response Is a Function of Canopy Density and Light Environment: A Model for Amphibolis griffithii

A three-dimensional computer model of canopies of the seagrass Amphibolis griffithii was used to investigate the consequences of variations in canopy structure and benthic light environment on leaf-level photosynthetic saturation state. The model was constructed using empirical data of plant morphometrics from a previously conducted shading experiment and validated well to in-situ data on light attenuation in canopies of different densities. Using published values of the leaf-level saturating irradiance for photosynthesis, results show that the interaction of canopy density and canopy-scale photosynthetic response is complex and non-linear, due to the combination of self-shading and the non-linearity of photosynthesis versus irradiance (P-I) curves near saturating irradiance. Therefore studies of light limitation in seagrasses should consider variation in canopy structure and density. Based on empirical work, we propose a number of possible measures for canopy scale photosynthetic response that can be plotted to yield isoclines in the space of canopy density and light environment. These plots can be used to interpret the significance of canopy changes induced as a response to decreases in the benthic light environment: in some cases canopy thinning can lead to an equivalent leaf level light environment, in others physiological changes may also be required but these alone may be inadequate for canopy survival. By providing insight to these processes the methods developed here could be a valuable management tool for seagrass conservation during dredging or other coastal developments